linux-kernel - Re: + generic-ipi-fix-the-race-between-generic_smp_call_function_-and-hotplug

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Message-Id: <1253597553.2519.8.camel@sbs-t61>
Date:	Mon, 21 Sep 2009 22:32:33 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mm-commits@...r.kernel.org" <mm-commits@...r.kernel.org>,
	"jens.axboe@...cle.com" <jens.axboe@...cle.com>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"nickpiggin@...oo.com.au" <nickpiggin@...oo.com.au>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: +
 generic-ipi-fix-the-race-between-generic_smp_call_function_-and-hotplug_cfd.patch
 added to -mm tree

On Sun, 2009-09-20 at 21:04 -0700, Xiao Guangrong wrote:
> 
> Suresh Siddha wrote:
> > 
> > I am referring to the missing csd_lock_wait() here that you had in the
> > first version of your patch. Let's say, if cpu X is going offline, we
> > need to ensure that the smp_call_function() initiated by cpu X (i.e.,
> > smp_call_function IPI sent to some other cpu's from cpu X) got serviced
> > before cpu X goes offline. We can't do csd_lock_wait() here, as that
> > might deadlock (as all the other cpu's are already in stop machine with
> > interrupts disabled).
> > 
> 
> It not happen because the preemption is disabled while send IPI request and
> can't schedule to stop machine path, it also stop cpu down.

Xiao, I am getting confused. I am referring to case '1' mentioned by you
here http://marc.info/?l=linux-kernel&m=125265516529139&w=2

thanks,
suresh

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