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Date: Thu, 4 Sep 2014 12:14:51 -0700 (PDT)
From: Hugh Dickins <hughd@google.com>
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To: Oleg Nesterov <oleg@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>, Rik van Riel <riel@redhat.com>,
        Mel Gorman <mgorman@suse.de>, Kautuk Consul <consul.kautuk@gmail.com>,
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        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.cz>, David Rientjes <rientjes@google.com>,
        Ionut Alexa <ionut.m.alexa@gmail.com>,
        Guillaume Morin <guillaume@morinfr.org>, linux-kernel@vger.kernel.org,
        Kirill Tkhai <tkhai@yandex.ru>
Subject: Re: task_numa_fault() && TASK_DEAD
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On Thu, 4 Sep 2014, Oleg Nesterov wrote:
> On 09/04, Peter Zijlstra wrote:
> > On Wed, Sep 03, 2014 at 06:08:19PM +0200, Oleg Nesterov wrote:
> >
> > > And a stupid (really, I don't understand this code) question:
> > >
> > > 	/* for example, ksmd faulting in a user's mm */
> > > 	if (!p->mm)
> > > 		return;

I don't understand your difficulty with that, I thought the comment
was helpful enough.  Does the original commit comment help?

commit 2832bc19f6668fd00116f61f821105040599ef8b
Author: Hugh Dickins <hughd@google.com>
Date:   Wed Dec 19 17:42:16 2012 -0800

    sched: numa: ksm: fix oops in task_numa_placment()
    
    task_numa_placement() oopsed on NULL p->mm when task_numa_fault() got
    called in the handling of break_ksm() for ksmd.  That might be a
    peculiar case, which perhaps KSM could takes steps to avoid? but it's
    more robust if task_numa_placement() allows for such a possibility.