linux - fs/buffer.c

3563 lines · 92.5 KiB

1	/*
2	* linux/fs/buffer.c
3	*
4	* Copyright (C) 1991, 1992, 2002 Linus Torvalds
5	*/
6
7	/*
8	* Start bdflush() with kernel_thread not syscall - Paul Gortmaker, 12/95
9	*
10	* Removed a lot of unnecessary code and simplified things now that
11	* the buffer cache isn't our primary cache - Andrew Tridgell 12/96
12	*
13	* Speed up hash, lru, and free list operations. Use gfp() for allocating
14	* hash table, use SLAB cache for buffer heads. SMP threading. -DaveM
15	*
16	* Added 32k buffer block sizes - these are required older ARM systems. - RMK
17	*
18	* async buffer flushing, 1999 Andrea Arcangeli <[email protected]>
19	*/
20
21	#include <linux/kernel.h>
22	#include <linux/sched/signal.h>
23	#include <linux/syscalls.h>
24	#include <linux/fs.h>
25	#include <linux/iomap.h>
26	#include <linux/mm.h>
27	#include <linux/percpu.h>
28	#include <linux/slab.h>
29	#include <linux/capability.h>
30	#include <linux/blkdev.h>
31	#include <linux/file.h>
32	#include <linux/quotaops.h>
33	#include <linux/highmem.h>
34	#include <linux/export.h>
35	#include <linux/backing-dev.h>
36	#include <linux/writeback.h>
37	#include <linux/hash.h>
38	#include <linux/suspend.h>
39	#include <linux/buffer_head.h>
40	#include <linux/task_io_accounting_ops.h>
41	#include <linux/bio.h>
42	#include <linux/notifier.h>
43	#include <linux/cpu.h>
44	#include <linux/bitops.h>
45	#include <linux/mpage.h>
46	#include <linux/bit_spinlock.h>
47	#include <linux/pagevec.h>
48	#include <trace/events/block.h>
49
50	static int fsync_buffers_list(spinlock_t lock, struct list_head list);
51	static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
52	enum rw_hint hint, struct writeback_control *wbc);
53
54	#define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
55
56	inline void touch_buffer(struct buffer_head *bh)
57	{
58	trace_block_touch_buffer(bh);
59	mark_page_accessed(bh->b_page);
60	}
61	EXPORT_SYMBOL(touch_buffer);
62
63	void __lock_buffer(struct buffer_head *bh)
64	{
65	wait_on_bit_lock_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
66	}
67	EXPORT_SYMBOL(__lock_buffer);
68
69	void unlock_buffer(struct buffer_head *bh)
70	{
71	clear_bit_unlock(BH_Lock, &bh->b_state);
72	smp_mb__after_atomic();
73	wake_up_bit(&bh->b_state, BH_Lock);
74	}
75	EXPORT_SYMBOL(unlock_buffer);
76
77	/*
78	* Returns if the page has dirty or writeback buffers. If all the buffers
79	* are unlocked and clean then the PageDirty information is stale. If
80	* any of the pages are locked, it is assumed they are locked for IO.
81	*/
82	void buffer_check_dirty_writeback(struct page *page,
83	bool dirty, bool writeback)
84	{
85	struct buffer_head head, bh;
86	*dirty = false;
87	*writeback = false;
88
89	BUG_ON(!PageLocked(page));
90
91	if (!page_has_buffers(page))
92	return;
93
94	if (PageWriteback(page))
95	*writeback = true;
96
97	head = page_buffers(page);
98	bh = head;
99	do {
100	if (buffer_locked(bh))
101	*writeback = true;
102
103	if (buffer_dirty(bh))
104	*dirty = true;
105
106	bh = bh->b_this_page;
107	} while (bh != head);
108	}
109	EXPORT_SYMBOL(buffer_check_dirty_writeback);
110
111	/*
112	* Block until a buffer comes unlocked. This doesn't stop it
113	* from becoming locked again - you have to lock it yourself
114	* if you want to preserve its state.
115	*/
116	void __wait_on_buffer(struct buffer_head * bh)
117	{
118	wait_on_bit_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
119	}
120	EXPORT_SYMBOL(__wait_on_buffer);
121
122	static void
123	__clear_page_buffers(struct page *page)
124	{
125	ClearPagePrivate(page);
126	set_page_private(page, 0);
127	put_page(page);
128	}
129
130	static void buffer_io_error(struct buffer_head bh, char msg)
131	{
132	if (!test_bit(BH_Quiet, &bh->b_state))
133	printk_ratelimited(KERN_ERR
134	"Buffer I/O error on dev %pg, logical block %llu%s\n",
135	bh->b_bdev, (unsigned long long)bh->b_blocknr, msg);
136	}
137
138	/*
139	* End-of-IO handler helper function which does not touch the bh after
140	* unlocking it.
141	* Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
142	* a race there is benign: unlock_buffer() only use the bh's address for
143	* hashing after unlocking the buffer, so it doesn't actually touch the bh
144	* itself.
145	*/
146	static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
147	{
148	if (uptodate) {
149	set_buffer_uptodate(bh);
150	} else {
151	/* This happens, due to failed read-ahead attempts. */
152	clear_buffer_uptodate(bh);
153	}
154	unlock_buffer(bh);
155	}
156
157	/*
158	* Default synchronous end-of-IO handler.. Just mark it up-to-date and
159	* unlock the buffer. This is what ll_rw_block uses too.
160	*/
161	void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
162	{
163	__end_buffer_read_notouch(bh, uptodate);
164	put_bh(bh);
165	}
166	EXPORT_SYMBOL(end_buffer_read_sync);
167
168	void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
169	{
170	if (uptodate) {
171	set_buffer_uptodate(bh);
172	} else {
173	buffer_io_error(bh, ", lost sync page write");
174	mark_buffer_write_io_error(bh);
175	clear_buffer_uptodate(bh);
176	}
177	unlock_buffer(bh);
178	put_bh(bh);
179	}
180	EXPORT_SYMBOL(end_buffer_write_sync);
181
182	/*
183	* Various filesystems appear to want __find_get_block to be non-blocking.
184	* But it's the page lock which protects the buffers. To get around this,
185	* we get exclusion from try_to_free_buffers with the blockdev mapping's
186	* private_lock.
187	*
188	* Hack idea: for the blockdev mapping, private_lock contention
189	* may be quite high. This code could TryLock the page, and if that
190	* succeeds, there is no need to take private_lock.
191	*/
192	static struct buffer_head *
193	__find_get_block_slow(struct block_device *bdev, sector_t block)
194	{
195	struct inode *bd_inode = bdev->bd_inode;
196	struct address_space *bd_mapping = bd_inode->i_mapping;
197	struct buffer_head *ret = NULL;
198	pgoff_t index;
199	struct buffer_head *bh;
200	struct buffer_head *head;
201	struct page *page;
202	int all_mapped = 1;
203
204	index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
205	page = find_get_page_flags(bd_mapping, index, FGP_ACCESSED);
206	if (!page)
207	goto out;
208
209	spin_lock(&bd_mapping->private_lock);
210	if (!page_has_buffers(page))
211	goto out_unlock;
212	head = page_buffers(page);
213	bh = head;
214	do {
215	if (!buffer_mapped(bh))
216	all_mapped = 0;
217	else if (bh->b_blocknr == block) {
218	ret = bh;
219	get_bh(bh);
220	goto out_unlock;
221	}
222	bh = bh->b_this_page;
223	} while (bh != head);
224
225	/* we might be here because some of the buffers on this page are
226	* not mapped. This is due to various races between
227	* file io on the block device and getblk. It gets dealt with
228	* elsewhere, don't buffer_error if we had some unmapped buffers
229	*/
230	if (all_mapped) {
231	printk("__find_get_block_slow() failed. "
232	"block=%llu, b_blocknr=%llu\n",
233	(unsigned long long)block,
234	(unsigned long long)bh->b_blocknr);
235	printk("b_state=0x%08lx, b_size=%zu\n",
236	bh->b_state, bh->b_size);
237	printk("device %pg blocksize: %d\n", bdev,
238	1 << bd_inode->i_blkbits);
239	}
240	out_unlock:
241	spin_unlock(&bd_mapping->private_lock);
242	put_page(page);
243	out:
244	return ret;
245	}
246
247	/*
248	* I/O completion handler for block_read_full_page() - pages
249	* which come unlocked at the end of I/O.
250	*/
251	static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
252	{
253	unsigned long flags;
254	struct buffer_head *first;
255	struct buffer_head *tmp;
256	struct page *page;
257	int page_uptodate = 1;
258
259	BUG_ON(!buffer_async_read(bh));
260
261	page = bh->b_page;
262	if (uptodate) {
263	set_buffer_uptodate(bh);
264	} else {
265	clear_buffer_uptodate(bh);
266	buffer_io_error(bh, ", async page read");
267	SetPageError(page);
268	}
269
270	/*
271	* Be _very_ careful from here on. Bad things can happen if
272	* two buffer heads end IO at almost the same time and both
273	* decide that the page is now completely done.
274	*/
275	first = page_buffers(page);
276	local_irq_save(flags);
277	bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
278	clear_buffer_async_read(bh);
279	unlock_buffer(bh);
280	tmp = bh;
281	do {
282	if (!buffer_uptodate(tmp))
283	page_uptodate = 0;
284	if (buffer_async_read(tmp)) {
285	BUG_ON(!buffer_locked(tmp));
286	goto still_busy;
287	}
288	tmp = tmp->b_this_page;
289	} while (tmp != bh);
290	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
291	local_irq_restore(flags);
292
293	/*
294	* If none of the buffers had errors and they are all
295	* uptodate then we can set the page uptodate.
296	*/
297	if (page_uptodate && !PageError(page))
298	SetPageUptodate(page);
299	unlock_page(page);
300	return;
301
302	still_busy:
303	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
304	local_irq_restore(flags);
305	return;
306	}
307
308	/*
309	* Completion handler for block_write_full_page() - pages which are unlocked
310	* during I/O, and which have PageWriteback cleared upon I/O completion.
311	*/
312	void end_buffer_async_write(struct buffer_head *bh, int uptodate)
313	{
314	unsigned long flags;
315	struct buffer_head *first;
316	struct buffer_head *tmp;
317	struct page *page;
318
319	BUG_ON(!buffer_async_write(bh));
320
321	page = bh->b_page;
322	if (uptodate) {
323	set_buffer_uptodate(bh);
324	} else {
325	buffer_io_error(bh, ", lost async page write");
326	mark_buffer_write_io_error(bh);
327	clear_buffer_uptodate(bh);
328	SetPageError(page);
329	}
330
331	first = page_buffers(page);
332	local_irq_save(flags);
333	bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
334
335	clear_buffer_async_write(bh);
336	unlock_buffer(bh);
337	tmp = bh->b_this_page;
338	while (tmp != bh) {
339	if (buffer_async_write(tmp)) {
340	BUG_ON(!buffer_locked(tmp));
341	goto still_busy;
342	}
343	tmp = tmp->b_this_page;
344	}
345	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
346	local_irq_restore(flags);
347	end_page_writeback(page);
348	return;
349
350	still_busy:
351	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
352	local_irq_restore(flags);
353	return;
354	}
355	EXPORT_SYMBOL(end_buffer_async_write);
356
357	/*
358	* If a page's buffers are under async readin (end_buffer_async_read
359	* completion) then there is a possibility that another thread of
360	* control could lock one of the buffers after it has completed
361	* but while some of the other buffers have not completed. This
362	* locked buffer would confuse end_buffer_async_read() into not unlocking
363	* the page. So the absence of BH_Async_Read tells end_buffer_async_read()
364	* that this buffer is not under async I/O.
365	*
366	* The page comes unlocked when it has no locked buffer_async buffers
367	* left.
368	*
369	* PageLocked prevents anyone starting new async I/O reads any of
370	* the buffers.
371	*
372	* PageWriteback is used to prevent simultaneous writeout of the same
373	* page.
374	*
375	* PageLocked prevents anyone from starting writeback of a page which is
376	* under read I/O (PageWriteback is only ever set against a locked page).
377	*/
378	static void mark_buffer_async_read(struct buffer_head *bh)
379	{
380	bh->b_end_io = end_buffer_async_read;
381	set_buffer_async_read(bh);
382	}
383
384	static void mark_buffer_async_write_endio(struct buffer_head *bh,
385	bh_end_io_t *handler)
386	{
387	bh->b_end_io = handler;
388	set_buffer_async_write(bh);
389	}
390
391	void mark_buffer_async_write(struct buffer_head *bh)
392	{
393	mark_buffer_async_write_endio(bh, end_buffer_async_write);
394	}
395	EXPORT_SYMBOL(mark_buffer_async_write);
396
397
398	/*
399	* fs/buffer.c contains helper functions for buffer-backed address space's
400	* fsync functions. A common requirement for buffer-based filesystems is
401	* that certain data from the backing blockdev needs to be written out for
402	* a successful fsync(). For example, ext2 indirect blocks need to be
403	* written back and waited upon before fsync() returns.
404	*
405	* The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
406	* inode_has_buffers() and invalidate_inode_buffers() are provided for the
407	* management of a list of dependent buffers at ->i_mapping->private_list.
408	*
409	* Locking is a little subtle: try_to_free_buffers() will remove buffers
410	* from their controlling inode's queue when they are being freed. But
411	* try_to_free_buffers() will be operating against the blockdev mapping
412	* at the time, not against the S_ISREG file which depends on those buffers.
413	* So the locking for private_list is via the private_lock in the address_space
414	* which backs the buffers. Which is different from the address_space
415	* against which the buffers are listed. So for a particular address_space,
416	* mapping->private_lock does not protect mapping->private_list! In fact,
417	* mapping->private_list will always be protected by the backing blockdev's
418	* ->private_lock.
419	*
420	* Which introduces a requirement: all buffers on an address_space's
421	* ->private_list must be from the same address_space: the blockdev's.
422	*
423	* address_spaces which do not place buffers at ->private_list via these
424	* utility functions are free to use private_lock and private_list for
425	* whatever they want. The only requirement is that list_empty(private_list)
426	* be true at clear_inode() time.
427	*
428	* FIXME: clear_inode should not call invalidate_inode_buffers(). The
429	* filesystems should do that. invalidate_inode_buffers() should just go
430	* BUG_ON(!list_empty).
431	*
432	* FIXME: mark_buffer_dirty_inode() is a data-plane operation. It should
433	* take an address_space, not an inode. And it should be called
434	* mark_buffer_dirty_fsync() to clearly define why those buffers are being
435	* queued up.
436	*
437	* FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
438	* list if it is already on a list. Because if the buffer is on a list,
439	* it must already be on the right one. If not, the filesystem is being
440	* silly. This will save a ton of locking. But first we have to ensure
441	* that buffers are taken off the old inode's list when they are freed
442	* (presumably in truncate). That requires careful auditing of all
443	* filesystems (do it inside bforget()). It could also be done by bringing
444	* b_inode back.
