Messages in this thread |  | | Date | Wed, 11 Dec 2013 14:23:18 -0800 (PST) | From | David Rientjes <> | Subject | Re: [PATCH] memcg, oom: lock mem_cgroup_print_oom_info |
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On Wed, 11 Dec 2013, Michal Hocko wrote:
> 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 make 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>
Acked-by: David Rientjes <rientjes@google.com>
> --- > mm/memcontrol.c | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 28c9221b74ea..c72b03bf9679 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
Parallel memcg oom kills can happen in disjoint memcg hierarchies, this just prevents the printing of the statistics from interleaving. I'm not sure if that's clear from this comment.
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