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From: Andrew Morton <akpm@linux-foundation.org>
To: Tejun Heo <tj@kernel.org>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>,
	cl@linux.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] percpu: Allow to kill tasks doing pcpu_alloc() and waiting for pcpu_balance_workfn()
Date: Wed, 14 Mar 2018 15:22:03 -0700	[thread overview]
Message-ID: <20180314152203.c06fce436d221d34d3e4cf4a@linux-foundation.org> (raw)
In-Reply-To: <20180314220909.GE2943022@devbig577.frc2.facebook.com>

On Wed, 14 Mar 2018 15:09:09 -0700 Tejun Heo <tj@kernel.org> wrote:

> Hello, Andrew.
> 
> On Wed, Mar 14, 2018 at 01:56:31PM -0700, Andrew Morton wrote:
> > It would benefit from a comment explaining why we're doing this (it's
> > for the oom-killer).
> 
> Will add.
> 
> > My memory is weak and our documentation is awful.  What does
> > mutex_lock_killable() actually do and how does it differ from
> > mutex_lock_interruptible()?  Userspace tasks can run pcpu_alloc() and I
> 
> IIRC, killable listens only to SIGKILL.
> 
> > wonder if there's any way in which a userspace-delivered signal can
> > disrupt another userspace task's memory allocation attempt?
> 
> Hmm... maybe.  Just honoring SIGKILL *should* be fine but the alloc
> failure paths might be broken, so there are some risks.  Given that
> the cases where userspace tasks end up allocation percpu memory is
> pretty limited and/or priviledged (like mount, bpf), I don't think the
> risks are high tho.

hm.  spose so.  Maybe.  Are there other ways?  I assume the time is
being spent in pcpu_create_chunk()?  We could drop the mutex while
running that stuff and take the appropriate did-we-race-with-someone
testing after retaking it.  Or similar.

  reply	other threads:[~2018-03-14 22:22 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-14 11:51 [PATCH] percpu: Allow to kill tasks doing pcpu_alloc() and waiting for pcpu_balance_workfn() Kirill Tkhai
2018-03-14 13:55 ` Tejun Heo
2018-03-14 20:56 ` Andrew Morton
2018-03-14 22:09   ` Tejun Heo
2018-03-14 22:22     ` Andrew Morton [this message]
2018-03-15  8:58       ` Kirill Tkhai
2018-03-15 10:48         ` Tetsuo Handa
2018-03-15 10:48           ` Tetsuo Handa
2018-03-15 12:09           ` Kirill Tkhai
2018-03-15 12:09             ` Kirill Tkhai
2018-03-15 14:09             ` Tetsuo Handa
2018-03-15 14:42               ` Kirill Tkhai
2018-03-19 15:13       ` Tejun Heo
2018-03-15 11:58   ` [PATCH] Improve mutex documentation Matthew Wilcox
2018-03-15 11:58     ` Matthew Wilcox
2018-03-15 12:12     ` Kirill Tkhai
2018-03-15 12:12       ` Kirill Tkhai
2018-03-15 13:18       ` Matthew Wilcox
2018-03-15 13:18         ` Matthew Wilcox
2018-03-15 13:23         ` Kirill Tkhai
2018-03-15 13:23           ` Kirill Tkhai
2018-03-16 13:57     ` Peter Zijlstra
2018-03-16 13:57       ` Peter Zijlstra
2018-03-20 11:07     ` [tip:locking/urgent] locking/mutex: Improve documentation tip-bot for Matthew Wilcox
2018-03-19 15:14   ` [PATCH] percpu: Allow to kill tasks doing pcpu_alloc() and waiting for pcpu_balance_workfn() Tejun Heo
2018-03-19 15:32     ` [PATCH v2] mm: " Kirill Tkhai
2018-03-19 16:39       ` Tejun Heo

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