445	*/
446
447	/*
448	* The buffer's backing address_space's private_lock must be held
449	*/
450	static void __remove_assoc_queue(struct buffer_head *bh)
451	{
452	list_del_init(&bh->b_assoc_buffers);
453	WARN_ON(!bh->b_assoc_map);
454	bh->b_assoc_map = NULL;
455	}
456
457	int inode_has_buffers(struct inode *inode)
458	{
459	return !list_empty(&inode->i_data.private_list);
460	}
461
462	/*
463	* osync is designed to support O_SYNC io. It waits synchronously for
464	* all already-submitted IO to complete, but does not queue any new
465	* writes to the disk.
466	*
467	* To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
468	* you dirty the buffers, and then use osync_inode_buffers to wait for
469	* completion. Any other dirty buffers which are not yet queued for
470	* write will not be flushed to disk by the osync.
471	*/
472	static int osync_buffers_list(spinlock_t lock, struct list_head list)
473	{
474	struct buffer_head *bh;
475	struct list_head *p;
476	int err = 0;
477
478	spin_lock(lock);
479	repeat:
480	list_for_each_prev(p, list) {
481	bh = BH_ENTRY(p);
482	if (buffer_locked(bh)) {
483	get_bh(bh);
484	spin_unlock(lock);
485	wait_on_buffer(bh);
486	if (!buffer_uptodate(bh))
487	err = -EIO;
488	brelse(bh);
489	spin_lock(lock);
490	goto repeat;
491	}
492	}
493	spin_unlock(lock);
494	return err;
495	}
496
497	void emergency_thaw_bdev(struct super_block *sb)
498	{
499	while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
500	printk(KERN_WARNING "Emergency Thaw on %pg\n", sb->s_bdev);
501	}
502
503	/**
504	* sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
505	* @mapping: the mapping which wants those buffers written
506	*
507	* Starts I/O against the buffers at mapping->private_list, and waits upon
508	* that I/O.
509	*
510	* Basically, this is a convenience function for fsync().
511	* @mapping is a file or directory which needs those buffers to be written for
512	* a successful fsync().
513	*/
514	int sync_mapping_buffers(struct address_space *mapping)
515	{
516	struct address_space *buffer_mapping = mapping->private_data;
517
518	if (buffer_mapping == NULL \|\| list_empty(&mapping->private_list))
519	return 0;
520
521	return fsync_buffers_list(&buffer_mapping->private_lock,
522	&mapping->private_list);
523	}
524	EXPORT_SYMBOL(sync_mapping_buffers);
525
526	/*
527	* Called when we've recently written block `bblock', and it is known that
528	* `bblock' was for a buffer_boundary() buffer. This means that the block at
529	* `bblock + 1' is probably a dirty indirect block. Hunt it down and, if it's
530	* dirty, schedule it for IO. So that indirects merge nicely with their data.
531	*/
532	void write_boundary_block(struct block_device *bdev,
533	sector_t bblock, unsigned blocksize)
534	{
535	struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
536	if (bh) {
537	if (buffer_dirty(bh))
538	ll_rw_block(REQ_OP_WRITE, 0, 1, &bh);
539	put_bh(bh);
540	}
541	}
542
543	void mark_buffer_dirty_inode(struct buffer_head bh, struct inode inode)
544	{
545	struct address_space *mapping = inode->i_mapping;
546	struct address_space *buffer_mapping = bh->b_page->mapping;
547
548	mark_buffer_dirty(bh);
549	if (!mapping->private_data) {
550	mapping->private_data = buffer_mapping;
551	} else {
552	BUG_ON(mapping->private_data != buffer_mapping);
553	}
554	if (!bh->b_assoc_map) {
555	spin_lock(&buffer_mapping->private_lock);
556	list_move_tail(&bh->b_assoc_buffers,
557	&mapping->private_list);
558	bh->b_assoc_map = mapping;
559	spin_unlock(&buffer_mapping->private_lock);
560	}
561	}
562	EXPORT_SYMBOL(mark_buffer_dirty_inode);
563
564	/*
565	* Mark the page dirty, and set it dirty in the radix tree, and mark the inode
566	* dirty.
567	*
568	* If warn is true, then emit a warning if the page is not uptodate and has
569	* not been truncated.
570	*
571	* The caller must hold lock_page_memcg().
572	*/
573	void __set_page_dirty(struct page page, struct address_space mapping,
574	int warn)
575	{
576	unsigned long flags;
577
578	xa_lock_irqsave(&mapping->i_pages, flags);
579	if (page->mapping) { /* Race with truncate? */
580	WARN_ON_ONCE(warn && !PageUptodate(page));
581	account_page_dirtied(page, mapping);
582	radix_tree_tag_set(&mapping->i_pages,
583	page_index(page), PAGECACHE_TAG_DIRTY);
584	}
585	xa_unlock_irqrestore(&mapping->i_pages, flags);
586	}
587	EXPORT_SYMBOL_GPL(__set_page_dirty);
588
589	/*
590	* Add a page to the dirty page list.
591	*
592	* It is a sad fact of life that this function is called from several places
593	* deeply under spinlocking. It may not sleep.
594	*
595	* If the page has buffers, the uptodate buffers are set dirty, to preserve
596	* dirty-state coherency between the page and the buffers. It the page does
597	* not have buffers then when they are later attached they will all be set
598	* dirty.
599	*
600	* The buffers are dirtied before the page is dirtied. There's a small race
601	* window in which a writepage caller may see the page cleanness but not the
602	* buffer dirtiness. That's fine. If this code were to set the page dirty
603	* before the buffers, a concurrent writepage caller could clear the page dirty
604	* bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
605	* page on the dirty page list.
606	*
607	* We use private_lock to lock against try_to_free_buffers while using the
608	* page's buffer list. Also use this to protect against clean buffers being
609	* added to the page after it was set dirty.
610	*
611	* FIXME: may need to call ->reservepage here as well. That's rather up to the
612	* address_space though.
613	*/
614	int __set_page_dirty_buffers(struct page *page)
615	{
616	int newly_dirty;
617	struct address_space *mapping = page_mapping(page);
618
619	if (unlikely(!mapping))
620	return !TestSetPageDirty(page);
621
622	spin_lock(&mapping->private_lock);
623	if (page_has_buffers(page)) {
624	struct buffer_head *head = page_buffers(page);
625	struct buffer_head *bh = head;
626
627	do {
628	set_buffer_dirty(bh);
629	bh = bh->b_this_page;
630	} while (bh != head);
631	}
632	/*
633	* Lock out page->mem_cgroup migration to keep PageDirty
634	* synchronized with per-memcg dirty page counters.
635	*/
636	lock_page_memcg(page);
637	newly_dirty = !TestSetPageDirty(page);
638	spin_unlock(&mapping->private_lock);
639
640	if (newly_dirty)
641	__set_page_dirty(page, mapping, 1);
642
643	unlock_page_memcg(page);
644
645	if (newly_dirty)
646	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
647
648	return newly_dirty;
649	}
650	EXPORT_SYMBOL(__set_page_dirty_buffers);
651
652	/*
653	* Write out and wait upon a list of buffers.
654	*
655	* We have conflicting pressures: we want to make sure that all
656	* initially dirty buffers get waited on, but that any subsequently
657	* dirtied buffers don't. After all, we don't want fsync to last
658	* forever if somebody is actively writing to the file.
659	*
660	* Do this in two main stages: first we copy dirty buffers to a
661	* temporary inode list, queueing the writes as we go. Then we clean
662	* up, waiting for those writes to complete.
663	*
664	* During this second stage, any subsequent updates to the file may end
665	* up refiling the buffer on the original inode's dirty list again, so
666	* there is a chance we will end up with a buffer queued for write but
667	* not yet completed on that list. So, as a final cleanup we go through
668	* the osync code to catch these locked, dirty buffers without requeuing
669	* any newly dirty buffers for write.
670	*/
671	static int fsync_buffers_list(spinlock_t lock, struct list_head list)
672	{
673	struct buffer_head *bh;
674	struct list_head tmp;
675	struct address_space *mapping;
676	int err = 0, err2;
677	struct blk_plug plug;
678
679	INIT_LIST_HEAD(&tmp);
680	blk_start_plug(&plug);
681
682	spin_lock(lock);
683	while (!list_empty(list)) {
684	bh = BH_ENTRY(list->next);
685	mapping = bh->b_assoc_map;
686	__remove_assoc_queue(bh);
687	/* Avoid race with mark_buffer_dirty_inode() which does
688	* a lockless check and we rely on seeing the dirty bit */
689	smp_mb();
690	if (buffer_dirty(bh) \|\| buffer_locked(bh)) {
691	list_add(&bh->b_assoc_buffers, &tmp);
692	bh->b_assoc_map = mapping;
693	if (buffer_dirty(bh)) {
694	get_bh(bh);
695	spin_unlock(lock);
696	/*
697	* Ensure any pending I/O completes so that
698	* write_dirty_buffer() actually writes the
699	* current contents - it is a noop if I/O is
700	* still in flight on potentially older
701	* contents.
702	*/
703	write_dirty_buffer(bh, REQ_SYNC);
704
705	/*
706	* Kick off IO for the previous mapping. Note
707	* that we will not run the very last mapping,
708	* wait_on_buffer() will do that for us
709	* through sync_buffer().
710	*/
711	brelse(bh);
712	spin_lock(lock);
713	}
714	}
715	}
716
717	spin_unlock(lock);
718	blk_finish_plug(&plug);
719	spin_lock(lock);
720
721	while (!list_empty(&tmp)) {
722	bh = BH_ENTRY(tmp.prev);
723	get_bh(bh);
724	mapping = bh->b_assoc_map;
725	__remove_assoc_queue(bh);
726	/* Avoid race with mark_buffer_dirty_inode() which does
727	* a lockless check and we rely on seeing the dirty bit */
728	smp_mb();
729	if (buffer_dirty(bh)) {
730	list_add(&bh->b_assoc_buffers,
731	&mapping->private_list);
732	bh->b_assoc_map = mapping;
733	}
734	spin_unlock(lock);
735	wait_on_buffer(bh);
736	if (!buffer_uptodate(bh))
737	err = -EIO;
738	brelse(bh);
739	spin_lock(lock);
740	}
741
742	spin_unlock(lock);
743	err2 = osync_buffers_list(lock, list);
744	if (err)
745	return err;
746	else
747	return err2;
748	}
749
750	/*
751	* Invalidate any and all dirty buffers on a given inode. We are
752	* probably unmounting the fs, but that doesn't mean we have already
753	* done a sync(). Just drop the buffers from the inode list.
754	*
755	* NOTE: we take the inode's blockdev's mapping's private_lock. Which
756	* assumes that all the buffers are against the blockdev. Not true
757	* for reiserfs.
758	*/
759	void invalidate_inode_buffers(struct inode *inode)
760	{
761	if (inode_has_buffers(inode)) {
762	struct address_space *mapping = &inode->i_data;
763	struct list_head *list = &mapping->private_list;
764	struct address_space *buffer_mapping = mapping->private_data;
765
766	spin_lock(&buffer_mapping->private_lock);
767	while (!list_empty(list))
768	__remove_assoc_queue(BH_ENTRY(list->next));
769	spin_unlock(&buffer_mapping->private_lock);
770	}
771	}
772	EXPORT_SYMBOL(invalidate_inode_buffers);
773
774	/*
775	* Remove any clean buffers from the inode's buffer list. This is called
776	* when we're trying to free the inode itself. Those buffers can pin it.
777	*
778	* Returns true if all buffers were removed.
779	*/
780	int remove_inode_buffers(struct inode *inode)
781	{
782	int ret = 1;
783
784	if (inode_has_buffers(inode)) {
785	struct address_space *mapping = &inode->i_data;
786	struct list_head *list = &mapping->private_list;
787	struct address_space *buffer_mapping = mapping->private_data;
788
789	spin_lock(&buffer_mapping->private_lock);
790	while (!list_empty(list)) {
791	struct buffer_head *bh = BH_ENTRY(list->next);
792	if (buffer_dirty(bh)) {
793	ret = 0;
794	break;
795	}
796	__remove_assoc_queue(bh);
797	}
798	spin_unlock(&buffer_mapping->private_lock);
799	}
800	return ret;
801	}
802
803	/*
804	* Create the appropriate buffers when given a page for data area and
805	* the size of each buffer.. Use the bh->b_this_page linked list to
806	* follow the buffers created. Return NULL if unable to create more
807	* buffers.
808	*
809	* The retry flag is used to differentiate async IO (paging, swapping)
810	* which may not fail from ordinary buffer allocations.
811	*/
812	struct buffer_head alloc_page_buffers(struct page page, unsigned long size,
813	bool retry)
814	{
815	struct buffer_head bh, head;
816	gfp_t gfp = GFP_NOFS;
817	long offset;
818
819	if (retry)
820	gfp \|= __GFP_NOFAIL;
821
822	head = NULL;
823	offset = PAGE_SIZE;
824	while ((offset -= size) >= 0) {
825	bh = alloc_buffer_head(gfp);
826	if (!bh)
827	goto no_grow;
828
829	bh->b_this_page = head;
830	bh->b_blocknr = -1;
831	head = bh;
832
833	bh->b_size = size;
834
835	/* Link the buffer to its page */
836	set_bh_page(bh, page, offset);
837	}
838	return head;
839	/*
840	* In case anything failed, we just free everything we got.
841	*/
842	no_grow:
843	if (head) {
844	do {
845	bh = head;
846	head = head->b_this_page;
847	free_buffer_head(bh);
848	} while (head);
849	}
850
851	return NULL;
852	}
853	EXPORT_SYMBOL_GPL(alloc_page_buffers);
854
855	static inline void
856	link_dev_buffers(struct page page, struct buffer_head head)
857	{
858	struct buffer_head bh, tail;
859
860	bh = head;
861	do {
862	tail = bh;
863	bh = bh->b_this_page;
864	} while (bh);
865	tail->b_this_page = head;
866	attach_page_buffers(page, head);
867	}
868
869	static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
870	{
871	sector_t retval = ~((sector_t)0);
872	loff_t sz = i_size_read(bdev->bd_inode);
873
874	if (sz) {
875	unsigned int sizebits = blksize_bits(size);
876	retval = (sz >> sizebits);
877	}
878	return retval;
879	}
880
881	/*
882	* Initialise the state of a blockdev page's buffers.
883	*/
884	static sector_t
885	init_page_buffers(struct page page, struct block_device bdev,
886	sector_t block, int size)
887	{
888	struct buffer_head *head = page_buffers(page);
889	struct buffer_head *bh = head;
890	int uptodate = PageUptodate(page);
891	sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode), size);
892
893	do {
894	if (!buffer_mapped(bh)) {
895	bh->b_end_io = NULL;
896	bh->b_private = NULL;
897	bh->b_bdev = bdev;
898	bh->b_blocknr = block;
899	if (uptodate)
900	set_buffer_uptodate(bh);
901	if (block < end_block)
902	set_buffer_mapped(bh);
903	}
904	block++;
905	bh = bh->b_this_page;
906	} while (bh != head);
907
908	/*
909	* Caller needs to validate requested block against end of device.
910	*/
911	return end_block;
912	}
913
914	/*
915	* Create the page-cache page that contains the requested block.
916	*
917	* This is used purely for blockdev mappings.
