projects/linux·blob assoc-array-fixes · refs

540 lines · 15.7 KiB

1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Functions to sequence PREFLUSH and FUA writes.
4 *
5 * Copyright (C) 2011 Max Planck Institute for Gravitational Physics
6 * Copyright (C) 2011 Tejun Heo <[email protected]>
7 *
8 * REQ_{PREFLUSH|FUA} requests are decomposed to sequences consisted of three
9 * optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request
10 * properties and hardware capability.
11 *
12 * If a request doesn't have data, only REQ_PREFLUSH makes sense, which
13 * indicates a simple flush request. If there is data, REQ_PREFLUSH indicates
14 * that the device cache should be flushed before the data is executed, and
15 * REQ_FUA means that the data must be on non-volatile media on request
16 * completion.
17 *
18 * If the device doesn't have writeback cache, PREFLUSH and FUA don't make any
19 * difference. The requests are either completed immediately if there's no data
20 * or executed as normal requests otherwise.
21 *
22 * If the device has writeback cache and supports FUA, REQ_PREFLUSH is
23 * translated to PREFLUSH but REQ_FUA is passed down directly with DATA.
24 *
25 * If the device has writeback cache and doesn't support FUA, REQ_PREFLUSH
26 * is translated to PREFLUSH and REQ_FUA to POSTFLUSH.
27 *
28 * The actual execution of flush is double buffered. Whenever a request
29 * needs to execute PRE or POSTFLUSH, it queues at
30 * fq->flush_queue[fq->flush_pending_idx]. Once certain criteria are met, a
31 * REQ_OP_FLUSH is issued and the pending_idx is toggled. When the flush
32 * completes, all the requests which were pending are proceeded to the next
33 * step. This allows arbitrary merging of different types of PREFLUSH/FUA
34 * requests.
35 *
36 * Currently, the following conditions are used to determine when to issue
37 * flush.
38 *
39 * C1. At any given time, only one flush shall be in progress. This makes
40 * double buffering sufficient.
41 *
42 * C2. Flush is deferred if any request is executing DATA of its sequence.
43 * This avoids issuing separate POSTFLUSHes for requests which shared
44 * PREFLUSH.
45 *
46 * C3. The second condition is ignored if there is a request which has
47 * waited longer than FLUSH_PENDING_TIMEOUT. This is to avoid
48 * starvation in the unlikely case where there are continuous stream of
49 * FUA (without PREFLUSH) requests.
50 *
51 * For devices which support FUA, it isn't clear whether C2 (and thus C3)
52 * is beneficial.
53 *
54 * Note that a sequenced PREFLUSH/FUA request with DATA is completed twice.
55 * Once while executing DATA and again after the whole sequence is
56 * complete. The first completion updates the contained bio but doesn't
57 * finish it so that the bio submitter is notified only after the whole
58 * sequence is complete. This is implemented by testing RQF_FLUSH_SEQ in
59 * req_bio_endio().
60 *
61 * The above peculiarity requires that each PREFLUSH/FUA request has only one
62 * bio attached to it, which is guaranteed as they aren't allowed to be
63 * merged in the usual way.
64 */
65
66#include <linux/kernel.h>
67#include <linux/module.h>
68#include <linux/bio.h>
69#include <linux/blkdev.h>
70#include <linux/gfp.h>
71#include <linux/part_stat.h>
72
73#include "blk.h"
74#include "blk-mq.h"
75#include "blk-mq-sched.h"
76
77/* PREFLUSH/FUA sequences */
78enum {
79 REQ_FSEQ_PREFLUSH = (1 << 0), /* pre-flushing in progress */
80 REQ_FSEQ_DATA = (1 << 1), /* data write in progress */
81 REQ_FSEQ_POSTFLUSH = (1 << 2), /* post-flushing in progress */
82 REQ_FSEQ_DONE = (1 << 3),
83
84 REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
85 REQ_FSEQ_POSTFLUSH,
86
87 /*
88 * If flush has been pending longer than the following timeout,
89 * it's issued even if flush_data requests are still in flight.
