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

From	Oleg Nesterov <oleg@redhat.com>
Newsgroups	linux.kernel
Subject	Re: can't oom-kill zap the victim's memory?
Date	2015-09-20 15:10 +0200
Message-ID	<qaMxt-IY-19@gated-at.bofh.it> (permalink)
References	<q9LN8-2Wt-13@gated-at.bofh.it> <qarW1-4WN-1@gated-at.bofh.it> <qayNP-6j1-3@gated-at.bofh.it> <qaJge-4nK-9@gated-at.bofh.it>
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On 09/20, Michal Hocko wrote:
>
> On Sat 19-09-15 15:24:02, Linus Torvalds wrote:
> > On Sat, Sep 19, 2015 at 8:03 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> > > +
> > > +static void oom_unmap_func(struct work_struct *work)
> > > +{
> > > +       struct mm_struct *mm = xchg(&oom_unmap_mm, NULL);
> > > +
> > > +       if (!atomic_inc_not_zero(&mm->mm_users))
> > > +               return;
> > > +
> > > +       // If this is not safe we can do use_mm() + unuse_mm()
> > > +       down_read(&mm->mmap_sem);
> >
> > I don't think this is safe.
> >
> > What makes you sure that we might not deadlock on the mmap_sem here?
> > For all we know, the process that is going out of memory is in the
> > middle of a mmap(), and already holds the mmap_sem for writing. No?
> >
> > So at the very least that needs to be a trylock, I think.
>
> Agreed.

Why? See my reply to Linus's email.

Just in case, yes sure the unconditonal down_read() is suboptimal, but
this is minor compared to other problems we need to solve.

> > And I'm not
> > sure zap_page_range() is ok with the mmap_sem only held for reading.
> > Normally our rule is that you can *populate* the page tables
> > concurrently, but you can't tear the down
>
> Actually mmap_sem for reading should be sufficient because we do not
> alter the layout. Both MADV_DONTNEED and MADV_FREE require read mmap_sem
> for example.

Yes, but see the ->vm_flags check in madvise_dontneed().

Oleg.

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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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