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Groups > linux.kernel > #1313540
| From | Christoph Lameter <cl@linux.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! |
| Date | 2016-01-20 23:00 +0100 |
| Message-ID | <qT8Xg-3WS-13@gated-at.bofh.it> (permalink) |
| References | (3 earlier) <qT2Ia-8li-19@gated-at.bofh.it> <qT2RP-8pt-1@gated-at.bofh.it> <qT3kS-aT-15@gated-at.bofh.it> <qT3kU-aT-57@gated-at.bofh.it> <qT8ue-3LS-11@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
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.
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Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Michal Hocko <mhocko@kernel.org> - 2016-01-20 15:40 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Sasha Levin <sasha.levin@oracle.com> - 2016-01-20 16:00 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Michal Hocko <mhocko@kernel.org> - 2016-01-20 16:20 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Christoph Lameter <cl@linux.com> - 2016-01-20 16:30 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Sasha Levin <sasha.levin@oracle.com> - 2016-01-20 17:00 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Christoph Lameter <cl@linux.com> - 2016-01-20 17:00 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Michal Hocko <mhocko@kernel.org> - 2016-01-20 22:30 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Christoph Lameter <cl@linux.com> - 2016-01-20 23:00 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Michal Hocko <mhocko@kernel.org> - 2016-01-21 09:30 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Christoph Lameter <cl@linux.com> - 2016-01-21 16:50 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Michal Hocko <mhocko@kernel.org> - 2016-01-21 18:00 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Christoph Lameter <cl@linux.com> - 2016-01-21 18:40 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Shiraz Hashim <shiraz.linux.kernel@gmail.com> - 2016-01-22 12:10 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Michal Hocko <mhocko@kernel.org> - 2016-01-22 15:10 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Christoph Lameter <cl@linux.com> - 2016-01-22 17:10 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Michal Hocko <mhocko@kernel.org> - 2016-01-22 17:20 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Christoph Lameter <cl@linux.com> - 2016-01-22 17:50 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Michal Hocko <mhocko@kernel.org> - 2016-01-22 18:20 +0100
fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-01-23 17:30 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Christoph Lameter <cl@linux.com> - 2016-01-24 01:40 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-01-24 03:50 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Christoph Lameter <cl@linux.com> - 2016-01-24 04:50 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-01-24 06:40 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Michal Hocko <mhocko@kernel.org> - 2016-01-25 18:50 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Christoph Lameter <cl@linux.com> - 2016-01-25 19:10 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Michal Hocko <mhocko@kernel.org> - 2016-01-25 21:20 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Christoph Lameter <cl@linux.com> - 2016-01-26 17:30 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Christoph Lameter <cl@linux.com> - 2016-01-26 19:40 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-01-26 19:50 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Christoph Lameter <cl@linux.com> - 2016-01-26 20:30 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-01-27 04:20 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-01-27 05:20 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Christoph Lameter <cl@linux.com> - 2016-01-27 17:30 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-01-26 19:40 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-01-26 03:20 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-01-26 03:30 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Christoph Lameter <cl@linux.com> - 2016-01-26 17:30 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-01-26 18:40 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Christoph Lameter <cl@linux.com> - 2016-01-26 19:20 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Christoph Lameter <cl@linux.com> - 2016-01-26 17:30 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-01-26 18:10 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Christoph Lameter <cl@linux.com> - 2016-01-26 19:30 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-01-26 20:10 +0100
Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle) Christoph Lameter <cl@linux.com> - 2016-01-26 20:30 +0100
[PATCH] mm, vmstat: make quiet_vmstat lighter (was: Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable) again and shut down on idle) Michal Hocko <mhocko@kernel.org> - 2016-01-27 17:50 +0100
Re: [PATCH] mm, vmstat: make quiet_vmstat lighter (was: Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable) again and shut down on idle) Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-01-27 18:10 +0100
Re: [PATCH] mm, vmstat: make quiet_vmstat lighter (was: Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable) again and shut down on idle) Christoph Lameter <cl@linux.com> - 2016-01-27 19:30 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Linus Torvalds <torvalds@linux-foundation.org> - 2016-01-24 18:00 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Christoph Lameter <cl@linux.com> - 2016-01-20 16:20 +0100
Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Michal Hocko <mhocko@kernel.org> - 2016-01-20 16:30 +0100
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