From: Josef Bacik <josef@toxicpanda.com>
Date: Wed, 14 Jul 2021 14:47:17 -0400
Subject: btrfs: wake up async_delalloc_pages waiters after submit
Git-commit: ac98141d140444fe93e26471d3074c603b70e2ca
Patch-mainline: v5.15-rc1
References: bsc#1202528

We use the async_delalloc_pages mechanism to make sure that we've
completed our async work before trying to continue our delalloc
flushing.  The reason for this is we need to see any ordered extents
that were created by our delalloc flushing.  However we're waking up
before we do the submit work, which is before we create the ordered
extents.  This is a pretty wide race window where we could potentially
think there are no ordered extents and thus exit shrink_delalloc
prematurely.  Fix this by waking us up after we've done the work to
create ordered extents.

CC: stable@vger.kernel.org # 5.4+
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Acked-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/inode.c |   10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1218,16 +1218,14 @@ static noinline void async_cow_submit(st
 	nr_pages = (async_cow->end - async_cow->start + PAGE_SIZE) >>
 		PAGE_SHIFT;
 
-	/*
-	 * atomic_sub_return implies a barrier for waitqueue_active
-	 */
+	if (async_cow->inode)
+		submit_compressed_extents(async_cow->inode, async_cow);
+
+	/* atomic_sub_return implies a barrier for waitqueue_active */
 	if (atomic_sub_return(nr_pages, &fs_info->async_delalloc_pages) <
 	    5 * SZ_1M &&
 	    waitqueue_active(&fs_info->async_submit_wait))
 		wake_up(&fs_info->async_submit_wait);
-
-	if (async_cow->inode)
-		submit_compressed_extents(async_cow->inode, async_cow);
 }
 
 static noinline void async_cow_free(struct btrfs_work *work)