From: Filipe Manana <fdmanana@xxxxxxxx>
commit f2cb2f39ccc30fa13d3ac078d461031a63960e5b upstream.
If we do a successful RWF_NOWAIT write we end up locking the snapshot lock
of the inode, through a call to check_can_nocow(), but we never unlock it.
This means the next attempt to create a snapshot on the subvolume will
hang forever.
Trivial reproducer:
$ mkfs.btrfs -f /dev/sdb
$ mount /dev/sdb /mnt
$ touch /mnt/foobar
$ chattr +C /mnt/foobar
$ xfs_io -d -c "pwrite -S 0xab 0 64K" /mnt/foobar
$ xfs_io -d -c "pwrite -N -V 1 -S 0xfe 0 64K" /mnt/foobar
$ btrfs subvolume snapshot -r /mnt /mnt/snap
--> hangs
Fix this by unlocking the snapshot lock if check_can_nocow() returned
success.
Fixes: edf064e7c6fec3 ("btrfs: nowait aio support")
CC: stable@xxxxxxxxxxxxxxx # 4.14+
Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/file.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 719e68ab552c5..484803f8b2290 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1922,6 +1922,8 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
inode_unlock(inode);
return -EAGAIN;
}
+ /* check_can_nocow() locks the snapshot lock on success */
+ btrfs_drew_write_unlock(&root->snapshot_lock);
}
current->backing_dev_info = inode_to_bdi(inode);
--
2.25.1
