[PATCH] mm: memcontrol: remove rcu_read_lock from get_mem_cgroup_from_page
From: Muchun Song <hidden>
Date: 2021-02-05 06:30:16
Also in:
cgroups, lkml
Subsystem:
control group - memory resource controller (memcg), memory management, the rest · Maintainers:
Johannes Weiner, Michal Hocko, Roman Gushchin, Shakeel Butt, Andrew Morton, Linus Torvalds
The get_mem_cgroup_from_page() is called under page lock, so the page memcg cannot be changed under us. Also, css_get is enough because page has a reference to the memcg. If we really want to make the get_mem_cgroup_from_page() suitable for arbitrary page, we should use page_memcg_rcu() instead of page_memcg() and call it after rcu_read_lock(). Signed-off-by: Muchun Song <redacted> --- mm/memcontrol.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 87f01bc05d1f..6c7f1ea3955e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c@@ -1063,16 +1063,15 @@ EXPORT_SYMBOL(get_mem_cgroup_from_mm); */ struct mem_cgroup *get_mem_cgroup_from_page(struct page *page) { - struct mem_cgroup *memcg = page_memcg(page); + struct mem_cgroup *memcg; if (mem_cgroup_disabled()) return NULL; - rcu_read_lock(); /* Page should not get uncharged and freed memcg under us. */ - if (!memcg || WARN_ON_ONCE(!css_tryget(&memcg->css))) - memcg = root_mem_cgroup; - rcu_read_unlock(); + memcg = page_memcg(page) ? : root_mem_cgroup; + css_get(&memcg->css); + return memcg; } EXPORT_SYMBOL(get_mem_cgroup_from_page);
--
2.11.0