btrfs: wake up async_delalloc_pages waiters after submit

commit ac98141d140444fe93e26471d3074c603b70e2ca upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 69c6786a9fdf29865c85279a0810ecadb29c8e61..ff3f0638cdb907af56c04cc32a710ff01da00cd2 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1202,11 +1202,6 @@ static noinline void async_cow_submit(struct btrfs_work *work)
        nr_pages = (async_chunk->end - async_chunk->start + PAGE_SIZE) >>
                PAGE_SHIFT;
 
-       /* atomic_sub_return implies a barrier */
-       if (atomic_sub_return(nr_pages, &fs_info->async_delalloc_pages) <
-           5 * SZ_1M)
-               cond_wake_up_nomb(&fs_info->async_submit_wait);
-
        /*
         * ->inode could be NULL if async_chunk_start has failed to compress,
         * in which case we don't have anything to submit, yet we need to
@@ -1215,6 +1210,11 @@ static noinline void async_cow_submit(struct btrfs_work *work)
         */
        if (async_chunk->inode)
                submit_compressed_extents(async_chunk);
+
+       /* atomic_sub_return implies a barrier */
+       if (atomic_sub_return(nr_pages, &fs_info->async_delalloc_pages) <
+           5 * SZ_1M)
+               cond_wake_up_nomb(&fs_info->async_submit_wait);
 }
 
 static noinline void async_cow_free(struct btrfs_work *work)