90 */
91 FLUSH_PENDING_TIMEOUT = 5 * HZ,
92};
93
94static void blk_kick_flush(struct request_queue *q,
95 struct blk_flush_queue *fq, blk_opf_t flags);
96
97static inline struct blk_flush_queue *
98blk_get_flush_queue(struct blk_mq_ctx *ctx)
99{
100 return blk_mq_map_queue(REQ_OP_FLUSH, ctx)->fq;
101}
102
103static unsigned int blk_flush_cur_seq(struct request *rq)
104{
105 return 1 << ffz(rq->flush.seq);
106}
107
108static void blk_flush_restore_request(struct request *rq)
109{
110 /*
111 * After flush data completion, @rq->bio is %NULL but we need to
112 * complete the bio again. @rq->biotail is guaranteed to equal the
113 * original @rq->bio. Restore it.
114 */
115 rq->bio = rq->biotail;
116 if (rq->bio)
117 rq->__sector = rq->bio->bi_iter.bi_sector;
118
119 /* make @rq a normal request */
120 rq->rq_flags &= ~RQF_FLUSH_SEQ;
121 rq->end_io = rq->flush.saved_end_io;
122}
123
124static void blk_account_io_flush(struct request *rq)
125{
126 struct block_device *part = rq->q->disk->part0;
127
128 part_stat_lock();
129 part_stat_inc(part, ios[STAT_FLUSH]);
130 part_stat_add(part, nsecs[STAT_FLUSH],
131 blk_time_get_ns() - rq->start_time_ns);
132 part_stat_unlock();
133}
134
135/**
136 * blk_flush_complete_seq - complete flush sequence
137 * @rq: PREFLUSH/FUA request being sequenced
138 * @fq: flush queue
139 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
140 * @error: whether an error occurred
141 *
142 * @rq just completed @seq part of its flush sequence, record the
143 * completion and trigger the next step.
144 *
145 * CONTEXT:
146 * spin_lock_irq(fq->mq_flush_lock)
147 */
148static void blk_flush_complete_seq(struct request *rq,
149 struct blk_flush_queue *fq,
150 unsigned int seq, blk_status_t error)
151{
152 struct request_queue *q = rq->q;
153 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
154 blk_opf_t cmd_flags;
155
156 BUG_ON(rq->flush.seq & seq);
157 rq->flush.seq |= seq;
158 cmd_flags = rq->cmd_flags;
159
160 if (likely(!error))
161 seq = blk_flush_cur_seq(rq);
162 else
163 seq = REQ_FSEQ_DONE;
164
165 switch (seq) {
166 case REQ_FSEQ_PREFLUSH:
167 case REQ_FSEQ_POSTFLUSH:
168 /* queue for flush */
169 if (list_empty(pending))
170 fq->flush_pending_since = jiffies;
171 list_add_tail(&rq->queuelist, pending);
172 break;
173
174 case REQ_FSEQ_DATA:
175 fq->flush_data_in_flight++;
176 spin_lock(&q->requeue_lock);
177 list_move(&rq->queuelist, &q->requeue_list);
178 spin_unlock(&q->requeue_lock);
179 blk_mq_kick_requeue_list(q);
180 break;
181
182 case REQ_FSEQ_DONE:
183 /*
184 * @rq was previously adjusted by blk_insert_flush() for
185 * flush sequencing and may already have gone through the
186 * flush data request completion path. Restore @rq for
187 * normal completion and end it.