918	*/
919	static int
920	grow_dev_page(struct block_device *bdev, sector_t block,
921	pgoff_t index, int size, int sizebits, gfp_t gfp)
922	{
923	struct inode *inode = bdev->bd_inode;
924	struct page *page;
925	struct buffer_head *bh;
926	sector_t end_block;
927	int ret = 0; /* Will call free_more_memory() */
928	gfp_t gfp_mask;
929
930	gfp_mask = mapping_gfp_constraint(inode->i_mapping, ~__GFP_FS) \| gfp;
931
932	/*
933	* XXX: __getblk_slow() can not really deal with failure and
934	* will endlessly loop on improvised global reclaim. Prefer
935	* looping in the allocator rather than here, at least that
936	* code knows what it's doing.
937	*/
938	gfp_mask \|= __GFP_NOFAIL;
939
940	page = find_or_create_page(inode->i_mapping, index, gfp_mask);
941
942	BUG_ON(!PageLocked(page));
943
944	if (page_has_buffers(page)) {
945	bh = page_buffers(page);
946	if (bh->b_size == size) {
947	end_block = init_page_buffers(page, bdev,
948	(sector_t)index << sizebits,
949	size);
950	goto done;
951	}
952	if (!try_to_free_buffers(page))
953	goto failed;
954	}
955
956	/*
957	* Allocate some buffers for this page
958	*/
959	bh = alloc_page_buffers(page, size, true);
960
961	/*
962	* Link the page to the buffers and initialise them. Take the
963	* lock to be atomic wrt __find_get_block(), which does not
964	* run under the page lock.
965	*/
966	spin_lock(&inode->i_mapping->private_lock);
967	link_dev_buffers(page, bh);
968	end_block = init_page_buffers(page, bdev, (sector_t)index << sizebits,
969	size);
970	spin_unlock(&inode->i_mapping->private_lock);
971	done:
972	ret = (block < end_block) ? 1 : -ENXIO;
973	failed:
974	unlock_page(page);
975	put_page(page);
976	return ret;
977	}
978
979	/*
980	* Create buffers for the specified block device block's page. If
981	* that page was dirty, the buffers are set dirty also.
982	*/
983	static int
984	grow_buffers(struct block_device *bdev, sector_t block, int size, gfp_t gfp)
985	{
986	pgoff_t index;
987	int sizebits;
988
989	sizebits = -1;
990	do {
991	sizebits++;
992	} while ((size << sizebits) < PAGE_SIZE);
993
994	index = block >> sizebits;
995
996	/*
997	* Check for a block which wants to lie outside our maximum possible
998	* pagecache index. (this comparison is done using sector_t types).
999	*/
1000	if (unlikely(index != block >> sizebits)) {
1001	printk(KERN_ERR "%s: requested out-of-range block %llu for "
1002	"device %pg\n",
1003	__func__, (unsigned long long)block,
1004	bdev);
1005	return -EIO;
1006	}
1007
1008	/* Create a page with the proper size buffers.. */
1009	return grow_dev_page(bdev, block, index, size, sizebits, gfp);
1010	}
1011
1012	static struct buffer_head *
1013	__getblk_slow(struct block_device *bdev, sector_t block,
1014	unsigned size, gfp_t gfp)
1015	{
1016	/* Size must be multiple of hard sectorsize */
1017	if (unlikely(size & (bdev_logical_block_size(bdev)-1) \|\|
1018	(size < 512 \|\| size > PAGE_SIZE))) {
1019	printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1020	size);
1021	printk(KERN_ERR "logical block size: %d\n",
1022	bdev_logical_block_size(bdev));
1023
1024	dump_stack();
1025	return NULL;
1026	}
1027
1028	for (;;) {
1029	struct buffer_head *bh;
1030	int ret;
1031
1032	bh = __find_get_block(bdev, block, size);
1033	if (bh)
1034	return bh;
1035
1036	ret = grow_buffers(bdev, block, size, gfp);
1037	if (ret < 0)
1038	return NULL;
1039	}
1040	}
1041
1042	/*
1043	* The relationship between dirty buffers and dirty pages:
1044	*
1045	* Whenever a page has any dirty buffers, the page's dirty bit is set, and
1046	* the page is tagged dirty in its radix tree.
1047	*
1048	* At all times, the dirtiness of the buffers represents the dirtiness of
1049	* subsections of the page. If the page has buffers, the page dirty bit is
1050	* merely a hint about the true dirty state.
1051	*
1052	* When a page is set dirty in its entirety, all its buffers are marked dirty
1053	* (if the page has buffers).
1054	*
1055	* When a buffer is marked dirty, its page is dirtied, but the page's other
1056	* buffers are not.
1057	*
1058	* Also. When blockdev buffers are explicitly read with bread(), they
1059	* individually become uptodate. But their backing page remains not
1060	* uptodate - even if all of its buffers are uptodate. A subsequent
1061	* block_read_full_page() against that page will discover all the uptodate
1062	* buffers, will set the page uptodate and will perform no I/O.
1063	*/
1064
1065	/**
1066	* mark_buffer_dirty - mark a buffer_head as needing writeout
1067	* @bh: the buffer_head to mark dirty
1068	*
1069	* mark_buffer_dirty() will set the dirty bit against the buffer, then set its
1070	* backing page dirty, then tag the page as dirty in its address_space's radix
1071	* tree and then attach the address_space's inode to its superblock's dirty
1072	* inode list.
1073	*
1074	* mark_buffer_dirty() is atomic. It takes bh->b_page->mapping->private_lock,
1075	* i_pages lock and mapping->host->i_lock.
1076	*/
1077	void mark_buffer_dirty(struct buffer_head *bh)
1078	{
1079	WARN_ON_ONCE(!buffer_uptodate(bh));
1080
1081	trace_block_dirty_buffer(bh);
1082
1083	/*
1084	* Very carefully optimize the it-is-already-dirty case.
1085	*
1086	* Don't let the final "is it dirty" escape to before we
1087	* perhaps modified the buffer.
1088	*/
1089	if (buffer_dirty(bh)) {
1090	smp_mb();
1091	if (buffer_dirty(bh))
1092	return;
1093	}
1094
1095	if (!test_set_buffer_dirty(bh)) {
1096	struct page *page = bh->b_page;
1097	struct address_space *mapping = NULL;
1098
1099	lock_page_memcg(page);
1100	if (!TestSetPageDirty(page)) {
1101	mapping = page_mapping(page);
1102	if (mapping)
1103	__set_page_dirty(page, mapping, 0);
1104	}
1105	unlock_page_memcg(page);
1106	if (mapping)
1107	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1108	}
1109	}
1110	EXPORT_SYMBOL(mark_buffer_dirty);
1111
1112	void mark_buffer_write_io_error(struct buffer_head *bh)
1113	{
1114	set_buffer_write_io_error(bh);
1115	/* FIXME: do we need to set this in both places? */
1116	if (bh->b_page && bh->b_page->mapping)
1117	mapping_set_error(bh->b_page->mapping, -EIO);
1118	if (bh->b_assoc_map)
1119	mapping_set_error(bh->b_assoc_map, -EIO);
1120	}
1121	EXPORT_SYMBOL(mark_buffer_write_io_error);
1122
1123	/*
1124	* Decrement a buffer_head's reference count. If all buffers against a page
1125	* have zero reference count, are clean and unlocked, and if the page is clean
1126	* and unlocked then try_to_free_buffers() may strip the buffers from the page
1127	* in preparation for freeing it (sometimes, rarely, buffers are removed from
1128	* a page but it ends up not being freed, and buffers may later be reattached).
1129	*/
1130	void __brelse(struct buffer_head * buf)
1131	{
1132	if (atomic_read(&buf->b_count)) {
1133	put_bh(buf);
1134	return;
1135	}
1136	WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1137	}
1138	EXPORT_SYMBOL(__brelse);
1139
1140	/*
1141	* bforget() is like brelse(), except it discards any
1142	* potentially dirty data.
1143	*/
1144	void __bforget(struct buffer_head *bh)
1145	{
1146	clear_buffer_dirty(bh);
1147	if (bh->b_assoc_map) {
1148	struct address_space *buffer_mapping = bh->b_page->mapping;
1149
1150	spin_lock(&buffer_mapping->private_lock);
1151	list_del_init(&bh->b_assoc_buffers);
1152	bh->b_assoc_map = NULL;
1153	spin_unlock(&buffer_mapping->private_lock);
1154	}
1155	__brelse(bh);
1156	}
1157	EXPORT_SYMBOL(__bforget);
1158
1159	static struct buffer_head __bread_slow(struct buffer_head bh)
1160	{
1161	lock_buffer(bh);
1162	if (buffer_uptodate(bh)) {
1163	unlock_buffer(bh);
1164	return bh;
1165	} else {
1166	get_bh(bh);
1167	bh->b_end_io = end_buffer_read_sync;
1168	submit_bh(REQ_OP_READ, 0, bh);
1169	wait_on_buffer(bh);
1170	if (buffer_uptodate(bh))
1171	return bh;
1172	}
1173	brelse(bh);
1174	return NULL;
1175	}
1176
1177	/*
1178	* Per-cpu buffer LRU implementation. To reduce the cost of __find_get_block().
1179	* The bhs[] array is sorted - newest buffer is at bhs[0]. Buffers have their
1180	* refcount elevated by one when they're in an LRU. A buffer can only appear
1181	* once in a particular CPU's LRU. A single buffer can be present in multiple
1182	* CPU's LRUs at the same time.
1183	*
1184	* This is a transparent caching front-end to sb_bread(), sb_getblk() and
1185	* sb_find_get_block().
1186	*
1187	* The LRUs themselves only need locking against invalidate_bh_lrus. We use
1188	* a local interrupt disable for that.
1189	*/
1190
1191	#define BH_LRU_SIZE 16
1192
1193	struct bh_lru {
1194	struct buffer_head *bhs[BH_LRU_SIZE];
1195	};
1196
1197	static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1198
1199	#ifdef CONFIG_SMP
1200	#define bh_lru_lock() local_irq_disable()
1201	#define bh_lru_unlock() local_irq_enable()
1202	#else
1203	#define bh_lru_lock() preempt_disable()
1204	#define bh_lru_unlock() preempt_enable()
1205	#endif
1206
1207	static inline void check_irqs_on(void)
1208	{
1209	#ifdef irqs_disabled
1210	BUG_ON(irqs_disabled());
1211	#endif
1212	}
1213
1214	/*
1215	* Install a buffer_head into this cpu's LRU. If not already in the LRU, it is
1216	* inserted at the front, and the buffer_head at the back if any is evicted.
1217	* Or, if already in the LRU it is moved to the front.
1218	*/
1219	static void bh_lru_install(struct buffer_head *bh)
1220	{
1221	struct buffer_head *evictee = bh;
1222	struct bh_lru *b;
1223	int i;
1224
1225	check_irqs_on();
1226	bh_lru_lock();
1227
1228	b = this_cpu_ptr(&bh_lrus);
1229	for (i = 0; i < BH_LRU_SIZE; i++) {
1230	swap(evictee, b->bhs[i]);
1231	if (evictee == bh) {
1232	bh_lru_unlock();
1233	return;
1234	}
1235	}
1236
1237	get_bh(bh);
1238	bh_lru_unlock();
1239	brelse(evictee);
1240	}
1241
1242	/*
1243	* Look up the bh in this cpu's LRU. If it's there, move it to the head.
1244	*/
1245	static struct buffer_head *
1246	lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1247	{
1248	struct buffer_head *ret = NULL;
1249	unsigned int i;
1250
1251	check_irqs_on();
1252	bh_lru_lock();
1253	for (i = 0; i < BH_LRU_SIZE; i++) {
1254	struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
1255
1256	if (bh && bh->b_blocknr == block && bh->b_bdev == bdev &&
1257	bh->b_size == size) {
1258	if (i) {
1259	while (i) {
1260	__this_cpu_write(bh_lrus.bhs[i],
1261	__this_cpu_read(bh_lrus.bhs[i - 1]));
1262	i--;
1263	}
1264	__this_cpu_write(bh_lrus.bhs[0], bh);
1265	}
1266	get_bh(bh);
1267	ret = bh;
1268	break;
1269	}
1270	}
1271	bh_lru_unlock();
1272	return ret;
1273	}
1274
1275	/*
1276	* Perform a pagecache lookup for the matching buffer. If it's there, refresh
1277	* it in the LRU and mark it as accessed. If it is not present then return
1278	* NULL
1279	*/
1280	struct buffer_head *
1281	__find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1282	{
1283	struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1284
1285	if (bh == NULL) {
1286	/* __find_get_block_slow will mark the page accessed */
1287	bh = __find_get_block_slow(bdev, block);
1288	if (bh)
1289	bh_lru_install(bh);
1290	} else
1291	touch_buffer(bh);
1292
1293	return bh;
1294	}
1295	EXPORT_SYMBOL(__find_get_block);
1296
1297	/*
1298	* __getblk_gfp() will locate (and, if necessary, create) the buffer_head
1299	* which corresponds to the passed block_device, block and size. The
1300	* returned buffer has its reference count incremented.
1301	*
1302	* __getblk_gfp() will lock up the machine if grow_dev_page's
1303	* try_to_free_buffers() attempt is failing. FIXME, perhaps?
1304	*/
1305	struct buffer_head *
1306	__getblk_gfp(struct block_device *bdev, sector_t block,
1307	unsigned size, gfp_t gfp)
1308	{
1309	struct buffer_head *bh = __find_get_block(bdev, block, size);
1310
1311	might_sleep();
1312	if (bh == NULL)
1313	bh = __getblk_slow(bdev, block, size, gfp);
1314	return bh;
1315	}
1316	EXPORT_SYMBOL(__getblk_gfp);
1317
1318	/*
1319	* Do async read-ahead on a buffer..
1320	*/
1321	void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1322	{
1323	struct buffer_head *bh = __getblk(bdev, block, size);
1324	if (likely(bh)) {
1325	ll_rw_block(REQ_OP_READ, REQ_RAHEAD, 1, &bh);
1326	brelse(bh);
1327	}
1328	}
1329	EXPORT_SYMBOL(__breadahead);
1330
1331	/**
1332	* __bread_gfp() - reads a specified block and returns the bh
1333	* @bdev: the block_device to read from
1334	* @block: number of block
1335	* @size: size (in bytes) to read
1336	* @gfp: page allocation flag
1337	*
1338	* Reads a specified block, and returns buffer head that contains it.
1339	* The page cache can be allocated from non-movable area
1340	* not to prevent page migration if you set gfp to zero.
1341	* It returns NULL if the block was unreadable.
1342	*/
1343	struct buffer_head *
1344	__bread_gfp(struct block_device *bdev, sector_t block,
1345	unsigned size, gfp_t gfp)
1346	{
1347	struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
1348
1349	if (likely(bh) && !buffer_uptodate(bh))
1350	bh = __bread_slow(bh);
1351	return bh;
1352	}
1353	EXPORT_SYMBOL(__bread_gfp);
1354
1355	/*
1356	* invalidate_bh_lrus() is called rarely - but not only at unmount.
1357	* This doesn't race because it runs in each cpu either in irq
1358	* or with preempt disabled.
