mm: tiny-shmem nommu fix

4b19de6d · Nick Piggin <[email protected]> · 2008-10-02 14:50:16 -07:00

The previous patch db203d53d474aa068984e409d807628f5841da1b ("mm:
tiny-shmem fix lock ordering: mmap_sem vs i_mutex") to fix the lock
ordering in tiny-shmem breaks shared anonymous and IPC memory on NOMMU
architectures because it was using the expanding truncate to signal ramfs
to allocate a physically contiguous RAM backing the inode (otherwise it is
unusable for "memory mapping" it to userspace).

However do_truncate is what caused the lock ordering error, due to it
taking i_mutex.  In this case, we can actually just call ramfs directly to
allocate memory for the mapping, rather than go via truncate.

Acked-by: David Howells <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
Signed-off-by: Nick Piggin <[email protected]>
Cc: Matt Mackall <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Commit: 4b19de6d1cb07c8bcb6778e771f9cfd5bcfdfd3e
Parents: 6c1b7f68

Changes

3 files changed · +8 −1

File	Status	Add	Del	Content
fs/ramfs/file-nommu.c	modified	+1	−1	View file
include/linux/ramfs.h	modified	+1	−0	View file
mm/tiny-shmem.c	modified	+6	−0	View file

fs/ramfs/file-nommu.c

View file

diff --git a/fs/ramfs/file-nommu.c b/fs/ramfs/file-nommu.c
index 52312ec..5145cb9 100644
--- a/fs/ramfs/file-nommu.c
+++ b/fs/ramfs/file-nommu.c
@@ -58,7 +58,7 @@ const struct inode_operations ramfs_file_inode_operations = {
  * size 0 on the assumption that it's going to be used for an mmap of shared
  * memory
  */
-static int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
+int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
 {
 	struct pagevec lru_pvec;
 	unsigned long npages, xpages, loop, limit;

include/linux/ramfs.h

View file

diff --git a/include/linux/ramfs.h b/include/linux/ramfs.h
index b160fb1..37aaf2b 100644
--- a/include/linux/ramfs.h
+++ b/include/linux/ramfs.h
@@ -6,6 +6,7 @@ extern int ramfs_get_sb(struct file_system_type *fs_type,
 	 int flags, const char *dev_name, void *data, struct vfsmount *mnt);
 
 #ifndef CONFIG_MMU
+extern int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize);
 extern unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
 						   unsigned long addr,
 						   unsigned long len,

mm/tiny-shmem.c

View file

diff --git a/mm/tiny-shmem.c b/mm/tiny-shmem.c
index d17cb6f..8d7a27a 100644
--- a/mm/tiny-shmem.c
+++ b/mm/tiny-shmem.c
@@ -80,6 +80,12 @@ struct file *shmem_file_setup(char *name, loff_t size, unsigned long flags)
 	inode->i_nlink = 0;	/* It is unlinked */
 	init_file(file, shm_mnt, dentry, FMODE_WRITE | FMODE_READ,
 			&ramfs_file_operations);
+
+#ifndef CONFIG_MMU
+	error = ramfs_nommu_expand_for_mapping(inode, size);
+	if (error)
+		goto close_file;
+#endif
 	return file;
 
 close_file: