3.19.8-ckt4 -stable review patch. If anyone has any objections, please let me know.
------------------
From: Omar Sandoval <osandov@xxxxxxxxxxx>
commit 773cd04ec1911abb33cf9538b65f55b76cad5d92 upstream.
Since commit 0723a0473fb4 ("btrfs: allow mounting btrfs subvolumes with
different ro/rw options"), when mounting a subvolume read/write when
another subvolume has previously been mounted read-only, we first do a
remount. However, this should be done with the superblock locked, as per
sync_filesystem():
/*
* We need to be protected against the filesystem going from
* r/o to r/w or vice versa.
*/
WARN_ON(!rwsem_is_locked(&sb->s_umount));
This WARN_ON can easily be hit with:
mkfs.btrfs -f /dev/vdb
mount /dev/vdb /mnt
btrfs subvol create /mnt/vol1
btrfs subvol create /mnt/vol2
umount /mnt
mount -oro,subvol=/vol1 /dev/vdb /mnt
mount -orw,subvol=/vol2 /dev/vdb /mnt2
Fixes: 0723a0473fb4 ("btrfs: allow mounting btrfs subvolumes with different ro/rw options")
Reviewed-by: David Sterba <dsterba@xxxxxxx>
Signed-off-by: Omar Sandoval <osandov@xxxxxxxxxxx>
Signed-off-by: Chris Mason <clm@xxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
---
fs/btrfs/super.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 6f49b28..a25cb5b 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1205,7 +1205,9 @@ static struct dentry *mount_subvol(const char *subvol_name, int flags,
return ERR_CAST(mnt);
}
+ down_write(&mnt->mnt_sb->s_umount);
r = btrfs_remount(mnt->mnt_sb, &flags, NULL);
+ up_write(&mnt->mnt_sb->s_umount);
if (r < 0) {
/* FIXME: release vfsmount mnt ??*/
kfree(newargs);
--
1.9.1
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