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@xxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
> 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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