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

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Message-ID: <CA+55aFyajHq2W9HhJWbLASFkTx_kLSHtHuY6mDHKxmoW-LnVEw@mail.gmail.com>
Date:	Sun, 20 Sep 2015 11:05:04 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Kyle Walker <kwalker@...hat.com>, Christoph Lameter <cl@...ux.com>,
	Michal Hocko <mhocko@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Vladimir Davydov <vdavydov@...allels.com>,
	linux-mm <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Stanislav Kozina <skozina@...hat.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Subject: Re: can't oom-kill zap the victim's memory?

On Sun, Sep 20, 2015 at 5:56 AM, Oleg Nesterov <oleg@...hat.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).

So what's your point? Explain again just how do you guarantee that you
can take the mmap_sem.

                       Linus
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