linux-kernel - Re: [BUG 2.6.25-rc3] scheduler/hotplug: some processes are dealocked when cpu is set to offline

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Message-ID: <20080307105138.GA10576@in.ibm.com>
Date:	Fri, 7 Mar 2008 16:21:38 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Yi Yang <yi.y.yang@...el.com>, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [BUG 2.6.25-rc3] scheduler/hotplug: some processes are
	dealocked when cpu is set to offline

On Fri, Mar 07, 2008 at 02:40:49PM +0530, Gautham R Shenoy wrote:
> 
> > 
> > Just to be sure, there were no "bad ->cpu..." messages, yes?
> 
> Hopefully should be able to catch them now. If yes, it's a problem in
> the way we do migration after cpu-hotplug as Yi suggested in an earlier
> mail.
> 
> http://lkml.org/lkml/2008/3/6/437
> 
> This mail from akpm says the same thing.

Yup! There are a quite a few "bad->cpu" messages.
All of them only for watchdog/1.

What surprises me is the fact that the first of  task-hung messages come
after 136 successful cpu-hotplug attempts.

To answer Andrew's question, migration_call() *should* ideally be the
first notifier called, because it's registered with the priority 10.

Unless there's some change that has recently gone in the
notifier_call_chain subsystem that doesn't honour the registration priority
anymore, migration_call() will be called first,
which means the task affinity for watchdog thread is broken and hence
we shouldn't see the message below.

I'll probe to see if there's a change in the call order that's causing
this hang.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
INFO: task watchdog/1:10958 can't get CPU for more than 120 seconds.
bad ->cpu
       f524ffac 00000046 c011befc f5276aa0 f5276bd8 c443db80 00000001 f6130b80 
       f524ff94 00000246 c07130f4 03d28000 00000000 f524ff9c c01438ad f524ffac 
       00000001 c0143a1f 00000000 f524ffd0 c0143a66 00000001 c0119fea 00000000 
Call Trace:
 [<c011befc>] ? cpu_clock+0x4e/0x59
 [<c01438ad>] ? get_timestamp+0x8/0x11
 [<c0143a1f>] ? watchdog+0x0/0x239
 [<c0143a66>] watchdog+0x47/0x239
 [<c0119fea>] ? complete+0x34/0x3e
 [<c0143a1f>] ? watchdog+0x0/0x239
 [<c012f797>] kthread+0x3b/0x64
 [<c012f75c>] ? kthread+0x0/0x64
 [<c01056eb>] kernel_thread_helper+0x7/0x10
 =======================
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



>
> >
> > Oleg.
> 
> -- 
> Thanks and Regards
> gautham

-- 
Thanks and Regards
gautham
--
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