1359	*/
1360	static void invalidate_bh_lru(void *arg)
1361	{
1362	struct bh_lru *b = &get_cpu_var(bh_lrus);
1363	int i;
1364
1365	for (i = 0; i < BH_LRU_SIZE; i++) {
1366	brelse(b->bhs[i]);
1367	b->bhs[i] = NULL;
1368	}
1369	put_cpu_var(bh_lrus);
1370	}
1371
1372	static bool has_bh_in_lru(int cpu, void *dummy)
1373	{
1374	struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
1375	int i;
1376
1377	for (i = 0; i < BH_LRU_SIZE; i++) {
1378	if (b->bhs[i])
1379	return 1;
1380	}
1381
1382	return 0;
1383	}
1384
1385	void invalidate_bh_lrus(void)
1386	{
1387	on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1, GFP_KERNEL);
1388	}
1389	EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1390
1391	void set_bh_page(struct buffer_head *bh,
1392	struct page *page, unsigned long offset)
1393	{
1394	bh->b_page = page;
1395	BUG_ON(offset >= PAGE_SIZE);
1396	if (PageHighMem(page))
1397	/*
1398	* This catches illegal uses and preserves the offset:
1399	*/
1400	bh->b_data = (char *)(0 + offset);
1401	else
1402	bh->b_data = page_address(page) + offset;
1403	}
1404	EXPORT_SYMBOL(set_bh_page);
1405
1406	/*
1407	* Called when truncating a buffer on a page completely.
1408	*/
1409
1410	/* Bits that are cleared during an invalidate */
1411	#define BUFFER_FLAGS_DISCARD \
1412	(1 << BH_Mapped \| 1 << BH_New \| 1 << BH_Req \| \
1413	1 << BH_Delay \| 1 << BH_Unwritten)
1414
1415	static void discard_buffer(struct buffer_head * bh)
1416	{
1417	unsigned long b_state, b_state_old;
1418
1419	lock_buffer(bh);
1420	clear_buffer_dirty(bh);
1421	bh->b_bdev = NULL;
1422	b_state = bh->b_state;
1423	for (;;) {
1424	b_state_old = cmpxchg(&bh->b_state, b_state,
1425	(b_state & ~BUFFER_FLAGS_DISCARD));
1426	if (b_state_old == b_state)
1427	break;
1428	b_state = b_state_old;
1429	}
1430	unlock_buffer(bh);
1431	}
1432
1433	/**
1434	* block_invalidatepage - invalidate part or all of a buffer-backed page
1435	*
1436	* @page: the page which is affected
1437	* @offset: start of the range to invalidate
1438	* @length: length of the range to invalidate
1439	*
1440	* block_invalidatepage() is called when all or part of the page has become
1441	* invalidated by a truncate operation.
1442	*
1443	* block_invalidatepage() does not have to release all buffers, but it must
1444	* ensure that no dirty buffer is left outside @offset and that no I/O
1445	* is underway against any of the blocks which are outside the truncation
1446	* point. Because the caller is about to free (and possibly reuse) those
1447	* blocks on-disk.
1448	*/
1449	void block_invalidatepage(struct page *page, unsigned int offset,
1450	unsigned int length)
1451	{
1452	struct buffer_head head, bh, *next;
1453	unsigned int curr_off = 0;
1454	unsigned int stop = length + offset;
1455
1456	BUG_ON(!PageLocked(page));
1457	if (!page_has_buffers(page))
1458	goto out;
1459
1460	/*
1461	* Check for overflow
1462	*/
1463	BUG_ON(stop > PAGE_SIZE \|\| stop < length);
1464
1465	head = page_buffers(page);
1466	bh = head;
1467	do {
1468	unsigned int next_off = curr_off + bh->b_size;
1469	next = bh->b_this_page;
1470
1471	/*
1472	* Are we still fully in range ?
1473	*/
1474	if (next_off > stop)
1475	goto out;
1476
1477	/*
1478	* is this block fully invalidated?
1479	*/
1480	if (offset <= curr_off)
1481	discard_buffer(bh);
1482	curr_off = next_off;
1483	bh = next;
1484	} while (bh != head);
1485
1486	/*
1487	* We release buffers only if the entire page is being invalidated.
1488	* The get_block cached value has been unconditionally invalidated,
1489	* so real IO is not possible anymore.
1490	*/
1491	if (length == PAGE_SIZE)
1492	try_to_release_page(page, 0);
1493	out:
1494	return;
1495	}
1496	EXPORT_SYMBOL(block_invalidatepage);
1497
1498
1499	/*
1500	* We attach and possibly dirty the buffers atomically wrt
1501	* __set_page_dirty_buffers() via private_lock. try_to_free_buffers
1502	* is already excluded via the page lock.
1503	*/
1504	void create_empty_buffers(struct page *page,
1505	unsigned long blocksize, unsigned long b_state)
1506	{
1507	struct buffer_head bh, head, *tail;
1508
1509	head = alloc_page_buffers(page, blocksize, true);
1510	bh = head;
1511	do {
1512	bh->b_state \|= b_state;
1513	tail = bh;
1514	bh = bh->b_this_page;
1515	} while (bh);
1516	tail->b_this_page = head;
1517
1518	spin_lock(&page->mapping->private_lock);
1519	if (PageUptodate(page) \|\| PageDirty(page)) {
1520	bh = head;
1521	do {
1522	if (PageDirty(page))
1523	set_buffer_dirty(bh);
1524	if (PageUptodate(page))
1525	set_buffer_uptodate(bh);
1526	bh = bh->b_this_page;
1527	} while (bh != head);
1528	}
1529	attach_page_buffers(page, head);
1530	spin_unlock(&page->mapping->private_lock);
1531	}
1532	EXPORT_SYMBOL(create_empty_buffers);
1533
1534	/**
1535	* clean_bdev_aliases: clean a range of buffers in block device
1536	* @bdev: Block device to clean buffers in
1537	* @block: Start of a range of blocks to clean
1538	* @len: Number of blocks to clean
1539	*
1540	* We are taking a range of blocks for data and we don't want writeback of any
1541	* buffer-cache aliases starting from return from this function and until the
1542	* moment when something will explicitly mark the buffer dirty (hopefully that
1543	* will not happen until we will free that block ;-) We don't even need to mark
1544	* it not-uptodate - nobody can expect anything from a newly allocated buffer
1545	* anyway. We used to use unmap_buffer() for such invalidation, but that was
1546	* wrong. We definitely don't want to mark the alias unmapped, for example - it
1547	* would confuse anyone who might pick it with bread() afterwards...
1548	*
1549	* Also.. Note that bforget() doesn't lock the buffer. So there can be
1550	* writeout I/O going on against recently-freed buffers. We don't wait on that
1551	* I/O in bforget() - it's more efficient to wait on the I/O only if we really
1552	* need to. That happens here.
1553	*/
1554	void clean_bdev_aliases(struct block_device *bdev, sector_t block, sector_t len)
1555	{
1556	struct inode *bd_inode = bdev->bd_inode;
1557	struct address_space *bd_mapping = bd_inode->i_mapping;
1558	struct pagevec pvec;
1559	pgoff_t index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
1560	pgoff_t end;
1561	int i, count;
1562	struct buffer_head *bh;
1563	struct buffer_head *head;
1564
1565	end = (block + len - 1) >> (PAGE_SHIFT - bd_inode->i_blkbits);
1566	pagevec_init(&pvec);
1567	while (pagevec_lookup_range(&pvec, bd_mapping, &index, end)) {
1568	count = pagevec_count(&pvec);
1569	for (i = 0; i < count; i++) {
1570	struct page *page = pvec.pages[i];
1571
1572	if (!page_has_buffers(page))
1573	continue;
1574	/*
1575	* We use page lock instead of bd_mapping->private_lock
1576	* to pin buffers here since we can afford to sleep and
1577	* it scales better than a global spinlock lock.
1578	*/
1579	lock_page(page);
1580	/* Recheck when the page is locked which pins bhs */
1581	if (!page_has_buffers(page))
1582	goto unlock_page;
1583	head = page_buffers(page);
1584	bh = head;
1585	do {
1586	if (!buffer_mapped(bh) \|\| (bh->b_blocknr < block))
1587	goto next;
1588	if (bh->b_blocknr >= block + len)
1589	break;
1590	clear_buffer_dirty(bh);
1591	wait_on_buffer(bh);
1592	clear_buffer_req(bh);
1593	next:
1594	bh = bh->b_this_page;
1595	} while (bh != head);
1596	unlock_page:
1597	unlock_page(page);
1598	}
1599	pagevec_release(&pvec);
1600	cond_resched();
1601	/* End of range already reached? */
1602	if (index > end \|\| !index)
1603	break;
1604	}
1605	}
1606	EXPORT_SYMBOL(clean_bdev_aliases);
1607
1608	/*
1609	* Size is a power-of-two in the range 512..PAGE_SIZE,
1610	* and the case we care about most is PAGE_SIZE.
1611	*
1612	* So this could possibly be written with those
1613	* constraints in mind (relevant mostly if some
1614	* architecture has a slow bit-scan instruction)
1615	*/
1616	static inline int block_size_bits(unsigned int blocksize)
1617	{
1618	return ilog2(blocksize);
1619	}
1620
1621	static struct buffer_head create_page_buffers(struct page page, struct inode *inode, unsigned int b_state)
1622	{
1623	BUG_ON(!PageLocked(page));
1624
1625	if (!page_has_buffers(page))
1626	create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
1627	b_state);
1628	return page_buffers(page);
1629	}
1630
1631	/*
1632	* NOTE! All mapped/uptodate combinations are valid:
1633	*
1634	* Mapped Uptodate Meaning
1635	*
1636	* No No "unknown" - must do get_block()
1637	* No Yes "hole" - zero-filled
1638	* Yes No "allocated" - allocated on disk, not read in
1639	* Yes Yes "valid" - allocated and up-to-date in memory.
1640	*
1641	* "Dirty" is valid only with the last case (mapped+uptodate).
1642	*/
1643
1644	/*
1645	* While block_write_full_page is writing back the dirty buffers under
1646	* the page lock, whoever dirtied the buffers may decide to clean them
1647	* again at any time. We handle that by only looking at the buffer
1648	* state inside lock_buffer().
1649	*
1650	* If block_write_full_page() is called for regular writeback
1651	* (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1652	* locked buffer. This only can happen if someone has written the buffer
1653	* directly, with submit_bh(). At the address_space level PageWriteback
1654	* prevents this contention from occurring.
1655	*
1656	* If block_write_full_page() is called with wbc->sync_mode ==
1657	* WB_SYNC_ALL, the writes are posted using REQ_SYNC; this
1658	* causes the writes to be flagged as synchronous writes.
1659	*/
1660	int __block_write_full_page(struct inode inode, struct page page,
1661	get_block_t get_block, struct writeback_control wbc,
1662	bh_end_io_t *handler)
1663	{
1664	int err;
1665	sector_t block;
1666	sector_t last_block;
1667	struct buffer_head bh, head;
1668	unsigned int blocksize, bbits;
1669	int nr_underway = 0;
1670	int write_flags = wbc_to_write_flags(wbc);
1671
1672	head = create_page_buffers(page, inode,
1673	(1 << BH_Dirty)\|(1 << BH_Uptodate));
1674
1675	/*
1676	* Be very careful. We have no exclusion from __set_page_dirty_buffers
1677	* here, and the (potentially unmapped) buffers may become dirty at
1678	* any time. If a buffer becomes dirty here after we've inspected it
1679	* then we just miss that fact, and the page stays dirty.
1680	*
1681	* Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1682	* handle that here by just cleaning them.
1683	*/
1684
1685	bh = head;
1686	blocksize = bh->b_size;
1687	bbits = block_size_bits(blocksize);
1688
1689	block = (sector_t)page->index << (PAGE_SHIFT - bbits);
1690	last_block = (i_size_read(inode) - 1) >> bbits;
1691
1692	/*
1693	* Get all the dirty buffers mapped to disk addresses and
1694	* handle any aliases from the underlying blockdev's mapping.
1695	*/
1696	do {
1697	if (block > last_block) {
1698	/*
1699	* mapped buffers outside i_size will occur, because
1700	* this page can be outside i_size when there is a
1701	* truncate in progress.
1702	*/
1703	/*
1704	* The buffer was zeroed by block_write_full_page()
1705	*/
1706	clear_buffer_dirty(bh);
1707	set_buffer_uptodate(bh);
1708	} else if ((!buffer_mapped(bh) \|\| buffer_delay(bh)) &&
1709	buffer_dirty(bh)) {
1710	WARN_ON(bh->b_size != blocksize);
1711	err = get_block(inode, block, bh, 1);
1712	if (err)
1713	goto recover;
1714	clear_buffer_delay(bh);
1715	if (buffer_new(bh)) {
1716	/* blockdev mappings never come here */
1717	clear_buffer_new(bh);
1718	clean_bdev_bh_alias(bh);
1719	}
1720	}
1721	bh = bh->b_this_page;
1722	block++;
1723	} while (bh != head);
1724
1725	do {
1726	if (!buffer_mapped(bh))
1727	continue;
1728	/*
1729	* If it's a fully non-blocking write attempt and we cannot
1730	* lock the buffer then redirty the page. Note that this can
1731	* potentially cause a busy-wait loop from writeback threads
1732	* and kswapd activity, but those code paths have their own
1733	* higher-level throttling.
1734	*/
1735	if (wbc->sync_mode != WB_SYNC_NONE) {
1736	lock_buffer(bh);
1737	} else if (!trylock_buffer(bh)) {
1738	redirty_page_for_writepage(wbc, page);
1739	continue;
1740	}
1741	if (test_clear_buffer_dirty(bh)) {
1742	mark_buffer_async_write_endio(bh, handler);
1743	} else {
1744	unlock_buffer(bh);
1745	}
1746	} while ((bh = bh->b_this_page) != head);
1747
1748	/*
1749	* The page and its buffers are protected by PageWriteback(), so we can
1750	* drop the bh refcounts early.
1751	*/
1752	BUG_ON(PageWriteback(page));
1753	set_page_writeback(page);
1754
1755	do {
1756	struct buffer_head *next = bh->b_this_page;
1757	if (buffer_async_write(bh)) {
1758	submit_bh_wbc(REQ_OP_WRITE, write_flags, bh,
1759	inode->i_write_hint, wbc);
1760	nr_underway++;
1761	}
1762	bh = next;
1763	} while (bh != head);
1764	unlock_page(page);
1765
1766	err = 0;
1767	done:
1768	if (nr_underway == 0) {
1769	/*
1770	* The page was marked dirty, but the buffers were
1771	* clean. Someone wrote them back by hand with
1772	* ll_rw_block/submit_bh. A rare case.
1773	*/
1774	end_page_writeback(page);
1775
1776	/*
1777	* The page and buffer_heads can be released at any time from
1778	* here on.
1779	*/
1780	}
1781	return err;
1782
1783	recover:
1784	/*
1785	* ENOSPC, or some other error. We may already have added some
1786	* blocks to the file, so we need to write these out to avoid
1787	* exposing stale data.
