[PATCH] writeback, cgroup: remove extra percpu_ref_exit()

[Greg Thelen]

5.10 stable commit 2b00b2a0e642 ("writeback, cgroup: fix null-ptr-deref
write in bdi_split_work_to_wbs") is a backport of upstream 6.3 commit
1ba1199ec574.

In the 5.10 stable commit backport percpu_ref_exit() is called twice:
first in cgwb_release_workfn() and then in cgwb_free_rcu(). The 2nd call
is benign as percpu_ref_exit() internally detects there's nothing to do.

This fixes an non-upstream issue that only applies to 5.10.y.

Fixes: 2b00b2a0e642 ("writeback, cgroup: fix null-ptr-deref write in bdi_split_work_to_wbs")
Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx>
---
 mm/backing-dev.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index b28f629c3527..dd08ab928e07 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -404,7 +404,6 @@ static void cgwb_release_workfn(struct work_struct *work)
 	blkcg_unpin_online(blkcg);
 
 	fprop_local_destroy_percpu(&wb->memcg_completions);
-	percpu_ref_exit(&wb->refcnt);
 	wb_exit(wb);
 	call_rcu(&wb->rcu, cgwb_free_rcu);
 }
-- 
2.40.1.698.g37aff9b760-goog