From: Filipe Manana fdmanana@suse.com
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@vger.kernel.org # 4.14+ Signed-off-by: Filipe Manana fdmanana@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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);