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authorNick Piggin <npiggin@suse.de>2009-12-21 19:28:53 -0500
committerAl Viro <viro@zeniv.linux.org.uk>2010-03-03 13:00:20 -0500
commitd208bbdda991b8808d9c033ce4d31cb1bd87dcfc (patch)
tree8589a1f440a261008addb1ed97b75208eb37a6f1 /fs/super.c
parentec4f860597af41c6b71f4de86d8e86f710bfab54 (diff)
fs: improve remount,ro vs buffercache coherency
Invalidate sb->s_bdev on remount,ro. Fixes a problem reported by Jorge Boncompte who is seeing corruption trying to snapshot a minix filesystem image. Some filesystems modify their metadata via a path other than the bdev buffer cache (eg. they may use a private linear mapping for their metadata, or implement directories in pagecache, etc). Also, file data modifications usually go to the bdev via their own mappings. These updates are not coherent with buffercache IO (eg. via /dev/bdev) and never have been. However there could be a reasonable expectation that after a mount -oremount,ro operation then the buffercache should subsequently be coherent with previous filesystem modifications. So invalidate the bdev mappings on a remount,ro operation to provide a coherency point. The problem was exposed when we switched the old rd to brd because old rd didn't really function like a normal block device and updates to rd via mappings other than the buffercache would still end up going into its buffercache. But the same problem has always affected other "normal" block devices, including loop. [akpm@linux-foundation.org: repair comment layout] Reported-by: "Jorge Boncompte [DTI2]" <jorge@dti2.net> Tested-by: "Jorge Boncompte [DTI2]" <jorge@dti2.net> Signed-off-by: Nick Piggin <npiggin@suse.de> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/super.c')
-rw-r--r--fs/super.c18
1 files changed, 15 insertions, 3 deletions
diff --git a/fs/super.c b/fs/super.c
index aff046b0fe7..903896ec7c7 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -568,7 +568,7 @@ out:
568int do_remount_sb(struct super_block *sb, int flags, void *data, int force) 568int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
569{ 569{
570 int retval; 570 int retval;
571 int remount_rw; 571 int remount_rw, remount_ro;
572 572
573 if (sb->s_frozen != SB_UNFROZEN) 573 if (sb->s_frozen != SB_UNFROZEN)
574 return -EBUSY; 574 return -EBUSY;
@@ -583,9 +583,12 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
583 shrink_dcache_sb(sb); 583 shrink_dcache_sb(sb);
584 sync_filesystem(sb); 584 sync_filesystem(sb);
585 585
586 remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
587 remount_rw = !(flags & MS_RDONLY) && (sb->s_flags & MS_RDONLY);
588
586 /* If we are remounting RDONLY and current sb is read/write, 589 /* If we are remounting RDONLY and current sb is read/write,
587 make sure there are no rw files opened */ 590 make sure there are no rw files opened */
588 if ((flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY)) { 591 if (remount_ro) {
589 if (force) 592 if (force)
590 mark_files_ro(sb); 593 mark_files_ro(sb);
591 else if (!fs_may_remount_ro(sb)) 594 else if (!fs_may_remount_ro(sb))
@@ -594,7 +597,6 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
594 if (retval < 0 && retval != -ENOSYS) 597 if (retval < 0 && retval != -ENOSYS)
595 return -EBUSY; 598 return -EBUSY;
596 } 599 }
597 remount_rw = !(flags & MS_RDONLY) && (sb->s_flags & MS_RDONLY);
598 600
599 if (sb->s_op->remount_fs) { 601 if (sb->s_op->remount_fs) {
600 retval = sb->s_op->remount_fs(sb, &flags, data); 602 retval = sb->s_op->remount_fs(sb, &flags, data);
@@ -604,6 +606,16 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
604 sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK); 606 sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);
605 if (remount_rw) 607 if (remount_rw)
606 vfs_dq_quota_on_remount(sb); 608 vfs_dq_quota_on_remount(sb);
609 /*
610 * Some filesystems modify their metadata via some other path than the
611 * bdev buffer cache (eg. use a private mapping, or directories in
612 * pagecache, etc). Also file data modifications go via their own
613 * mappings. So If we try to mount readonly then copy the filesystem
614 * from bdev, we could get stale data, so invalidate it to give a best
615 * effort at coherency.
616 */
617 if (remount_ro && sb->s_bdev)
618 invalidate_bdev(sb->s_bdev);
607 return 0; 619 return 0;
608} 620}
609 621