188 */
189 list_del_init(&rq->queuelist);
190 blk_flush_restore_request(rq);
191 blk_mq_end_request(rq, error);
192 break;
193
194 default:
195 BUG();
196 }
197
198 blk_kick_flush(q, fq, cmd_flags);
199}
200
201static enum rq_end_io_ret flush_end_io(struct request *flush_rq,
202 blk_status_t error,
203 const struct io_comp_batch *iob)
204{
205 struct request_queue *q = flush_rq->q;
206 struct list_head *running;
207 struct request *rq, *n;
208 unsigned long flags = 0;
209 struct blk_flush_queue *fq = blk_get_flush_queue(flush_rq->mq_ctx);
210
211 /* release the tag's ownership to the req cloned from */
212 spin_lock_irqsave(&fq->mq_flush_lock, flags);
213
214 if (!req_ref_put_and_test(flush_rq)) {
215 fq->rq_status = error;
216 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
217 return RQ_END_IO_NONE;
218 }
219
220 blk_account_io_flush(flush_rq);
221 /*
222 * Flush request has to be marked as IDLE when it is really ended
223 * because its .end_io() is called from timeout code path too for
224 * avoiding use-after-free.
225 */
226 WRITE_ONCE(flush_rq->state, MQ_RQ_IDLE);
227 if (fq->rq_status != BLK_STS_OK) {
228 error = fq->rq_status;
229 fq->rq_status = BLK_STS_OK;
230 }
231
232 if (!q->elevator) {
233 flush_rq->tag = BLK_MQ_NO_TAG;
234 } else {
235 blk_mq_put_driver_tag(flush_rq);
236 flush_rq->internal_tag = BLK_MQ_NO_TAG;
237 }
238
239 running = &fq->flush_queue[fq->flush_running_idx];
240 BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
241
242 /* account completion of the flush request */
243 fq->flush_running_idx ^= 1;
244
245 /* and push the waiting requests to the next stage */
246 list_for_each_entry_safe(rq, n, running, queuelist) {
247 unsigned int seq = blk_flush_cur_seq(rq);
248
249 BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
250 list_del_init(&rq->queuelist);
251 blk_flush_complete_seq(rq, fq, seq, error);
252 }
253
254 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
255 return RQ_END_IO_NONE;
256}
257
258bool is_flush_rq(struct request *rq)
259{
260 return rq->end_io == flush_end_io;
261}
262
263/**
264 * blk_kick_flush - consider issuing flush request
265 * @q: request_queue being kicked
266 * @fq: flush queue
267 * @flags: cmd_flags of the original request
268 *
269 * Flush related states of @q have changed, consider issuing flush request.
270 * Please read the comment at the top of this file for more info.
271 *
272 * CONTEXT:
273 * spin_lock_irq(fq->mq_flush_lock)
274 *
275 */
276static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
277 blk_opf_t flags)
278{
279 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
280 struct request *first_rq =
281 list_first_entry(pending, struct request, queuelist);
282 struct request *flush_rq = fq->flush_rq;
283
284 /* C1 described at the top of this file */
285 if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
286 return;
287
288 /* C2 and C3 */
289 if (fq->flush_data_in_flight &&
290 time_before(jiffies,
291 fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
292 return;
293
294 /*
295 * Issue flush and toggle pending_idx. This makes pending_idx
296 * different from running_idx, which means flush is in flight.
297 */
298 fq->flush_pending_idx ^= 1;
299
300 blk_rq_init(q, flush_rq);
301
302 /*
303 * In case of none scheduler, borrow tag from the first request
304 * since they can't be in flight at the same time. And acquire
305 * the tag's ownership for flush req.
306 *
307 * In case of IO scheduler, flush rq need to borrow scheduler tag
308 * just for cheating put/get driver tag.
309 */
310 flush_rq->mq_ctx = first_rq->mq_ctx;
311 flush_rq->mq_hctx = first_rq->mq_hctx;
312
313 if (!q->elevator)
314 flush_rq->tag = first_rq->tag;
315 else
316 flush_rq->internal_tag = first_rq->internal_tag;
317
318 flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
319 flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK);
320 flush_rq->rq_flags |= RQF_FLUSH_SEQ;
321 flush_rq->end_io = flush_end_io;
322 /*
323 * Order WRITE ->end_io and WRITE rq->ref, and its pair is the one
324 * implied in refcount_inc_not_zero() called from
325 * blk_mq_find_and_get_req(), which orders WRITE/READ flush_rq->ref
326 * and READ flush_rq->end_io
327 */
328 smp_wmb();
329 req_ref_set(flush_rq, 1);
330
331 spin_lock(&q->requeue_lock);
332 list_add_tail(&flush_rq->queuelist, &q->flush_list);
333 spin_unlock(&q->requeue_lock);
334
335 blk_mq_kick_requeue_list(q);
336}
337
338static enum rq_end_io_ret mq_flush_data_end_io(struct request *rq,
339 blk_status_t error,
340 const struct io_comp_batch *iob)
341{
342 struct request_queue *q = rq->q;
343 struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
344 struct blk_mq_ctx *ctx = rq->mq_ctx;
345 unsigned long flags;
346 struct blk_flush_queue *fq = blk_get_flush_queue(ctx);
347
348 if (q->elevator) {
349 WARN_ON(rq->tag < 0);
350 blk_mq_put_driver_tag(rq);
351 }
352
353 /*
354 * After populating an empty queue, kick it to avoid stall. Read
355 * the comment in flush_end_io().
356 */
357 spin_lock_irqsave(&fq->mq_flush_lock, flags);
358 fq->flush_data_in_flight--;
359 /*
360 * May have been corrupted by rq->rq_next reuse, we need to
361 * re-initialize rq->queuelist before reusing it here.
362 */
363 INIT_LIST_HEAD(&rq->queuelist);
364 blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
365 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
366
367 blk_mq_sched_restart(hctx);
368 return RQ_END_IO_NONE;
369}
370
371static void blk_rq_init_flush(struct request *rq)
372{
373 rq->flush.seq = 0;
374 rq->rq_flags |= RQF_FLUSH_SEQ;
375 rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
376 rq->end_io = mq_flush_data_end_io;
377}
378
379/*
380 * Insert a PREFLUSH/FUA request into the flush state machine.
381 * Returns true if the request has been consumed by the flush state machine,
382 * or false if the caller should continue to process it.
383 */
384bool blk_insert_flush(struct request *rq)
385{
386 struct request_queue *q = rq->q;
387 struct blk_flush_queue *fq = blk_get_flush_queue(rq->mq_ctx);
388 bool supports_fua = q->limits.features & BLK_FEAT_FUA;
389 unsigned int policy = 0;
390
391 /* FLUSH/FUA request must never be merged */
392 WARN_ON_ONCE(rq->bio != rq->biotail);
393
394 if (blk_rq_sectors(rq))
395 policy |= REQ_FSEQ_DATA;
396
397 /*
398 * Check which flushes we need to sequence for this operation.
399 */
400 if (blk_queue_write_cache(q)) {
401 if (rq->cmd_flags & REQ_PREFLUSH)
402 policy |= REQ_FSEQ_PREFLUSH;
403 if ((rq->cmd_flags & REQ_FUA) && !supports_fua)
404 policy |= REQ_FSEQ_POSTFLUSH;
405 }
406
407 /*
408 * @policy now records what operations need to be done. Adjust
409 * REQ_PREFLUSH and FUA for the driver.
410 */
411 rq->cmd_flags &= ~REQ_PREFLUSH;
412 if (!supports_fua)
413 rq->cmd_flags &= ~REQ_FUA;
414
415 /*
416 * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
417 * of those flags, we have to set REQ_SYNC to avoid skewing
418 * the request accounting.
419 */
420 rq->cmd_flags |= REQ_SYNC;
421
422 switch (policy) {
423 case 0:
424 /*
425 * An empty flush handed down from a stacking driver may
426 * translate into nothing if the underlying device does not
427 * advertise a write-back cache. In this case, simply
428 * complete the request.