1788	* The page is currently locked and not marked for writeback
1789	*/
1790	bh = head;
1791	/* Recovery: lock and submit the mapped buffers */
1792	do {
1793	if (buffer_mapped(bh) && buffer_dirty(bh) &&
1794	!buffer_delay(bh)) {
1795	lock_buffer(bh);
1796	mark_buffer_async_write_endio(bh, handler);
1797	} else {
1798	/*
1799	* The buffer may have been set dirty during
1800	* attachment to a dirty page.
1801	*/
1802	clear_buffer_dirty(bh);
1803	}
1804	} while ((bh = bh->b_this_page) != head);
1805	SetPageError(page);
1806	BUG_ON(PageWriteback(page));
1807	mapping_set_error(page->mapping, err);
1808	set_page_writeback(page);
1809	do {
1810	struct buffer_head *next = bh->b_this_page;
1811	if (buffer_async_write(bh)) {
1812	clear_buffer_dirty(bh);
1813	submit_bh_wbc(REQ_OP_WRITE, write_flags, bh,
1814	inode->i_write_hint, wbc);
1815	nr_underway++;
1816	}
1817	bh = next;
1818	} while (bh != head);
1819	unlock_page(page);
1820	goto done;
1821	}
1822	EXPORT_SYMBOL(__block_write_full_page);
1823
1824	/*
1825	* If a page has any new buffers, zero them out here, and mark them uptodate
1826	* and dirty so they'll be written out (in order to prevent uninitialised
1827	* block data from leaking). And clear the new bit.
1828	*/
1829	void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1830	{
1831	unsigned int block_start, block_end;
1832	struct buffer_head head, bh;
1833
1834	BUG_ON(!PageLocked(page));
1835	if (!page_has_buffers(page))
1836	return;
1837
1838	bh = head = page_buffers(page);
1839	block_start = 0;
1840	do {
1841	block_end = block_start + bh->b_size;
1842
1843	if (buffer_new(bh)) {
1844	if (block_end > from && block_start < to) {
1845	if (!PageUptodate(page)) {
1846	unsigned start, size;
1847
1848	start = max(from, block_start);
1849	size = min(to, block_end) - start;
1850
1851	zero_user(page, start, size);
1852	set_buffer_uptodate(bh);
1853	}
1854
1855	clear_buffer_new(bh);
1856	mark_buffer_dirty(bh);
1857	}
1858	}
1859
1860	block_start = block_end;
1861	bh = bh->b_this_page;
1862	} while (bh != head);
1863	}
1864	EXPORT_SYMBOL(page_zero_new_buffers);
1865
1866	static void
1867	iomap_to_bh(struct inode inode, sector_t block, struct buffer_head bh,
1868	struct iomap *iomap)
1869	{
1870	loff_t offset = block << inode->i_blkbits;
1871
1872	bh->b_bdev = iomap->bdev;
1873
1874	/*
1875	* Block points to offset in file we need to map, iomap contains
1876	* the offset at which the map starts. If the map ends before the
1877	* current block, then do not map the buffer and let the caller
1878	* handle it.
1879	*/
1880	BUG_ON(offset >= iomap->offset + iomap->length);
1881
1882	switch (iomap->type) {
1883	case IOMAP_HOLE:
1884	/*
1885	* If the buffer is not up to date or beyond the current EOF,
1886	* we need to mark it as new to ensure sub-block zeroing is
1887	* executed if necessary.
1888	*/
1889	if (!buffer_uptodate(bh) \|\|
1890	(offset >= i_size_read(inode)))
1891	set_buffer_new(bh);
1892	break;
1893	case IOMAP_DELALLOC:
1894	if (!buffer_uptodate(bh) \|\|
1895	(offset >= i_size_read(inode)))
1896	set_buffer_new(bh);
1897	set_buffer_uptodate(bh);
1898	set_buffer_mapped(bh);
1899	set_buffer_delay(bh);
1900	break;
1901	case IOMAP_UNWRITTEN:
1902	/*
1903	* For unwritten regions, we always need to ensure that
1904	* sub-block writes cause the regions in the block we are not
1905	* writing to are zeroed. Set the buffer as new to ensure this.
1906	*/
1907	set_buffer_new(bh);
1908	set_buffer_unwritten(bh);
1909	/* FALLTHRU */
1910	case IOMAP_MAPPED:
1911	if (offset >= i_size_read(inode))
1912	set_buffer_new(bh);
1913	bh->b_blocknr = (iomap->addr + offset - iomap->offset) >>
1914	inode->i_blkbits;
1915	set_buffer_mapped(bh);
1916	break;
1917	}
1918	}
1919
1920	int __block_write_begin_int(struct page *page, loff_t pos, unsigned len,
1921	get_block_t get_block, struct iomap iomap)
1922	{
1923	unsigned from = pos & (PAGE_SIZE - 1);
1924	unsigned to = from + len;
1925	struct inode *inode = page->mapping->host;
1926	unsigned block_start, block_end;
1927	sector_t block;
1928	int err = 0;
1929	unsigned blocksize, bbits;
1930	struct buffer_head bh, head, wait[2], *wait_bh=wait;
1931
1932	BUG_ON(!PageLocked(page));
1933	BUG_ON(from > PAGE_SIZE);
1934	BUG_ON(to > PAGE_SIZE);
1935	BUG_ON(from > to);
1936
1937	head = create_page_buffers(page, inode, 0);
1938	blocksize = head->b_size;
1939	bbits = block_size_bits(blocksize);
1940
1941	block = (sector_t)page->index << (PAGE_SHIFT - bbits);
1942
1943	for(bh = head, block_start = 0; bh != head \|\| !block_start;
1944	block++, block_start=block_end, bh = bh->b_this_page) {
1945	block_end = block_start + blocksize;
1946	if (block_end <= from \|\| block_start >= to) {
1947	if (PageUptodate(page)) {
1948	if (!buffer_uptodate(bh))
1949	set_buffer_uptodate(bh);
1950	}
1951	continue;
1952	}
1953	if (buffer_new(bh))
1954	clear_buffer_new(bh);
1955	if (!buffer_mapped(bh)) {
1956	WARN_ON(bh->b_size != blocksize);
1957	if (get_block) {
1958	err = get_block(inode, block, bh, 1);
1959	if (err)
1960	break;
1961	} else {
1962	iomap_to_bh(inode, block, bh, iomap);
1963	}
1964
1965	if (buffer_new(bh)) {
1966	clean_bdev_bh_alias(bh);
1967	if (PageUptodate(page)) {
1968	clear_buffer_new(bh);
1969	set_buffer_uptodate(bh);
1970	mark_buffer_dirty(bh);
1971	continue;
1972	}
1973	if (block_end > to \|\| block_start < from)
1974	zero_user_segments(page,
1975	to, block_end,
1976	block_start, from);
1977	continue;
1978	}
1979	}
1980	if (PageUptodate(page)) {
1981	if (!buffer_uptodate(bh))
1982	set_buffer_uptodate(bh);
1983	continue;
1984	}
1985	if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
1986	!buffer_unwritten(bh) &&
1987	(block_start < from \|\| block_end > to)) {
1988	ll_rw_block(REQ_OP_READ, 0, 1, &bh);
1989	*wait_bh++=bh;
1990	}
1991	}
1992	/*
1993	* If we issued read requests - let them complete.
1994	*/
1995	while(wait_bh > wait) {
1996	wait_on_buffer(*--wait_bh);
1997	if (!buffer_uptodate(*wait_bh))
1998	err = -EIO;
1999	}
2000	if (unlikely(err))
2001	page_zero_new_buffers(page, from, to);
2002	return err;
2003	}
2004
2005	int __block_write_begin(struct page *page, loff_t pos, unsigned len,
2006	get_block_t *get_block)
2007	{
2008	return __block_write_begin_int(page, pos, len, get_block, NULL);
2009	}
2010	EXPORT_SYMBOL(__block_write_begin);
2011
2012	static int __block_commit_write(struct inode inode, struct page page,
2013	unsigned from, unsigned to)
2014	{
2015	unsigned block_start, block_end;
2016	int partial = 0;
2017	unsigned blocksize;
2018	struct buffer_head bh, head;
2019
2020	bh = head = page_buffers(page);
2021	blocksize = bh->b_size;
2022
2023	block_start = 0;
2024	do {
2025	block_end = block_start + blocksize;
2026	if (block_end <= from \|\| block_start >= to) {
2027	if (!buffer_uptodate(bh))
2028	partial = 1;
2029	} else {
2030	set_buffer_uptodate(bh);
2031	mark_buffer_dirty(bh);
2032	}
2033	clear_buffer_new(bh);
2034
2035	block_start = block_end;
2036	bh = bh->b_this_page;
2037	} while (bh != head);
2038
2039	/*
2040	* If this is a partial write which happened to make all buffers
2041	* uptodate then we can optimize away a bogus readpage() for
2042	* the next read(). Here we 'discover' whether the page went
2043	* uptodate as a result of this (potentially partial) write.
2044	*/
2045	if (!partial)
2046	SetPageUptodate(page);
2047	return 0;
2048	}
2049
2050	/*
2051	* block_write_begin takes care of the basic task of block allocation and
2052	* bringing partial write blocks uptodate first.
2053	*
2054	* The filesystem needs to handle block truncation upon failure.
2055	*/
2056	int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
2057	unsigned flags, struct page *pagep, get_block_t get_block)
2058	{
2059	pgoff_t index = pos >> PAGE_SHIFT;
2060	struct page *page;
2061	int status;
2062
2063	page = grab_cache_page_write_begin(mapping, index, flags);
2064	if (!page)
2065	return -ENOMEM;
2066
2067	status = __block_write_begin(page, pos, len, get_block);
2068	if (unlikely(status)) {
2069	unlock_page(page);
2070	put_page(page);
2071	page = NULL;
2072	}
2073
2074	*pagep = page;
2075	return status;
2076	}
2077	EXPORT_SYMBOL(block_write_begin);
2078
2079	int block_write_end(struct file file, struct address_space mapping,
2080	loff_t pos, unsigned len, unsigned copied,
2081	struct page page, void fsdata)
2082	{
2083	struct inode *inode = mapping->host;
2084	unsigned start;
2085
2086	start = pos & (PAGE_SIZE - 1);
2087
2088	if (unlikely(copied < len)) {
2089	/*
2090	* The buffers that were written will now be uptodate, so we
2091	* don't have to worry about a readpage reading them and
2092	* overwriting a partial write. However if we have encountered
2093	* a short write and only partially written into a buffer, it
2094	* will not be marked uptodate, so a readpage might come in and
2095	* destroy our partial write.
2096	*
2097	* Do the simplest thing, and just treat any short write to a
2098	* non uptodate page as a zero-length write, and force the
2099	* caller to redo the whole thing.
2100	*/
2101	if (!PageUptodate(page))
2102	copied = 0;
2103
2104	page_zero_new_buffers(page, start+copied, start+len);
2105	}
2106	flush_dcache_page(page);
2107
2108	/* This could be a short (even 0-length) commit */
2109	__block_commit_write(inode, page, start, start+copied);
2110
2111	return copied;
2112	}
2113	EXPORT_SYMBOL(block_write_end);
2114
2115	int generic_write_end(struct file file, struct address_space mapping,
2116	loff_t pos, unsigned len, unsigned copied,
2117	struct page page, void fsdata)
2118	{
2119	struct inode *inode = mapping->host;
2120	loff_t old_size = inode->i_size;
2121	int i_size_changed = 0;
2122
2123	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2124
2125	/*
2126	* No need to use i_size_read() here, the i_size
2127	* cannot change under us because we hold i_mutex.
2128	*
2129	* But it's important to update i_size while still holding page lock:
2130	* page writeout could otherwise come in and zero beyond i_size.
2131	*/
2132	if (pos+copied > inode->i_size) {
2133	i_size_write(inode, pos+copied);
2134	i_size_changed = 1;
2135	}
2136
2137	unlock_page(page);
2138	put_page(page);
2139
2140	if (old_size < pos)
2141	pagecache_isize_extended(inode, old_size, pos);
2142	/*
2143	* Don't mark the inode dirty under page lock. First, it unnecessarily
2144	* makes the holding time of page lock longer. Second, it forces lock
2145	* ordering of page lock and transaction start for journaling
2146	* filesystems.
2147	*/
2148	if (i_size_changed)
2149	mark_inode_dirty(inode);
2150
2151	return copied;
2152	}
2153	EXPORT_SYMBOL(generic_write_end);
2154
2155	/*
2156	* block_is_partially_uptodate checks whether buffers within a page are
2157	* uptodate or not.
2158	*
2159	* Returns true if all buffers which correspond to a file portion
2160	* we want to read are uptodate.
2161	*/
2162	int block_is_partially_uptodate(struct page *page, unsigned long from,
2163	unsigned long count)
2164	{
2165	unsigned block_start, block_end, blocksize;
2166	unsigned to;
2167	struct buffer_head bh, head;
2168	int ret = 1;
2169
2170	if (!page_has_buffers(page))
2171	return 0;
2172
2173	head = page_buffers(page);
2174	blocksize = head->b_size;
2175	to = min_t(unsigned, PAGE_SIZE - from, count);
2176	to = from + to;
2177	if (from < blocksize && to > PAGE_SIZE - blocksize)
2178	return 0;
2179
2180	bh = head;
2181	block_start = 0;
2182	do {
2183	block_end = block_start + blocksize;
2184	if (block_end > from && block_start < to) {
2185	if (!buffer_uptodate(bh)) {
2186	ret = 0;
2187	break;
2188	}
2189	if (block_end >= to)
2190	break;
2191	}
2192	block_start = block_end;
2193	bh = bh->b_this_page;
2194	} while (bh != head);
2195
2196	return ret;
2197	}
2198	EXPORT_SYMBOL(block_is_partially_uptodate);
2199
2200	/*
2201	* Generic "read page" function for block devices that have the normal
2202	* get_block functionality. This is most of the block device filesystems.
2203	* Reads the page asynchronously --- the unlock_buffer() and
2204	* set/clear_buffer_uptodate() functions propagate buffer state into the
2205	* page struct once IO has completed.
2206	*/
2207	int block_read_full_page(struct page page, get_block_t get_block)
2208	{
2209	struct inode *inode = page->mapping->host;
2210	sector_t iblock, lblock;
2211	struct buffer_head bh, head, *arr[MAX_BUF_PER_PAGE];
2212	unsigned int blocksize, bbits;
2213	int nr, i;
2214	int fully_mapped = 1;
2215
2216	head = create_page_buffers(page, inode, 0);
2217	blocksize = head->b_size;
2218	bbits = block_size_bits(blocksize);
2219
2220	iblock = (sector_t)page->index << (PAGE_SHIFT - bbits);
2221	lblock = (i_size_read(inode)+blocksize-1) >> bbits;
2222	bh = head;
2223	nr = 0;
2224	i = 0;
2225
2226	do {
2227	if (buffer_uptodate(bh))
2228	continue;
2229
2230	if (!buffer_mapped(bh)) {
2231	int err = 0;
2232
2233	fully_mapped = 0;
2234	if (iblock < lblock) {
2235	WARN_ON(bh->b_size != blocksize);
2236	err = get_block(inode, iblock, bh, 0);
2237	if (err)
2238	SetPageError(page);
2239	}
2240	if (!buffer_mapped(bh)) {
2241	zero_user(page, i * blocksize, blocksize);
2242	if (!err)
2243	set_buffer_uptodate(bh);
2244	continue;
2245	}
2246	/*
2247	* get_block() might have updated the buffer
2248	* synchronously
2249	*/
2250	if (buffer_uptodate(bh))
2251	continue;
2252	}
2253	arr[nr++] = bh;
2254	} while (i++, iblock++, (bh = bh->b_this_page) != head);
2255
2256	if (fully_mapped)
2257	SetPageMappedToDisk(page);
2258
2259	if (!nr) {
2260	/*
2261	* All buffers are uptodate - we can set the page uptodate
2262	* as well. But not if get_block() returned an error.
