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memcg: css_put after remove_list

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mem_cgroup_uncharge_page does css_put on the mem_cgroup before uncharging from
it, and before removing page_cgroup from one of its lru lists: isn't there a
danger that struct mem_cgroup memory could be freed and reused before
completing that, so corrupting something?  Never seen it, and for all I know
there may be other constraints which make it impossible; but let's be
defensive and reverse the ordering there.

mem_cgroup_force_empty_list is safe because there's an extra css_get around
all its works; but even so, change its ordering the same way round, to help
get in the habit of doing it like this.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hirokazu Takahashi <taka@valinux.co.jp>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2008-03-04 14:29:12 -08:00 committed by Linus Torvalds
parent b9c565d5a2
commit 6d48ff8bcf
1 changed files with 6 additions and 6 deletions
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12
mm/memcontrol.c
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@ -665,15 +665,15 @@ void mem_cgroup_uncharge_page(struct page *page)
page_assign_page_cgroup(page, NULL);
unlock_page_cgroup(page);
mem = pc->mem_cgroup;
css_put(&mem->css);
res_counter_uncharge(&mem->res, PAGE_SIZE);
mz = page_cgroup_zoneinfo(pc);
spin_lock_irqsave(&mz->lru_lock, flags);
__mem_cgroup_remove_list(pc);
spin_unlock_irqrestore(&mz->lru_lock, flags);
mem = pc->mem_cgroup;
res_counter_uncharge(&mem->res, PAGE_SIZE);
css_put(&mem->css);
kfree(pc);
return;
}
@ -774,9 +774,9 @@ retry:
if (page_get_page_cgroup(page) == pc) {
page_assign_page_cgroup(page, NULL);
unlock_page_cgroup(page);
css_put(&mem->css);
res_counter_uncharge(&mem->res, PAGE_SIZE);
__mem_cgroup_remove_list(pc);
res_counter_uncharge(&mem->res, PAGE_SIZE);
css_put(&mem->css);
kfree(pc);
} else {
/* racing uncharge: let page go then retry */