Re: can't oom-kill zap the victim's memory?

From	Raymond Jennings <shentino@gmail.com>
Newsgroups	linux.kernel
Subject	Re: can't oom-kill zap the victim's memory?
Date	2015-09-20 21:10 +0200
Message-ID	<qaS9R-i7-33@gated-at.bofh.it> (permalink)
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On 09/20/15 11:05, Linus Torvalds wrote:
> On Sun, Sep 20, 2015 at 5:56 AM, Oleg Nesterov <oleg@redhat.com> wrote:
>> In this case the workqueue thread will block.
> What workqueue thread?
>
>     pagefault_out_of_memory ->
>        out_of_memory ->
>           oom_kill_process
>
> as far as I can tell, this can be called by any task. Now, that
> pagefault case should only happen when the page fault comes from user
> space, but we also have
>
>     __alloc_pages_slowpath ->
>        __alloc_pages_may_oom ->
>           out_of_memory ->
>              oom_kill_process
>
> which can be called from just about any context (but atomic
> allocations will never get here, so it can schedule etc).

I think in this case the oom killer should just slap a SIGKILL on the 
task and then back out, and whatever needed the memory should just wait 
patiently for the sacrificial lamb to commit seppuku.

Which, btw, we should IMO encourage ASAP in the context of the lamb by 
having anything potentially locky or semaphory pay attention to if the 
task in question has a fatal signal pending, and if so, drop everything 
and run like hell so that the task can cough up any locks or semaphores.
> So what's your point? Explain again just how do you guarantee that you
> can take the mmap_sem.
>
>                         Linus
>
> --
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Also, I observed that a task in the middle of dumping core doesn't 
respond to signals while it's dumping, and I would guess that might be 
the case even if the task receives a SIGKILL from the OOM handler.  Just 
a potential observation.

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Thread

[PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Kyle Walker <kwalker@redhat.com> - 2015-09-17 20:10 +0200
  Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Oleg Nesterov <oleg@redhat.com> - 2015-09-17 21:30 +0200
    Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Christoph Lameter <cl@linux.com> - 2015-09-18 17:50 +0200
      Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Oleg Nesterov <oleg@redhat.com> - 2015-09-18 18:30 +0200
        Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2015-09-18 18:50 +0200
          Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Oleg Nesterov <oleg@redhat.com> - 2015-09-18 19:00 +0200
        Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Christoph Lameter <cl@linux.com> - 2015-09-18 19:10 +0200
          Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Oleg Nesterov <oleg@redhat.com> - 2015-09-18 21:20 +0200
            Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Christoph Lameter <cl@linux.com> - 2015-09-18 21:20 +0200
              Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Christoph Lameter <cl@linux.com> - 2015-09-19 00:10 +0200
          Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Michal Hocko <mhocko@kernel.org> - 2015-09-19 10:40 +0200
            Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2015-09-19 16:40 +0200
              Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Michal Hocko <mhocko@kernel.org> - 2015-09-19 18:00 +0200
              Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks David Rientjes <rientjes@google.com> - 2015-09-22 01:40 +0200
                Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2015-09-22 07:40 +0200
            Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Oleg Nesterov <oleg@redhat.com> - 2015-09-19 16:50 +0200
          Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks David Rientjes <rientjes@google.com> - 2015-09-22 01:30 +0200
      Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Michal Hocko <mhocko@kernel.org> - 2015-09-19 10:30 +0200
  Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks Michal Hocko <mhocko@kernel.org> - 2015-09-19 10:30 +0200
    Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks David Rientjes <rientjes@google.com> - 2015-09-22 01:10 +0200
  can't oom-kill zap the victim's memory? Oleg Nesterov <oleg@redhat.com> - 2015-09-19 17:10 +0200
    Re: can't oom-kill zap the victim's memory? Oleg Nesterov <oleg@redhat.com> - 2015-09-19 17:20 +0200
    Re: can't oom-kill zap the victim's memory? Michal Hocko <mhocko@kernel.org> - 2015-09-19 18:00 +0200
      Re: can't oom-kill zap the victim's memory? Oleg Nesterov <oleg@redhat.com> - 2015-09-20 15:20 +0200
    Re: can't oom-kill zap the victim's memory? Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-20 00:30 +0200
      Re: can't oom-kill zap the victim's memory? Raymond Jennings <shentino@gmail.com> - 2015-09-20 01:10 +0200
        Re: can't oom-kill zap the victim's memory? Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-20 01:20 +0200
      Re: can't oom-kill zap the victim's memory? Michal Hocko <mhocko@kernel.org> - 2015-09-20 11:40 +0200
        Re: can't oom-kill zap the victim's memory? Oleg Nesterov <oleg@redhat.com> - 2015-09-20 15:10 +0200
      Re: can't oom-kill zap the victim's memory? Oleg Nesterov <oleg@redhat.com> - 2015-09-20 15:10 +0200
        Re: can't oom-kill zap the victim's memory? Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-20 20:10 +0200
          Re: can't oom-kill zap the victim's memory? Raymond Jennings <shentino@gmail.com> - 2015-09-20 21:10 +0200
            Re: can't oom-kill zap the victim's memory? Oleg Nesterov <oleg@redhat.com> - 2015-09-21 16:10 +0200
          Re: can't oom-kill zap the victim's memory? Oleg Nesterov <oleg@redhat.com> - 2015-09-21 15:50 +0200
            Re: can't oom-kill zap the victim's memory? Michal Hocko <mhocko@kernel.org> - 2015-09-21 16:30 +0200
              Re: can't oom-kill zap the victim's memory? Oleg Nesterov <oleg@redhat.com> - 2015-09-21 17:40 +0200
                Re: can't oom-kill zap the victim's memory? Michal Hocko <mhocko@kernel.org> - 2015-09-21 18:20 +0200
                Re: can't oom-kill zap the victim's memory? Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2015-09-21 19:00 +0200
                Re: can't oom-kill zap the victim's memory? David Rientjes <rientjes@google.com> - 2015-09-22 01:50 +0200
            Re: can't oom-kill zap the victim's memory? Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-21 19:00 +0200
    Re: can't oom-kill zap the victim's memory? Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2015-09-20 17:00 +0200
      Re: can't oom-kill zap the victim's memory? Oleg Nesterov <oleg@redhat.com> - 2015-09-20 17:00 +0200

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