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Date:   Fri, 22 Mar 2019 12:49:17 +0100
From:   Oleg Nesterov <oleg@redhat.com>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Waiman Long <longman@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>,
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        Eric Paris <eparis@parisplace.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>
Subject: Re: [PATCH 0/4] Signal: Fix hard lockup problem in flush_sigqueue()
Message-ID: <20190322114917.GC28876@redhat.com>
References: <20190321214512.11524-1-longman@redhat.com>
 <20190322101535.GA10344@bombadil.infradead.org>
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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.