On Wed 14-12-11 18:39:40, David Rientjes wrote:
> oom, memcg: fix exclusion of memcg threads after they have detached their mm
>
> The oom killer relies on logic that identifies threads that have already
> been oom killed when scanning the tasklist and, if found, deferring until
> such threads have exited. This is done by checking for any candidate
> threads that have the TIF_MEMDIE bit set.
>
> For memcg ooms, candidate threads are first found by calling
> task_in_mem_cgroup() since the oom killer should not defer if there's an
> oom killed thread in another memcg.
>
> Unfortunately, task_in_mem_cgroup() excludes threads if they have
> detached their mm in the process of exiting so TIF_MEMDIE is never
> detected for such conditions. This is different for global, mempolicy,
> and cpuset oom conditions where a detached mm is only excluded after
> checking for TIF_MEMDIE and deferring, if necessary, in
> select_bad_process().
>
> The fix is to return true if a task has a detached mm but is still in the
> memcg or its hierarchy that is currently oom. This will allow the oom
> killer to appropriately defer rather than kill unnecessarily or, in the
> worst case, panic the machine if nothing else is available to kill.
>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
> mm/memcontrol.c | 17 +++++++++++++----
> 1 files changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1109,10 +1109,19 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg)
> struct task_struct *p;
>
> p = find_lock_task_mm(task);
> - if (!p)
> - return 0;
> - curr = try_get_mem_cgroup_from_mm(p->mm);
> - task_unlock(p);
> + if (p) {
> + curr = try_get_mem_cgroup_from_mm(p->mm);
> + task_unlock(p);
> + } else {
> + /*
> + * All threads may have already detached their mm's, but the oom
> + * killer still needs to detect if they have already been oom
> + * killed to prevent needlessly killing additional tasks.
> + */
> + curr = mem_cgroup_from_task(task);
> + if (curr)
> + css_get(&curr->css);
Sorry, but I forgot to mention that we need task_lock(task) around
css_get.
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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