From 947b3dd1a84ba3fcb7163688fdc36671941786f4 Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Tue, 21 Jan 2014 15:51:04 -0800 Subject: memcg, oom: lock mem_cgroup_print_oom_info 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 Cc: Johannes Weiner Cc: KOSAKI Motohiro Cc: KAMEZAWA Hiroyuki Acked-by: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memcontrol.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 08541f680d90..57b16083f046 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -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) { - 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. + * 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; 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 @@ done: pr_cont("\n"); } + spin_unlock(&oom_info_lock); } /* -- cgit v1.2.3