From 654a0dd0953fcd87ff7bbb468fb889f0eb67df33 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 15 Jan 2016 16:57:16 -0800 Subject: [PATCH] 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 Reported-by: Johannes Weiner Cc: Michal Hocko Cc: Vladimir Davydov Cc: Jens Axboe Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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 023f6a1f23cd..6915c950e6e8 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 bee6b1c9fdce..23d8cf5a86c3 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -382,14 +382,11 @@ 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; } -- 2.20.1