2263	*/
2264	if (!PageError(page))
2265	SetPageUptodate(page);
2266	unlock_page(page);
2267	return 0;
2268	}
2269
2270	/* Stage two: lock the buffers */
2271	for (i = 0; i < nr; i++) {
2272	bh = arr[i];
2273	lock_buffer(bh);
2274	mark_buffer_async_read(bh);
2275	}
2276
2277	/*
2278	* Stage 3: start the IO. Check for uptodateness
2279	* inside the buffer lock in case another process reading
2280	* the underlying blockdev brought it uptodate (the sct fix).
2281	*/
2282	for (i = 0; i < nr; i++) {
2283	bh = arr[i];
2284	if (buffer_uptodate(bh))
2285	end_buffer_async_read(bh, 1);
2286	else
2287	submit_bh(REQ_OP_READ, 0, bh);
2288	}
2289	return 0;
2290	}
2291	EXPORT_SYMBOL(block_read_full_page);
2292
2293	/* utility function for filesystems that need to do work on expanding
2294	* truncates. Uses filesystem pagecache writes to allow the filesystem to
2295	* deal with the hole.
2296	*/
2297	int generic_cont_expand_simple(struct inode *inode, loff_t size)
2298	{
2299	struct address_space *mapping = inode->i_mapping;
2300	struct page *page;
2301	void *fsdata;
2302	int err;
2303
2304	err = inode_newsize_ok(inode, size);
2305	if (err)
2306	goto out;
2307
2308	err = pagecache_write_begin(NULL, mapping, size, 0,
2309	AOP_FLAG_CONT_EXPAND, &page, &fsdata);
2310	if (err)
2311	goto out;
2312
2313	err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
2314	BUG_ON(err > 0);
2315
2316	out:
2317	return err;
2318	}
2319	EXPORT_SYMBOL(generic_cont_expand_simple);
2320
2321	static int cont_expand_zero(struct file file, struct address_space mapping,
2322	loff_t pos, loff_t *bytes)
2323	{
2324	struct inode *inode = mapping->host;
2325	unsigned int blocksize = i_blocksize(inode);
2326	struct page *page;
2327	void *fsdata;
2328	pgoff_t index, curidx;
2329	loff_t curpos;
2330	unsigned zerofrom, offset, len;
2331	int err = 0;
2332
2333	index = pos >> PAGE_SHIFT;
2334	offset = pos & ~PAGE_MASK;
2335
2336	while (index > (curidx = (curpos = *bytes)>>PAGE_SHIFT)) {
2337	zerofrom = curpos & ~PAGE_MASK;
2338	if (zerofrom & (blocksize-1)) {
2339	*bytes \|= (blocksize-1);
2340	(*bytes)++;
2341	}
2342	len = PAGE_SIZE - zerofrom;
2343
2344	err = pagecache_write_begin(file, mapping, curpos, len, 0,
2345	&page, &fsdata);
2346	if (err)
2347	goto out;
2348	zero_user(page, zerofrom, len);
2349	err = pagecache_write_end(file, mapping, curpos, len, len,
2350	page, fsdata);
2351	if (err < 0)
2352	goto out;
2353	BUG_ON(err != len);
2354	err = 0;
2355
2356	balance_dirty_pages_ratelimited(mapping);
2357
2358	if (unlikely(fatal_signal_pending(current))) {
2359	err = -EINTR;
2360	goto out;
2361	}
2362	}
2363
2364	/* page covers the boundary, find the boundary offset */
2365	if (index == curidx) {
2366	zerofrom = curpos & ~PAGE_MASK;
2367	/* if we will expand the thing last block will be filled */
2368	if (offset <= zerofrom) {
2369	goto out;
2370	}
2371	if (zerofrom & (blocksize-1)) {
2372	*bytes \|= (blocksize-1);
2373	(*bytes)++;
2374	}
2375	len = offset - zerofrom;
2376
2377	err = pagecache_write_begin(file, mapping, curpos, len, 0,
2378	&page, &fsdata);
2379	if (err)
2380	goto out;
2381	zero_user(page, zerofrom, len);
2382	err = pagecache_write_end(file, mapping, curpos, len, len,
2383	page, fsdata);
2384	if (err < 0)
2385	goto out;
2386	BUG_ON(err != len);
2387	err = 0;
2388	}
2389	out:
2390	return err;
2391	}
2392
2393	/*
2394	* For moronic filesystems that do not allow holes in file.
2395	* We may have to extend the file.
2396	*/
2397	int cont_write_begin(struct file file, struct address_space mapping,
2398	loff_t pos, unsigned len, unsigned flags,
2399	struct page pagep, void fsdata,
2400	get_block_t get_block, loff_t bytes)
2401	{
2402	struct inode *inode = mapping->host;
2403	unsigned int blocksize = i_blocksize(inode);
2404	unsigned int zerofrom;
2405	int err;
2406
2407	err = cont_expand_zero(file, mapping, pos, bytes);
2408	if (err)
2409	return err;
2410
2411	zerofrom = *bytes & ~PAGE_MASK;
2412	if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2413	*bytes \|= (blocksize-1);
2414	(*bytes)++;
2415	}
2416
2417	return block_write_begin(mapping, pos, len, flags, pagep, get_block);
2418	}
2419	EXPORT_SYMBOL(cont_write_begin);
2420
2421	int block_commit_write(struct page *page, unsigned from, unsigned to)
2422	{
2423	struct inode *inode = page->mapping->host;
2424	__block_commit_write(inode,page,from,to);
2425	return 0;
2426	}
2427	EXPORT_SYMBOL(block_commit_write);
2428
2429	/*
2430	* block_page_mkwrite() is not allowed to change the file size as it gets
2431	* called from a page fault handler when a page is first dirtied. Hence we must
2432	* be careful to check for EOF conditions here. We set the page up correctly
2433	* for a written page which means we get ENOSPC checking when writing into
2434	* holes and correct delalloc and unwritten extent mapping on filesystems that
2435	* support these features.
2436	*
2437	* We are not allowed to take the i_mutex here so we have to play games to
2438	* protect against truncate races as the page could now be beyond EOF. Because
2439	* truncate writes the inode size before removing pages, once we have the
2440	* page lock we can determine safely if the page is beyond EOF. If it is not
2441	* beyond EOF, then the page is guaranteed safe against truncation until we
2442	* unlock the page.
2443	*
2444	* Direct callers of this function should protect against filesystem freezing
2445	* using sb_start_pagefault() - sb_end_pagefault() functions.
2446	*/
2447	int block_page_mkwrite(struct vm_area_struct vma, struct vm_fault vmf,
2448	get_block_t get_block)
2449	{
2450	struct page *page = vmf->page;
2451	struct inode *inode = file_inode(vma->vm_file);
2452	unsigned long end;
2453	loff_t size;
2454	int ret;
2455
2456	lock_page(page);
2457	size = i_size_read(inode);
2458	if ((page->mapping != inode->i_mapping) \|\|
2459	(page_offset(page) > size)) {
2460	/* We overload EFAULT to mean page got truncated */
2461	ret = -EFAULT;
2462	goto out_unlock;
2463	}
2464
2465	/* page is wholly or partially inside EOF */
2466	if (((page->index + 1) << PAGE_SHIFT) > size)
2467	end = size & ~PAGE_MASK;
2468	else
2469	end = PAGE_SIZE;
2470
2471	ret = __block_write_begin(page, 0, end, get_block);
2472	if (!ret)
2473	ret = block_commit_write(page, 0, end);
2474
2475	if (unlikely(ret < 0))
2476	goto out_unlock;
2477	set_page_dirty(page);
2478	wait_for_stable_page(page);
2479	return 0;
2480	out_unlock:
2481	unlock_page(page);
2482	return ret;
2483	}
2484	EXPORT_SYMBOL(block_page_mkwrite);
2485
2486	/*
2487	* nobh_write_begin()'s prereads are special: the buffer_heads are freed
2488	* immediately, while under the page lock. So it needs a special end_io
2489	* handler which does not touch the bh after unlocking it.
2490	*/
2491	static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2492	{
2493	__end_buffer_read_notouch(bh, uptodate);
2494	}
2495
2496	/*
2497	* Attach the singly-linked list of buffers created by nobh_write_begin, to
2498	* the page (converting it to circular linked list and taking care of page
2499	* dirty races).
2500	*/
2501	static void attach_nobh_buffers(struct page page, struct buffer_head head)
2502	{
2503	struct buffer_head *bh;
2504
2505	BUG_ON(!PageLocked(page));
2506
2507	spin_lock(&page->mapping->private_lock);
2508	bh = head;
2509	do {
2510	if (PageDirty(page))
2511	set_buffer_dirty(bh);
2512	if (!bh->b_this_page)
2513	bh->b_this_page = head;
2514	bh = bh->b_this_page;
2515	} while (bh != head);
2516	attach_page_buffers(page, head);
2517	spin_unlock(&page->mapping->private_lock);
2518	}
2519
2520	/*
2521	* On entry, the page is fully not uptodate.
2522	* On exit the page is fully uptodate in the areas outside (from,to)
2523	* The filesystem needs to handle block truncation upon failure.
2524	*/
2525	int nobh_write_begin(struct address_space *mapping,
2526	loff_t pos, unsigned len, unsigned flags,
2527	struct page pagep, void fsdata,
2528	get_block_t *get_block)
2529	{
2530	struct inode *inode = mapping->host;
2531	const unsigned blkbits = inode->i_blkbits;
2532	const unsigned blocksize = 1 << blkbits;
2533	struct buffer_head head, bh;
2534	struct page *page;
2535	pgoff_t index;
2536	unsigned from, to;
2537	unsigned block_in_page;
2538	unsigned block_start, block_end;
2539	sector_t block_in_file;
2540	int nr_reads = 0;
2541	int ret = 0;
2542	int is_mapped_to_disk = 1;
2543
2544	index = pos >> PAGE_SHIFT;
2545	from = pos & (PAGE_SIZE - 1);
2546	to = from + len;
2547
2548	page = grab_cache_page_write_begin(mapping, index, flags);
2549	if (!page)
2550	return -ENOMEM;
2551	*pagep = page;
2552	*fsdata = NULL;
2553
2554	if (page_has_buffers(page)) {
2555	ret = __block_write_begin(page, pos, len, get_block);
2556	if (unlikely(ret))
2557	goto out_release;
2558	return ret;
2559	}
2560
2561	if (PageMappedToDisk(page))
2562	return 0;
2563
2564	/*
2565	* Allocate buffers so that we can keep track of state, and potentially
2566	* attach them to the page if an error occurs. In the common case of
2567	* no error, they will just be freed again without ever being attached
2568	* to the page (which is all OK, because we're under the page lock).
2569	*
2570	* Be careful: the buffer linked list is a NULL terminated one, rather
2571	* than the circular one we're used to.
2572	*/
2573	head = alloc_page_buffers(page, blocksize, false);
2574	if (!head) {
2575	ret = -ENOMEM;
2576	goto out_release;
2577	}
2578
2579	block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
2580
2581	/*
2582	* We loop across all blocks in the page, whether or not they are
2583	* part of the affected region. This is so we can discover if the
2584	* page is fully mapped-to-disk.
2585	*/
2586	for (block_start = 0, block_in_page = 0, bh = head;
2587	block_start < PAGE_SIZE;
2588	block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2589	int create;
2590
2591	block_end = block_start + blocksize;
2592	bh->b_state = 0;
2593	create = 1;
2594	if (block_start >= to)
2595	create = 0;
2596	ret = get_block(inode, block_in_file + block_in_page,
2597	bh, create);
2598	if (ret)
2599	goto failed;
2600	if (!buffer_mapped(bh))
2601	is_mapped_to_disk = 0;
2602	if (buffer_new(bh))
2603	clean_bdev_bh_alias(bh);
2604	if (PageUptodate(page)) {
2605	set_buffer_uptodate(bh);
2606	continue;
2607	}
2608	if (buffer_new(bh) \|\| !buffer_mapped(bh)) {
2609	zero_user_segments(page, block_start, from,
2610	to, block_end);
2611	continue;
2612	}
2613	if (buffer_uptodate(bh))
2614	continue; /* reiserfs does this */
2615	if (block_start < from \|\| block_end > to) {
2616	lock_buffer(bh);
2617	bh->b_end_io = end_buffer_read_nobh;
2618	submit_bh(REQ_OP_READ, 0, bh);
2619	nr_reads++;
2620	}
2621	}
2622
2623	if (nr_reads) {
2624	/*
2625	* The page is locked, so these buffers are protected from
2626	* any VM or truncate activity. Hence we don't need to care
2627	* for the buffer_head refcounts.
2628	*/
2629	for (bh = head; bh; bh = bh->b_this_page) {
2630	wait_on_buffer(bh);
2631	if (!buffer_uptodate(bh))
2632	ret = -EIO;
2633	}
2634	if (ret)
2635	goto failed;
2636	}
2637
2638	if (is_mapped_to_disk)
2639	SetPageMappedToDisk(page);
2640
2641	fsdata = head; / to be released by nobh_write_end */
2642
2643	return 0;
2644
2645	failed:
2646	BUG_ON(!ret);
2647	/*
2648	* Error recovery is a bit difficult. We need to zero out blocks that
2649	* were newly allocated, and dirty them to ensure they get written out.
2650	* Buffers need to be attached to the page at this point, otherwise
2651	* the handling of potential IO errors during writeout would be hard
2652	* (could try doing synchronous writeout, but what if that fails too?)
2653	*/
2654	attach_nobh_buffers(page, head);
2655	page_zero_new_buffers(page, from, to);
2656
2657	out_release:
2658	unlock_page(page);
2659	put_page(page);
2660	*pagep = NULL;
2661
2662	return ret;
2663	}
2664	EXPORT_SYMBOL(nobh_write_begin);
2665
2666	int nobh_write_end(struct file file, struct address_space mapping,
2667	loff_t pos, unsigned len, unsigned copied,
2668	struct page page, void fsdata)
2669	{
2670	struct inode *inode = page->mapping->host;
2671	struct buffer_head *head = fsdata;
2672	struct buffer_head *bh;
2673	BUG_ON(fsdata != NULL && page_has_buffers(page));
2674
2675	if (unlikely(copied < len) && head)
2676	attach_nobh_buffers(page, head);
2677	if (page_has_buffers(page))
2678	return generic_write_end(file, mapping, pos, len,
2679	copied, page, fsdata);
2680
2681	SetPageUptodate(page);
2682	set_page_dirty(page);
2683	if (pos+copied > inode->i_size) {
2684	i_size_write(inode, pos+copied);
2685	mark_inode_dirty(inode);
2686	}
2687
2688	unlock_page(page);
2689	put_page(page);
2690
2691	while (head) {
2692	bh = head;
2693	head = head->b_this_page;
2694	free_buffer_head(bh);
2695	}
2696
2697	return copied;
2698	}
2699	EXPORT_SYMBOL(nobh_write_end);
2700
2701	/*
2702	* nobh_writepage() - based on block_full_write_page() except
2703	* that it tries to operate without attaching bufferheads to
2704	* the page.
