linux-kernel - Re: [PATCH 0/4] Signal: Fix hard lockup problem in flush

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Date:   Fri, 22 Mar 2019 12:49:17 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Waiman Long <longman@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        selinux@...r.kernel.org, Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Eric Paris <eparis@...isplace.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [PATCH 0/4] Signal: Fix hard lockup problem in flush_sigqueue()

On 03/22, Matthew Wilcox wrote:
>
> On Thu, Mar 21, 2019 at 05:45:08PM -0400, Waiman Long wrote:
> > It was found that if a process has accumulated sufficient number of
> > pending signals, the exiting of that process may cause its parent to
> > have hard lockup when running on a debug kernel with a slow memory
> > freeing path (like with KASAN enabled).
>
> I appreciate these are "reliable" signals, but why do we accumulate so
> many signals to a task which will never receive them?  Can we detect at
> signal delivery time that the task is going to die and avoid queueing
> them in the first place?

A task can block the signal and accumulate up to RLIMIT_SIGPENDING signals,
then it can exit.

Oleg.