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@xxxxxxxxxx>
Reported-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
fs/fs-writeback.c | 2 --
mm/memcontrol.c | 3 ---
2 files changed, 5 deletions(-)
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 @@ void wbc_account_io(struct writeback_control *wbc, struct page *page,
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 fc10620..3230201 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -431,14 +431,11 @@ struct cgroup_subsys_state *mem_cgroup_css_from_page(struct page *page)
{
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;
}
--
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