2705	*/
2706	int nobh_writepage(struct page page, get_block_t get_block,
2707	struct writeback_control *wbc)
2708	{
2709	struct inode * const inode = page->mapping->host;
2710	loff_t i_size = i_size_read(inode);
2711	const pgoff_t end_index = i_size >> PAGE_SHIFT;
2712	unsigned offset;
2713	int ret;
2714
2715	/* Is the page fully inside i_size? */
2716	if (page->index < end_index)
2717	goto out;
2718
2719	/* Is the page fully outside i_size? (truncate in progress) */
2720	offset = i_size & (PAGE_SIZE-1);
2721	if (page->index >= end_index+1 \|\| !offset) {
2722	/*
2723	* The page may have dirty, unmapped buffers. For example,
2724	* they may have been added in ext3_writepage(). Make them
2725	* freeable here, so the page does not leak.
2726	*/
2727	#if 0
2728	/* Not really sure about this - do we need this ? */
2729	if (page->mapping->a_ops->invalidatepage)
2730	page->mapping->a_ops->invalidatepage(page, offset);
2731	#endif
2732	unlock_page(page);
2733	return 0; /* don't care */
2734	}
2735
2736	/*
2737	* The page straddles i_size. It must be zeroed out on each and every
2738	* writepage invocation because it may be mmapped. "A file is mapped
2739	* in multiples of the page size. For a file that is not a multiple of
2740	* the page size, the remaining memory is zeroed when mapped, and
2741	* writes to that region are not written out to the file."
2742	*/
2743	zero_user_segment(page, offset, PAGE_SIZE);
2744	out:
2745	ret = mpage_writepage(page, get_block, wbc);
2746	if (ret == -EAGAIN)
2747	ret = __block_write_full_page(inode, page, get_block, wbc,
2748	end_buffer_async_write);
2749	return ret;
2750	}
2751	EXPORT_SYMBOL(nobh_writepage);
2752
2753	int nobh_truncate_page(struct address_space *mapping,
2754	loff_t from, get_block_t *get_block)
2755	{
2756	pgoff_t index = from >> PAGE_SHIFT;
2757	unsigned offset = from & (PAGE_SIZE-1);
2758	unsigned blocksize;
2759	sector_t iblock;
2760	unsigned length, pos;
2761	struct inode *inode = mapping->host;
2762	struct page *page;
2763	struct buffer_head map_bh;
2764	int err;
2765
2766	blocksize = i_blocksize(inode);
2767	length = offset & (blocksize - 1);
2768
2769	/* Block boundary? Nothing to do */
2770	if (!length)
2771	return 0;
2772
2773	length = blocksize - length;
2774	iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
2775
2776	page = grab_cache_page(mapping, index);
2777	err = -ENOMEM;
2778	if (!page)
2779	goto out;
2780
2781	if (page_has_buffers(page)) {
2782	has_buffers:
2783	unlock_page(page);
2784	put_page(page);
2785	return block_truncate_page(mapping, from, get_block);
2786	}
2787
2788	/* Find the buffer that contains "offset" */
2789	pos = blocksize;
2790	while (offset >= pos) {
2791	iblock++;
2792	pos += blocksize;
2793	}
2794
2795	map_bh.b_size = blocksize;
2796	map_bh.b_state = 0;
2797	err = get_block(inode, iblock, &map_bh, 0);
2798	if (err)
2799	goto unlock;
2800	/* unmapped? It's a hole - nothing to do */
2801	if (!buffer_mapped(&map_bh))
2802	goto unlock;
2803
2804	/* Ok, it's mapped. Make sure it's up-to-date */
2805	if (!PageUptodate(page)) {
2806	err = mapping->a_ops->readpage(NULL, page);
2807	if (err) {
2808	put_page(page);
2809	goto out;
2810	}
2811	lock_page(page);
2812	if (!PageUptodate(page)) {
2813	err = -EIO;
2814	goto unlock;
2815	}
2816	if (page_has_buffers(page))
2817	goto has_buffers;
2818	}
2819	zero_user(page, offset, length);
2820	set_page_dirty(page);
2821	err = 0;
2822
2823	unlock:
2824	unlock_page(page);
2825	put_page(page);
2826	out:
2827	return err;
2828	}
2829	EXPORT_SYMBOL(nobh_truncate_page);
2830
2831	int block_truncate_page(struct address_space *mapping,
2832	loff_t from, get_block_t *get_block)
2833	{
2834	pgoff_t index = from >> PAGE_SHIFT;
2835	unsigned offset = from & (PAGE_SIZE-1);
2836	unsigned blocksize;
2837	sector_t iblock;
2838	unsigned length, pos;
2839	struct inode *inode = mapping->host;
2840	struct page *page;
2841	struct buffer_head *bh;
2842	int err;
2843
2844	blocksize = i_blocksize(inode);
2845	length = offset & (blocksize - 1);
2846
2847	/* Block boundary? Nothing to do */
2848	if (!length)
2849	return 0;
2850
2851	length = blocksize - length;
2852	iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
2853
2854	page = grab_cache_page(mapping, index);
2855	err = -ENOMEM;
2856	if (!page)
2857	goto out;
2858
2859	if (!page_has_buffers(page))
2860	create_empty_buffers(page, blocksize, 0);
2861
2862	/* Find the buffer that contains "offset" */
2863	bh = page_buffers(page);
2864	pos = blocksize;
2865	while (offset >= pos) {
2866	bh = bh->b_this_page;
2867	iblock++;
2868	pos += blocksize;
2869	}
2870
2871	err = 0;
2872	if (!buffer_mapped(bh)) {
2873	WARN_ON(bh->b_size != blocksize);
2874	err = get_block(inode, iblock, bh, 0);
2875	if (err)
2876	goto unlock;
2877	/* unmapped? It's a hole - nothing to do */
2878	if (!buffer_mapped(bh))
2879	goto unlock;
2880	}
2881
2882	/* Ok, it's mapped. Make sure it's up-to-date */
2883	if (PageUptodate(page))
2884	set_buffer_uptodate(bh);
2885
2886	if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2887	err = -EIO;
2888	ll_rw_block(REQ_OP_READ, 0, 1, &bh);
2889	wait_on_buffer(bh);
2890	/* Uhhuh. Read error. Complain and punt. */
2891	if (!buffer_uptodate(bh))
2892	goto unlock;
2893	}
2894
2895	zero_user(page, offset, length);
2896	mark_buffer_dirty(bh);
2897	err = 0;
2898
2899	unlock:
2900	unlock_page(page);
2901	put_page(page);
2902	out:
2903	return err;
2904	}
2905	EXPORT_SYMBOL(block_truncate_page);
2906
2907	/*
2908	* The generic ->writepage function for buffer-backed address_spaces
2909	*/
2910	int block_write_full_page(struct page page, get_block_t get_block,
2911	struct writeback_control *wbc)
2912	{
2913	struct inode * const inode = page->mapping->host;
2914	loff_t i_size = i_size_read(inode);
2915	const pgoff_t end_index = i_size >> PAGE_SHIFT;
2916	unsigned offset;
2917
2918	/* Is the page fully inside i_size? */
2919	if (page->index < end_index)
2920	return __block_write_full_page(inode, page, get_block, wbc,
2921	end_buffer_async_write);
2922
2923	/* Is the page fully outside i_size? (truncate in progress) */
2924	offset = i_size & (PAGE_SIZE-1);
2925	if (page->index >= end_index+1 \|\| !offset) {
2926	/*
2927	* The page may have dirty, unmapped buffers. For example,
2928	* they may have been added in ext3_writepage(). Make them
2929	* freeable here, so the page does not leak.
2930	*/
2931	do_invalidatepage(page, 0, PAGE_SIZE);
2932	unlock_page(page);
2933	return 0; /* don't care */
2934	}
2935
2936	/*
2937	* The page straddles i_size. It must be zeroed out on each and every
2938	* writepage invocation because it may be mmapped. "A file is mapped
2939	* in multiples of the page size. For a file that is not a multiple of
2940	* the page size, the remaining memory is zeroed when mapped, and
2941	* writes to that region are not written out to the file."
2942	*/
2943	zero_user_segment(page, offset, PAGE_SIZE);
2944	return __block_write_full_page(inode, page, get_block, wbc,
2945	end_buffer_async_write);
2946	}
2947	EXPORT_SYMBOL(block_write_full_page);
2948
2949	sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2950	get_block_t *get_block)
2951	{
2952	struct inode *inode = mapping->host;
2953	struct buffer_head tmp = {
2954	.b_size = i_blocksize(inode),
2955	};
2956
2957	get_block(inode, block, &tmp, 0);
2958	return tmp.b_blocknr;
2959	}
2960	EXPORT_SYMBOL(generic_block_bmap);
2961
2962	static void end_bio_bh_io_sync(struct bio *bio)
2963	{
2964	struct buffer_head *bh = bio->bi_private;
2965
2966	if (unlikely(bio_flagged(bio, BIO_QUIET)))
2967	set_bit(BH_Quiet, &bh->b_state);
2968
2969	bh->b_end_io(bh, !bio->bi_status);
2970	bio_put(bio);
2971	}
2972
2973	/*
2974	* This allows us to do IO even on the odd last sectors
2975	* of a device, even if the block size is some multiple
2976	* of the physical sector size.
2977	*
2978	* We'll just truncate the bio to the size of the device,
2979	* and clear the end of the buffer head manually.
2980	*
2981	* Truly out-of-range accesses will turn into actual IO
2982	* errors, this only handles the "we need to be able to
2983	* do IO at the final sector" case.
2984	*/
2985	void guard_bio_eod(int op, struct bio *bio)
2986	{
2987	sector_t maxsector;
2988	struct bio_vec *bvec = bio_last_bvec_all(bio);
2989	unsigned truncated_bytes;
2990	struct hd_struct *part;
2991
2992	rcu_read_lock();
2993	part = __disk_get_part(bio->bi_disk, bio->bi_partno);
2994	if (part)
2995	maxsector = part_nr_sects_read(part);
2996	else
2997	maxsector = get_capacity(bio->bi_disk);
2998	rcu_read_unlock();
2999
3000	if (!maxsector)
3001	return;
3002
3003	/*
3004	* If the whole IO is past the end of the device,
3005	* let it through, and the IO layer will turn it into
3006	* an EIO.
3007	*/
3008	if (unlikely(bio->bi_iter.bi_sector >= maxsector))
3009	return;
3010
3011	maxsector -= bio->bi_iter.bi_sector;
3012	if (likely((bio->bi_iter.bi_size >> 9) <= maxsector))
3013	return;
3014
3015	/* Uhhuh. We've got a bio that straddles the device size! */
3016	truncated_bytes = bio->bi_iter.bi_size - (maxsector << 9);
3017
3018	/* Truncate the bio.. */
3019	bio->bi_iter.bi_size -= truncated_bytes;
3020	bvec->bv_len -= truncated_bytes;
3021
3022	/* ..and clear the end of the buffer for reads */
3023	if (op == REQ_OP_READ) {
3024	zero_user(bvec->bv_page, bvec->bv_offset + bvec->bv_len,
3025	truncated_bytes);
3026	}
3027	}
3028
3029	static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
3030	enum rw_hint write_hint, struct writeback_control *wbc)
3031	{
3032	struct bio *bio;
3033
3034	BUG_ON(!buffer_locked(bh));
3035	BUG_ON(!buffer_mapped(bh));
3036	BUG_ON(!bh->b_end_io);
3037	BUG_ON(buffer_delay(bh));
3038	BUG_ON(buffer_unwritten(bh));
3039
3040	/*
3041	* Only clear out a write error when rewriting
3042	*/
3043	if (test_set_buffer_req(bh) && (op == REQ_OP_WRITE))
3044	clear_buffer_write_io_error(bh);
3045
3046	/*
3047	* from here on down, it's all bio -- do the initial mapping,
3048	* submit_bio -> generic_make_request may further map this bio around
3049	*/
3050	bio = bio_alloc(GFP_NOIO, 1);
3051
3052	if (wbc) {
3053	wbc_init_bio(wbc, bio);
3054	wbc_account_io(wbc, bh->b_page, bh->b_size);
3055	}
3056
3057	bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
3058	bio_set_dev(bio, bh->b_bdev);
3059	bio->bi_write_hint = write_hint;
3060
3061	bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh));
3062	BUG_ON(bio->bi_iter.bi_size != bh->b_size);
3063
3064	bio->bi_end_io = end_bio_bh_io_sync;
3065	bio->bi_private = bh;
3066
3067	/* Take care of bh's that straddle the end of the device */
3068	guard_bio_eod(op, bio);
3069
3070	if (buffer_meta(bh))
3071	op_flags \|= REQ_META;
3072	if (buffer_prio(bh))
3073	op_flags \|= REQ_PRIO;
3074	bio_set_op_attrs(bio, op, op_flags);
3075
3076	submit_bio(bio);
3077	return 0;
3078	}
3079
3080	int submit_bh(int op, int op_flags, struct buffer_head *bh)
3081	{
3082	return submit_bh_wbc(op, op_flags, bh, 0, NULL);
3083	}
3084	EXPORT_SYMBOL(submit_bh);
3085
3086	/**
3087	* ll_rw_block: low-level access to block devices (DEPRECATED)
3088	* @op: whether to %READ or %WRITE
3089	* @op_flags: req_flag_bits
3090	* @nr: number of &struct buffer_heads in the array
3091	* @bhs: array of pointers to &struct buffer_head
3092	*
3093	* ll_rw_block() takes an array of pointers to &struct buffer_heads, and
3094	* requests an I/O operation on them, either a %REQ_OP_READ or a %REQ_OP_WRITE.
3095	* @op_flags contains flags modifying the detailed I/O behavior, most notably
3096	* %REQ_RAHEAD.
3097	*
3098	* This function drops any buffer that it cannot get a lock on (with the
3099	* BH_Lock state bit), any buffer that appears to be clean when doing a write
3100	* request, and any buffer that appears to be up-to-date when doing read
3101	* request. Further it marks as clean buffers that are processed for
3102	* writing (the buffer cache won't assume that they are actually clean
3103	* until the buffer gets unlocked).
3104	*
3105	* ll_rw_block sets b_end_io to simple completion handler that marks
3106	* the buffer up-to-date (if appropriate), unlocks the buffer and wakes
3107	* any waiters.
3108	*
3109	* All of the buffers must be for the same device, and must also be a
3110	* multiple of the current approved size for the device.
