cgroup, memcg, writeback: drop spurious rcu locking around mem_cgroup_css_from_page()
In earlier versions, mem_cgroup_css_from_page() could return non-root
css on a legacy hierarchy which can go away and required rcu locking;
however, the eventual version simply returns the root cgroup if memcg is
on a legacy hierarchy and thus doesn't need rcu locking around or in it.
Remove spurious rcu lockings.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 023f6a1..6915c95 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -677,9 +677,7 @@
if (!wbc->wb)
return;
- rcu_read_lock();
id = mem_cgroup_css_from_page(page)->id;
- rcu_read_unlock();
if (id == wbc->wb_id) {
wbc->wb_bytes += bytes;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index bee6b1c..23d8cf5 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -382,14 +382,11 @@
{
struct mem_cgroup *memcg;
- rcu_read_lock();
-
memcg = page->mem_cgroup;
if (!memcg || !cgroup_subsys_on_dfl(memory_cgrp_subsys))
memcg = root_mem_cgroup;
- rcu_read_unlock();
return &memcg->css;
}