From: Christoph Lameter <cl@linux.com>
To: Michal Hocko <mhocko@kernel.org>
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>
Subject: Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408!
Date: Wed, 20 Jan 2016 15:57:43 -0600 (CST) [thread overview]
Message-ID: <alpine.DEB.2.20.1601201552590.26496@east.gentwo.org> (raw)
In-Reply-To: <20160120212806.GA26965@dhcp22.suse.cz>
On Wed, 20 Jan 2016, Michal Hocko wrote:
> On Wed 20-01-16 09:55:22, Christoph Lameter wrote:
> [...]
> > Subject: vmstat: Remove BUG_ON from vmstat_update
> >
> > If we detect that there is nothing to do just set the flag and do not check
> > if it was already set before. Races really do not matter. If the flag is
> > set by any code then the shepherd will start dealing with the situation
> > and reenable the vmstat workers when necessary again.
> >
> > Concurrent actions could be onlining and offlining of processors or be a
> > result of concurrency issues when updating the cpumask from multiple
> > processors.
>
> Now that 7e988032 ("vmstat: make vmstat_updater deferrable again and
> shut down on idle) is merged the VM_BUG_ON is simply bogus because
> vmstat_update might "race" with quiet_vmstat. The changelog should
> reflect that. What about the following wording?
How can it race if preemption is off?
> Since 0eb77e988032 ("vmstat: make vmstat_updater deferrable again and
> shut down on idle") quiet_vmstat might update cpu_stat_off and mark a
> particular cpu to be handled by vmstat_shepherd. This might trigger
> a VM_BUG_ON in vmstat_update because the work item might have been
> sleeping during the idle period and see the cpu_stat_off updated after
> the wake up. The VM_BUG_ON is therefore misleading and no more
> appropriate. Moreover it doesn't really suite any protection from real
> bugs because vmstat_shepherd will simply reschedule the vmstat_work
> anytime it sees a particular cpu set or vmstat_update would do the same
> from the worker context directly. Even when the two would race the
> result wouldn't be incorrect as the counters update is fully idempotent.
Hmmm... the vmstat_update can be interrupted while running and the cpu put
into idle mode? If vmstat_update is running then the cpu is not idle but
running code. If this is really going on then there is other stuff wrong
with the idling logic.
> Fixes: 0eb77e988032 ("vmstat: make vmstat_updater deferrable again and
> shut down on idle")
> CC: stable # 4.4+
?? There has not been an upstream release with this yet.
next prev parent reply other threads:[~2016-01-20 21:57 UTC|newest]
Thread overview: 77+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-19 0:33 mm, vmstat: kernel BUG at mm/vmstat.c:1408! Sasha Levin
2015-12-21 13:08 ` Christoph Lameter
2015-12-21 20:28 ` Sasha Levin
2015-12-21 21:07 ` Sasha Levin
2015-12-21 21:14 ` Christoph Lameter
2015-12-22 17:21 ` Christoph Lameter
2015-12-24 20:14 ` Sasha Levin
2015-12-29 17:01 ` Christoph Lameter
2015-12-29 17:18 ` Christoph Lameter
2016-01-04 18:05 ` Christoph Lameter
2016-01-04 18:46 ` Sasha Levin
2016-01-12 11:31 ` Shiraz Hashim
2016-01-12 12:23 ` Christoph Lameter
2016-01-12 12:27 ` Shiraz Hashim
2016-01-13 11:36 ` Shiraz Hashim
2016-01-13 12:32 ` Shiraz Hashim
2016-01-14 21:06 ` Sasha Levin
2016-01-20 14:37 ` Michal Hocko
2016-01-20 14:56 ` Sasha Levin
2016-01-20 15:10 ` Michal Hocko
2016-01-20 15:20 ` Christoph Lameter
2016-01-20 15:49 ` Sasha Levin
2016-01-20 15:55 ` Christoph Lameter
2016-01-20 21:28 ` Michal Hocko
2016-01-20 21:57 ` Christoph Lameter [this message]
2016-01-21 8:24 ` Michal Hocko
2016-01-21 15:45 ` Christoph Lameter
2016-01-21 16:51 ` Michal Hocko
2016-01-21 17:38 ` Christoph Lameter
2016-01-22 11:00 ` Shiraz Hashim
2016-01-22 14:04 ` Michal Hocko
2016-01-22 16:07 ` Christoph Lameter
2016-01-22 16:12 ` Michal Hocko
2016-01-22 16:46 ` Christoph Lameter
2016-01-22 17:12 ` Michal Hocko
2016-01-23 16:21 ` fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Mike Galbraith
2016-01-24 0:33 ` Christoph Lameter
2016-01-24 2:46 ` Mike Galbraith
2016-01-24 3:46 ` Christoph Lameter
2016-01-24 5:36 ` Mike Galbraith
2016-01-25 17:42 ` Michal Hocko
2016-01-25 18:02 ` Christoph Lameter
2016-01-25 20:13 ` Michal Hocko
2016-01-26 16:25 ` Christoph Lameter
2016-01-26 18:31 ` Mike Galbraith
2016-01-26 18:34 ` Christoph Lameter
2016-01-26 18:45 ` Mike Galbraith
2016-01-26 19:20 ` Christoph Lameter
2016-01-27 3:12 ` Mike Galbraith
2016-01-27 4:15 ` Mike Galbraith
2016-01-27 16:28 ` Christoph Lameter
2016-01-28 15:36 ` Frederic Weisbecker
2016-01-28 16:42 ` Christoph Lameter
2016-01-26 2:14 ` Mike Galbraith
2016-01-26 2:25 ` Mike Galbraith
2016-01-26 16:26 ` Christoph Lameter
2016-01-26 17:39 ` Mike Galbraith
2016-01-26 18:19 ` Christoph Lameter
2016-01-26 16:26 ` Christoph Lameter
2016-01-26 17:08 ` Mike Galbraith
2016-01-26 18:22 ` Christoph Lameter
2016-01-26 19:09 ` Mike Galbraith
2016-01-26 19:22 ` Christoph Lameter
2016-01-27 16:48 ` [PATCH] mm, vmstat: make quiet_vmstat lighter (was: Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable) " Michal Hocko
2016-01-27 17:03 ` Mike Galbraith
2016-01-27 18:26 ` Christoph Lameter
2016-01-28 15:21 ` Michal Hocko
2016-01-28 16:40 ` Christoph Lameter
2016-01-28 16:53 ` Michal Hocko
2016-01-28 17:05 ` Christoph Lameter
2016-01-28 15:31 ` Michal Hocko
2016-01-28 15:37 ` [PATCH] vmstat: make vmstat_update deferrable (was: Re: [PATCH] mm, vmstat: make quiet_vmstat lighter) " Michal Hocko
2016-01-28 16:48 ` Christoph Lameter
2016-01-28 16:42 ` [PATCH] mm, vmstat: make quiet_vmstat lighter (was: Re: fast " Christoph Lameter
2016-01-24 16:57 ` mm, vmstat: kernel BUG at mm/vmstat.c:1408! Linus Torvalds
2016-01-20 15:14 ` Christoph Lameter
2016-01-20 15:20 ` Michal Hocko
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