3111	*/
3112	void ll_rw_block(int op, int op_flags, int nr, struct buffer_head *bhs[])
3113	{
3114	int i;
3115
3116	for (i = 0; i < nr; i++) {
3117	struct buffer_head *bh = bhs[i];
3118
3119	if (!trylock_buffer(bh))
3120	continue;
3121	if (op == WRITE) {
3122	if (test_clear_buffer_dirty(bh)) {
3123	bh->b_end_io = end_buffer_write_sync;
3124	get_bh(bh);
3125	submit_bh(op, op_flags, bh);
3126	continue;
3127	}
3128	} else {
3129	if (!buffer_uptodate(bh)) {
3130	bh->b_end_io = end_buffer_read_sync;
3131	get_bh(bh);
3132	submit_bh(op, op_flags, bh);
3133	continue;
3134	}
3135	}
3136	unlock_buffer(bh);
3137	}
3138	}
3139	EXPORT_SYMBOL(ll_rw_block);
3140
3141	void write_dirty_buffer(struct buffer_head *bh, int op_flags)
3142	{
3143	lock_buffer(bh);
3144	if (!test_clear_buffer_dirty(bh)) {
3145	unlock_buffer(bh);
3146	return;
3147	}
3148	bh->b_end_io = end_buffer_write_sync;
3149	get_bh(bh);
3150	submit_bh(REQ_OP_WRITE, op_flags, bh);
3151	}
3152	EXPORT_SYMBOL(write_dirty_buffer);
3153
3154	/*
3155	* For a data-integrity writeout, we need to wait upon any in-progress I/O
3156	* and then start new I/O and then wait upon it. The caller must have a ref on
3157	* the buffer_head.
3158	*/
3159	int __sync_dirty_buffer(struct buffer_head *bh, int op_flags)
3160	{
3161	int ret = 0;
3162
3163	WARN_ON(atomic_read(&bh->b_count) < 1);
3164	lock_buffer(bh);
3165	if (test_clear_buffer_dirty(bh)) {
3166	get_bh(bh);
3167	bh->b_end_io = end_buffer_write_sync;
3168	ret = submit_bh(REQ_OP_WRITE, op_flags, bh);
3169	wait_on_buffer(bh);
3170	if (!ret && !buffer_uptodate(bh))
3171	ret = -EIO;
3172	} else {
3173	unlock_buffer(bh);
3174	}
3175	return ret;
3176	}
3177	EXPORT_SYMBOL(__sync_dirty_buffer);
3178
3179	int sync_dirty_buffer(struct buffer_head *bh)
3180	{
3181	return __sync_dirty_buffer(bh, REQ_SYNC);
3182	}
3183	EXPORT_SYMBOL(sync_dirty_buffer);
3184
3185	/*
3186	* try_to_free_buffers() checks if all the buffers on this particular page
3187	* are unused, and releases them if so.
3188	*
3189	* Exclusion against try_to_free_buffers may be obtained by either
3190	* locking the page or by holding its mapping's private_lock.
3191	*
3192	* If the page is dirty but all the buffers are clean then we need to
3193	* be sure to mark the page clean as well. This is because the page
3194	* may be against a block device, and a later reattachment of buffers
3195	* to a dirty page will set all buffers dirty. Which would corrupt
3196	* filesystem data on the same device.
3197	*
3198	* The same applies to regular filesystem pages: if all the buffers are
3199	* clean then we set the page clean and proceed. To do that, we require
3200	* total exclusion from __set_page_dirty_buffers(). That is obtained with
3201	* private_lock.
3202	*
3203	* try_to_free_buffers() is non-blocking.
3204	*/
3205	static inline int buffer_busy(struct buffer_head *bh)
3206	{
3207	return atomic_read(&bh->b_count) \|
3208	(bh->b_state & ((1 << BH_Dirty) \| (1 << BH_Lock)));
3209	}
3210
3211	static int
3212	drop_buffers(struct page page, struct buffer_head *buffers_to_free)
3213	{
3214	struct buffer_head *head = page_buffers(page);
3215	struct buffer_head *bh;
3216
3217	bh = head;
3218	do {
3219	if (buffer_busy(bh))
3220	goto failed;
3221	bh = bh->b_this_page;
3222	} while (bh != head);
3223
3224	do {
3225	struct buffer_head *next = bh->b_this_page;
3226
3227	if (bh->b_assoc_map)
3228	__remove_assoc_queue(bh);
3229	bh = next;
3230	} while (bh != head);
3231	*buffers_to_free = head;
3232	__clear_page_buffers(page);
3233	return 1;
3234	failed:
3235	return 0;
3236	}
3237
3238	int try_to_free_buffers(struct page *page)
3239	{
3240	struct address_space * const mapping = page->mapping;
3241	struct buffer_head *buffers_to_free = NULL;
3242	int ret = 0;
3243
3244	BUG_ON(!PageLocked(page));
3245	if (PageWriteback(page))
3246	return 0;
3247
3248	if (mapping == NULL) { /* can this still happen? */
3249	ret = drop_buffers(page, &buffers_to_free);
3250	goto out;
3251	}
3252
3253	spin_lock(&mapping->private_lock);
3254	ret = drop_buffers(page, &buffers_to_free);
3255
3256	/*
3257	* If the filesystem writes its buffers by hand (eg ext3)
3258	* then we can have clean buffers against a dirty page. We
3259	* clean the page here; otherwise the VM will never notice
3260	* that the filesystem did any IO at all.
3261	*
3262	* Also, during truncate, discard_buffer will have marked all
3263	* the page's buffers clean. We discover that here and clean
3264	* the page also.
3265	*
3266	* private_lock must be held over this entire operation in order
3267	* to synchronise against __set_page_dirty_buffers and prevent the
3268	* dirty bit from being lost.
3269	*/
3270	if (ret)
3271	cancel_dirty_page(page);
3272	spin_unlock(&mapping->private_lock);
3273	out:
3274	if (buffers_to_free) {
3275	struct buffer_head *bh = buffers_to_free;
3276
3277	do {
3278	struct buffer_head *next = bh->b_this_page;
3279	free_buffer_head(bh);
3280	bh = next;
3281	} while (bh != buffers_to_free);
3282	}
3283	return ret;
3284	}
3285	EXPORT_SYMBOL(try_to_free_buffers);
3286
3287	/*
3288	* There are no bdflush tunables left. But distributions are
3289	* still running obsolete flush daemons, so we terminate them here.
3290	*
3291	* Use of bdflush() is deprecated and will be removed in a future kernel.
3292	* The `flush-X' kernel threads fully replace bdflush daemons and this call.
3293	*/
3294	SYSCALL_DEFINE2(bdflush, int, func, long, data)
3295	{
3296	static int msg_count;
3297
3298	if (!capable(CAP_SYS_ADMIN))
3299	return -EPERM;
3300
3301	if (msg_count < 5) {
3302	msg_count++;
3303	printk(KERN_INFO
3304	"warning: process `%s' used the obsolete bdflush"
3305	" system call\n", current->comm);
3306	printk(KERN_INFO "Fix your initscripts?\n");
3307	}
3308
3309	if (func == 1)
3310	do_exit(0);
3311	return 0;
3312	}
3313
3314	/*
3315	* Buffer-head allocation
3316	*/
3317	static struct kmem_cache *bh_cachep __read_mostly;
3318
3319	/*
3320	* Once the number of bh's in the machine exceeds this level, we start
3321	* stripping them in writeback.
3322	*/
3323	static unsigned long max_buffer_heads;
3324
3325	int buffer_heads_over_limit;
3326
3327	struct bh_accounting {
3328	int nr; /* Number of live bh's */
3329	int ratelimit; /* Limit cacheline bouncing */
3330	};
3331
3332	static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3333
3334	static void recalc_bh_state(void)
3335	{
3336	int i;
3337	int tot = 0;
3338
3339	if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
3340	return;
3341	__this_cpu_write(bh_accounting.ratelimit, 0);
3342	for_each_online_cpu(i)
3343	tot += per_cpu(bh_accounting, i).nr;
3344	buffer_heads_over_limit = (tot > max_buffer_heads);
3345	}
3346
3347	struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3348	{
3349	struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
3350	if (ret) {
3351	INIT_LIST_HEAD(&ret->b_assoc_buffers);
3352	preempt_disable();
3353	__this_cpu_inc(bh_accounting.nr);
3354	recalc_bh_state();
3355	preempt_enable();
3356	}
3357	return ret;
3358	}
3359	EXPORT_SYMBOL(alloc_buffer_head);
3360
3361	void free_buffer_head(struct buffer_head *bh)
3362	{
3363	BUG_ON(!list_empty(&bh->b_assoc_buffers));
3364	kmem_cache_free(bh_cachep, bh);
3365	preempt_disable();
3366	__this_cpu_dec(bh_accounting.nr);
3367	recalc_bh_state();
3368	preempt_enable();
3369	}
3370	EXPORT_SYMBOL(free_buffer_head);
3371
3372	static int buffer_exit_cpu_dead(unsigned int cpu)
3373	{
3374	int i;
3375	struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3376
3377	for (i = 0; i < BH_LRU_SIZE; i++) {
3378	brelse(b->bhs[i]);
3379	b->bhs[i] = NULL;
3380	}
3381	this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
3382	per_cpu(bh_accounting, cpu).nr = 0;
3383	return 0;
3384	}
3385
3386	/**
3387	* bh_uptodate_or_lock - Test whether the buffer is uptodate
3388	* @bh: struct buffer_head
3389	*
3390	* Return true if the buffer is up-to-date and false,
3391	* with the buffer locked, if not.
3392	*/
3393	int bh_uptodate_or_lock(struct buffer_head *bh)
3394	{
3395	if (!buffer_uptodate(bh)) {
3396	lock_buffer(bh);
3397	if (!buffer_uptodate(bh))
3398	return 0;
3399	unlock_buffer(bh);
3400	}
3401	return 1;
3402	}
3403	EXPORT_SYMBOL(bh_uptodate_or_lock);
3404
3405	/**
3406	* bh_submit_read - Submit a locked buffer for reading
3407	* @bh: struct buffer_head
3408	*
3409	* Returns zero on success and -EIO on error.
3410	*/
3411	int bh_submit_read(struct buffer_head *bh)
3412	{
3413	BUG_ON(!buffer_locked(bh));
3414
3415	if (buffer_uptodate(bh)) {
3416	unlock_buffer(bh);
3417	return 0;
3418	}
3419
3420	get_bh(bh);
3421	bh->b_end_io = end_buffer_read_sync;
3422	submit_bh(REQ_OP_READ, 0, bh);
3423	wait_on_buffer(bh);
3424	if (buffer_uptodate(bh))
3425	return 0;
3426	return -EIO;
3427	}
3428	EXPORT_SYMBOL(bh_submit_read);
3429
3430	/*
3431	* Seek for SEEK_DATA / SEEK_HOLE within @page, starting at @lastoff.
3432	*
3433	* Returns the offset within the file on success, and -ENOENT otherwise.
3434	*/
3435	static loff_t
3436	page_seek_hole_data(struct page *page, loff_t lastoff, int whence)
3437	{
3438	loff_t offset = page_offset(page);
3439	struct buffer_head bh, head;
3440	bool seek_data = whence == SEEK_DATA;
3441
3442	if (lastoff < offset)
3443	lastoff = offset;
3444
3445	bh = head = page_buffers(page);
3446	do {
3447	offset += bh->b_size;
3448	if (lastoff >= offset)
3449	continue;
3450
3451	/*
3452	* Unwritten extents that have data in the page cache covering
3453	* them can be identified by the BH_Unwritten state flag.
3454	* Pages with multiple buffers might have a mix of holes, data
3455	* and unwritten extents - any buffer with valid data in it
3456	* should have BH_Uptodate flag set on it.
3457	*/
3458
3459	if ((buffer_unwritten(bh) \|\| buffer_uptodate(bh)) == seek_data)
3460	return lastoff;
3461
3462	lastoff = offset;
3463	} while ((bh = bh->b_this_page) != head);
3464	return -ENOENT;
3465	}
3466
3467	/*
3468	* Seek for SEEK_DATA / SEEK_HOLE in the page cache.
3469	*
3470	* Within unwritten extents, the page cache determines which parts are holes
3471	* and which are data: unwritten and uptodate buffer heads count as data;
3472	* everything else counts as a hole.
3473	*
3474	* Returns the resulting offset on successs, and -ENOENT otherwise.
3475	*/
3476	loff_t
3477	page_cache_seek_hole_data(struct inode *inode, loff_t offset, loff_t length,
3478	int whence)
3479	{
3480	pgoff_t index = offset >> PAGE_SHIFT;
3481	pgoff_t end = DIV_ROUND_UP(offset + length, PAGE_SIZE);
3482	loff_t lastoff = offset;
3483	struct pagevec pvec;
3484
3485	if (length <= 0)
3486	return -ENOENT;
3487
3488	pagevec_init(&pvec);
3489
3490	do {
3491	unsigned nr_pages, i;
3492
3493	nr_pages = pagevec_lookup_range(&pvec, inode->i_mapping, &index,
3494	end - 1);
3495	if (nr_pages == 0)
3496	break;
3497
3498	for (i = 0; i < nr_pages; i++) {
3499	struct page *page = pvec.pages[i];
3500
3501	/*
3502	* At this point, the page may be truncated or
3503	* invalidated (changing page->mapping to NULL), or
3504	* even swizzled back from swapper_space to tmpfs file
3505	* mapping. However, page->index will not change
3506	* because we have a reference on the page.
3507	*
3508	* If current page offset is beyond where we've ended,
3509	* we've found a hole.
3510	*/
3511	if (whence == SEEK_HOLE &&
3512	lastoff < page_offset(page))
3513	goto check_range;
3514
3515	lock_page(page);
3516	if (likely(page->mapping == inode->i_mapping) &&
3517	page_has_buffers(page)) {
3518	lastoff = page_seek_hole_data(page, lastoff, whence);
3519	if (lastoff >= 0) {
3520	unlock_page(page);
3521	goto check_range;
3522	}
3523	}
3524	unlock_page(page);
3525	lastoff = page_offset(page) + PAGE_SIZE;
3526	}
3527	pagevec_release(&pvec);
3528	} while (index < end);
3529
3530	/* When no page at lastoff and we are not done, we found a hole. */
3531	if (whence != SEEK_HOLE)
3532	goto not_found;
3533
3534	check_range:
3535	if (lastoff < offset + length)
3536	goto out;
3537	not_found:
3538	lastoff = -ENOENT;
3539	out:
3540	pagevec_release(&pvec);
3541	return lastoff;
3542	}
3543
3544	void __init buffer_init(void)
3545	{
3546	unsigned long nrpages;
3547	int ret;
3548
3549	bh_cachep = kmem_cache_create("buffer_head",
3550	sizeof(struct buffer_head), 0,
3551	(SLAB_RECLAIM_ACCOUNT\|SLAB_PANIC\|
3552	SLAB_MEM_SPREAD),
3553	NULL);
3554
3555	/*
3556	* Limit the bh occupancy to 10% of ZONE_NORMAL
3557	*/
3558	nrpages = (nr_free_buffer_pages() * 10) / 100;
3559	max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3560	ret = cpuhp_setup_state_nocalls(CPUHP_FS_BUFF_DEAD, "fs/buffer:dead",
3561	NULL, buffer_exit_cpu_dead);
3562	WARN_ON(ret < 0);
3563	}