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memcg, oom: lock mem_cgroup_print_oom_info

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mem_cgroup_print_oom_info uses a static buffer (memcg_name) to store the
name of the cgroup.  This is not safe as pointed out by David Rientjes
because memcg oom is locked only for its hierarchy and nothing prevents
another parallel hierarchy to trigger oom as well and overwrite the
already in-use buffer.

This patch introduces oom_info_lock hidden inside
mem_cgroup_print_oom_info which is held throughout the function.  It
makes access to memcg_name safe and as a bonus it also prevents parallel
memcg ooms to interleave their statistics which would make the printed
data hard to analyze otherwise.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: David Rientjes <rientjes@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:
Michal Hocko 2014-01-21 15:51:04 -08:00 committed by Linus Torvalds
parent 286549dcaf
commit 947b3dd1a8
1 changed files with 7 additions and 5 deletions
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12
mm/memcontrol.c
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@ -1647,13 +1647,13 @@ static void move_unlock_mem_cgroup(struct mem_cgroup *memcg,
*/
void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
{
/*
* protects memcg_name and makes sure that parallel ooms do not
* interleave
*/
static DEFINE_SPINLOCK(oom_info_lock);
struct cgroup *task_cgrp;
struct cgroup *mem_cgrp;
/*
* Need a buffer in BSS, can't rely on allocations. The code relies
* on the assumption that OOM is serialized for memory controller.
* If this assumption is broken, revisit this code.
*/
static char memcg_name[PATH_MAX];
int ret;
struct mem_cgroup *iter;
@ -1662,6 +1662,7 @@ void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
if (!p)
return;
spin_lock(&oom_info_lock);
rcu_read_lock();
mem_cgrp = memcg->css.cgroup;
@ -1730,6 +1731,7 @@ void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
pr_cont("\n");
}
spin_unlock(&oom_info_lock);
}
/*