No feedback on this, and no merge, so resending.
--
fs: improve remount,ro coherency
invalidate sb->s_bdev on remount,ro
Fixes a problem reported by "Jorge Boncompte [DTI2]" <jorge@xxxxxxxx>
who is trying to snapshot a minix filesystem image. Added comments
explain the problem.
Signed-off-by: Nick Piggin <npiggin@xxxxxxx>
---
fs/super.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
Index: linux-2.6/fs/super.c
===================================================================
--- linux-2.6.orig/fs/super.c
+++ linux-2.6/fs/super.c
@@ -637,7 +637,7 @@ retry:
int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
{
int retval;
- int remount_rw;
+ int remount_rw, remount_ro;
#ifdef CONFIG_BLOCK
if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev))
@@ -648,9 +648,12 @@ int do_remount_sb(struct super_block *sb
shrink_dcache_sb(sb);
fsync_super(sb);
+ remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
+ remount_rw = !(flags & MS_RDONLY) && (sb->s_flags & MS_RDONLY);
+
/* If we are remounting RDONLY and current sb is read/write,
make sure there are no rw files opened */
- if ((flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY)) {
+ if (remount_ro) {
if (force)
mark_files_ro(sb);
else if (!fs_may_remount_ro(sb))
@@ -659,7 +662,6 @@ int do_remount_sb(struct super_block *sb
if (retval < 0 && retval != -ENOSYS)
return -EBUSY;
}
- remount_rw = !(flags & MS_RDONLY) && (sb->s_flags & MS_RDONLY);
if (sb->s_op->remount_fs) {
lock_super(sb);
@@ -671,6 +673,14 @@ int do_remount_sb(struct super_block *sb
sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);
if (remount_rw)
DQUOT_ON_REMOUNT(sb);
+ /* Some filesystems modify their metadata via some other path
+ than the bdev buffer cache (eg. use a private mapping, or
+ directories in pagecache, etc). Also file data modifications
+ go via their own mappings. So If we try to mount readonly
+ then copy the filesystem from bdev, we could get stale data,
+ so invalidate it to give a best effort at coherency. */
+ if (remount_ro && sb->s_bdev)
+ invalidate_bdev(sb->s_bdev);
return 0;
}
--
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