Qiang Huang <h.huangqiang@xxxxxxxxxx> writes:
> This looks applicable to stable-3.4, that fixed a potential livelock in
> memcg. I move the changes from memcontrol.c to oom_kill.c, so this will
> fit stable-3.4.
Thanks, I will queue this patch for the 3.5 kernel as well.
Cheers,
--
Luis
>
> ================
>
> From: David Rientjes <rientjes@xxxxxxxxxx>
>
> commit 465adcf1ea7b2e49b2e0899366624f5532b64012
>
> A memcg may livelock when oom if the process that grabs the hierarchy's
> oom lock is never the first process with PF_EXITING set in the memcg's
> task iteration.
>
> The oom killer, both global and memcg, will defer if it finds an
> eligible process that is in the process of exiting and it is not being
> ptraced. The idea is to allow it to exit without using memory reserves
> before needlessly killing another process.
>
> This normally works fine except in the memcg case with a large number of
> threads attached to the oom memcg. In this case, the memcg oom killer
> only gets called for the process that grabs the hierarchy's oom lock;
> all others end up blocked on the memcg's oom waitqueue. Thus, if the
> process that grabs the hierarchy's oom lock is never the first
> PF_EXITING process in the memcg's task iteration, the oom killer is
> constantly deferred without anything making progress.
>
> The fix is to give PF_EXITING processes access to memory reserves so
> that we've marked them as oom killed without any iteration. This allows
> __mem_cgroup_try_charge() to succeed so that the process may exit. This
> makes the memcg oom killer exemption for TIF_MEMDIE tasks, now
> immediately granted for processes with pending SIGKILLs and those in the
> exit path, to be equivalent to what is done for the global oom killer.
>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxx>
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> [Qiang: backported to 3.4:
> - move the changes from memcontrol.c to oom_kill.c]
> Signed-off-by: Qiang Huang <h.huangqiang@xxxxxxxxxx>
> ---
> mm/oom_kill.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 46bf2ed5..597ecac 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -562,11 +562,11 @@ void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
> struct task_struct *p;
>
> /*
> - * If current has a pending SIGKILL, then automatically select it. The
> - * goal is to allow it to allocate so that it may quickly exit and free
> - * its memory.
> + * If current has a pending SIGKILL or is exiting, then automatically
> + * select it. The goal is to allow it to allocate so that it may
> + * quickly exit and free its memory.
> */
> - if (fatal_signal_pending(current)) {
> + if (fatal_signal_pending(current) || current->flags & PF_EXITING) {
> set_thread_flag(TIF_MEMDIE);
> return;
> }
> -- 1.8.3
>
> --
> To unsubscribe from this list: send the line "unsubscribe stable" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe stable" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html