This is a note to let you know that I've just added the patch titled
btrfs: fix hang on snapshot creation after RWF_NOWAIT write
to the 5.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
btrfs-fix-hang-on-snapshot-creation-after-rwf_nowait-write.patch
and it can be found in the queue-5.7 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From f2cb2f39ccc30fa13d3ac078d461031a63960e5b Mon Sep 17 00:00:00 2001
From: Filipe Manana <fdmanana@xxxxxxxx>
Date: Mon, 15 Jun 2020 18:46:01 +0100
Subject: btrfs: fix hang on snapshot creation after RWF_NOWAIT write
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(+)
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1922,6 +1922,8 @@ static ssize_t btrfs_file_write_iter(str
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);
Patches currently in stable-queue which might be from fdmanana@xxxxxxxx are
queue-5.7/btrfs-fix-bytes_may_use-underflow-when-running-balance-and-scrub-in-parallel.patch
queue-5.7/btrfs-fix-rwf_nowait-write-not-failling-when-we-need-to-cow.patch
queue-5.7/btrfs-fix-hang-on-snapshot-creation-after-rwf_nowait-write.patch
queue-5.7/btrfs-fix-failure-of-rwf_nowait-write-into-prealloc-extent-beyond-eof.patch
queue-5.7/btrfs-check-if-a-log-root-exists-before-locking-the-log_mutex-on-unlink.patch
queue-5.7/btrfs-fix-data-block-group-relocation-failure-due-to-concurrent-scrub.patch
queue-5.7/btrfs-fix-a-block-group-ref-counter-leak-after-failu.patch
