linux-kernel - Re: [PATCH] percpu: Allow to kill tasks doing pcpu_alloc() and waiting for pcpu_balance

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Message-ID: <20180314220909.GE2943022@devbig577.frc2.facebook.com>
Date:   Wed, 14 Mar 2018 15:09:09 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Kirill Tkhai <ktkhai@...tuozzo.com>, cl@...ux.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] percpu: Allow to kill tasks doing pcpu_alloc() and
 waiting for pcpu_balance_workfn()

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.

Thanks.

-- 
tejun