[PATCH] btrfs: don't call destroy_workqueue on NULL workqueues

[Christoph Hellwig <hch@lst.de>]

Unlike the btrfs_workueue code, the kernel workqueues don't like their
cleaup function called on a NULL pointer, so add checks for them.

Fixes: a5eec25648da ("btrfs: use a normal workqueue for rmw_workers")
Reported-by: syzbot+a2c720e0f056114ea7c6@syzkaller.appspotmail.com
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: syzbot+a2c720e0f056114ea7c6@syzkaller.appspotmail.com
---
 fs/btrfs/disk-io.c | 3 ++-
 fs/btrfs/scrub.c   | 9 ++++++---
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 307230436ecd6..fd8d91947d3fc 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2283,7 +2283,8 @@ static void btrfs_stop_all_workers(struct btrfs_fs_info *fs_info)
 	btrfs_destroy_workqueue(fs_info->workers);
 	btrfs_destroy_workqueue(fs_info->endio_workers);
 	btrfs_destroy_workqueue(fs_info->endio_raid56_workers);
-	destroy_workqueue(fs_info->rmw_workers);
+	if (fs_info->rmw_workers)
+		destroy_workqueue(fs_info->rmw_workers);
 	btrfs_destroy_workqueue(fs_info->endio_write_workers);
 	btrfs_destroy_workqueue(fs_info->endio_freespace_worker);
 	btrfs_destroy_workqueue(fs_info->delayed_workers);
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index a614ddde8c624..3985225f27be5 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -3967,9 +3967,12 @@ static void scrub_workers_put(struct btrfs_fs_info *fs_info)
 		fs_info->scrub_parity_workers = NULL;
 		mutex_unlock(&fs_info->scrub_lock);
 
-		destroy_workqueue(scrub_workers);
-		destroy_workqueue(scrub_wr_comp);
-		destroy_workqueue(scrub_parity);
+		if (scrub_workers)
+			destroy_workqueue(scrub_workers);
+		if (scrub_wr_comp)
+			destroy_workqueue(scrub_wr_comp);
+		if (scrub_parity)
+			destroy_workqueue(scrub_parity);
 	}
 }
 
-- 
2.30.2