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Date: Fri, 22 Jan 2016 15:04:18 +0100
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408!
Message-ID: <20160122140418.GB19465@dhcp22.suse.cz>
References: <20160120151007.GG14187@dhcp22.suse.cz>
 <alpine.DEB.2.20.1601200919520.21490@east.gentwo.org>
 <569FAC90.5030407@oracle.com>
 <alpine.DEB.2.20.1601200954420.23983@east.gentwo.org>
 <20160120212806.GA26965@dhcp22.suse.cz>
 <alpine.DEB.2.20.1601201552590.26496@east.gentwo.org>
 <20160121082402.GA29520@dhcp22.suse.cz>
 <alpine.DEB.2.20.1601210941540.7063@east.gentwo.org>
 <20160121165148.GF29520@dhcp22.suse.cz>
 <alpine.DEB.2.20.1601211130580.7741@east.gentwo.org>
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Sender: owner-linux-mm@kvack.org
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To: Christoph Lameter <cl@linux.com>
Cc: Sasha Levin <sasha.levin@oracle.com>, LKML <linux-kernel@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>

On Thu 21-01-16 11:38:46, Christoph Lameter wrote:
> On Thu, 21 Jan 2016, Michal Hocko wrote:
> 
> > It goes like this:
> > CPU0:						CPU1
> > vmstat_update
> >   cpumask_test_and_set_cpu (0->1)
> > [...]
> > 						vmstat_shepherd
> > <enter idle>					  cpumask_test_and_clear_cpu(CPU0) (1->0)
> > quiet_vmstat
> >   cpumask_test_and_set_cpu (0->1)
> >   						  queue_delayed_work_on(CPU0)
> > refresh_cpu_vm_stats()
> > [...]
> > vmstat_update
> >   nothing_to_do
> >   cpumask_test_and_set_cpu (1->1)
> >   VM_BUG_ON
> >
> > Or am I missing something?
> 
> Ok then the following should fix it:

Wouldn't it be much more easier and simply get rid of the VM_BUG_ON?
What is the point of keeping it in the first place. The code can
perfectly cope with the race.
-- 
Michal Hocko
SUSE Labs

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