429 */
430 blk_mq_end_request(rq, 0);
431 return true;
432 case REQ_FSEQ_DATA:
433 /*
434 * If there's data, but no flush is necessary, the request can
435 * be processed directly without going through flush machinery.
436 * Queue for normal execution.
437 */
438 return false;
439 case REQ_FSEQ_DATA | REQ_FSEQ_POSTFLUSH:
440 /*
441 * Initialize the flush fields and completion handler to trigger
442 * the post flush, and then just pass the command on.
443 */
444 blk_rq_init_flush(rq);
445 rq->flush.seq |= REQ_FSEQ_PREFLUSH;
446 spin_lock_irq(&fq->mq_flush_lock);
447 fq->flush_data_in_flight++;
448 spin_unlock_irq(&fq->mq_flush_lock);
449 return false;
450 default:
451 /*
452 * Mark the request as part of a flush sequence and submit it
453 * for further processing to the flush state machine.
454 */
455 blk_rq_init_flush(rq);
456 spin_lock_irq(&fq->mq_flush_lock);
457 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
458 spin_unlock_irq(&fq->mq_flush_lock);
459 return true;
460 }
461}
462
463/**
464 * blkdev_issue_flush - queue a flush
465 * @bdev: blockdev to issue flush for
466 *
467 * Description:
468 * Issue a flush for the block device in question.
469 */
470int blkdev_issue_flush(struct block_device *bdev)
471{
472 struct bio bio;
473
474 bio_init(&bio, bdev, NULL, 0, REQ_OP_WRITE | REQ_PREFLUSH);
475 return submit_bio_wait(&bio);
476}
477EXPORT_SYMBOL(blkdev_issue_flush);
478
479struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,
480 gfp_t flags)
481{
482 struct blk_flush_queue *fq;
483 int rq_sz = sizeof(struct request);
484
485 fq = kzalloc_node(sizeof(*fq), flags, node);
486 if (!fq)
487 goto fail;
488
489 spin_lock_init(&fq->mq_flush_lock);
490
491 rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
492 fq->flush_rq = kzalloc_node(rq_sz, flags, node);
493 if (!fq->flush_rq)
494 goto fail_rq;
495
496 INIT_LIST_HEAD(&fq->flush_queue[0]);
497 INIT_LIST_HEAD(&fq->flush_queue[1]);
498
499 return fq;
500
501 fail_rq:
502 kfree(fq);
503 fail:
504 return NULL;
505}
506
507void blk_free_flush_queue(struct blk_flush_queue *fq)
508{
509 /* bio based request queue hasn't flush queue */
510 if (!fq)
511 return;
512
513 kfree(fq->flush_rq);
514 kfree(fq);
515}
516
517/*
518 * Allow driver to set its own lock class to fq->mq_flush_lock for
519 * avoiding lockdep complaint.
520 *
521 * flush_end_io() may be called recursively from some driver, such as
522 * nvme-loop, so lockdep may complain 'possible recursive locking' because
523 * all 'struct blk_flush_queue' instance share same mq_flush_lock lock class
524 * key. We need to assign different lock class for these driver's
525 * fq->mq_flush_lock for avoiding the lockdep warning.
526 *
527 * Use dynamically allocated lock class key for each 'blk_flush_queue'
528 * instance is over-kill, and more worse it introduces horrible boot delay
529 * issue because synchronize_rcu() is implied in lockdep_unregister_key which
530 * is called for each hctx release. SCSI probing may synchronously create and
531 * destroy lots of MQ request_queues for non-existent devices, and some robot
532 * test kernel always enable lockdep option. It is observed that more than half
533 * an hour is taken during SCSI MQ probe with per-fq lock class.
534 */
535void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx,
536 struct lock_class_key *key)
537{
538 lockdep_set_class(&hctx->fq->mq_flush_lock, key);
539}
540EXPORT_SYMBOL_GPL(blk_mq_hctx_set_fq_lock_class);