linux-kernel - Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408!

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Message-ID: <20160122140418.GB19465@dhcp22.suse.cz>
Date:	Fri, 22 Jan 2016 15:04:18 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408!

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