[PATCH v2 2/3] writeback: drop now-unnecessary rcu_barrier() in cgroup_writeback_umount()

[Baokun Li]

Commit e1b849cfa6b6 ("writeback: Avoid contention on wb->list_lock when
switching inodes") replaced the queue_rcu_work() based scheduling of
inode wb switches with a plain queue_work().  Since then no switcher
goes through call_rcu(), so rcu_barrier() in cgroup_writeback_umount()
has no work to wait for and is effectively a no-op.

Fixes: e1b849cfa6b6 ("writeback: Avoid contention on wb->list_lock when switching inodes")
Signed-off-by: Baokun Li <libaokun@xxxxxxxxxxxxxxxxx>
---
 fs/fs-writeback.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 1f95ddcee363..9ae290547eb2 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1246,11 +1246,6 @@ void cgroup_writeback_umount(struct super_block *sb)
 		 * will then drain it.
 		 */
 		synchronize_rcu();
-		/*
-		 * Use rcu_barrier() to wait for all pending callbacks to
-		 * ensure that all in-flight wb switches are in the workqueue.
-		 */
-		rcu_barrier();
 		flush_workqueue(isw_wq);
 	}
 }
-- 
2.43.7