Subject: Re: PATCH: Fix race in cpu_down (hotplug cpu)
From: Nigel Cunningham <ncunningham@cyclades.com>
Reply-To: ncunningham@cyclades.com
To: vatsa@in.ibm.com
Cc: Li Shaohua <shaohua.li@intel.com>, Andrew Morton <akpm@osdl.org>,
       Linus Torvalds <torvalds@osdl.org>,
       Zwane Mwaikambo <zwane@arm.linux.org.uk>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Rusty Russell <rusty@rustcorp.com.au>, Ingo Molnar <mingo@elte.hu>
In-Reply-To: <20050919055715.GE8653@in.ibm.com>
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Organization: Cyclades
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Date: Mon, 19 Sep 2005 16:11:11 +1000
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Hi.

On Mon, 2005-09-19 at 15:57, Srivatsa Vaddagiri wrote:
> On Mon, Sep 19, 2005 at 01:31:27PM +0800, Shaohua Li wrote:
> > A CPU is idle and then is preempted and starting offline CPU. After
> > calling stop_machine_run, the CPU goes into idle and it will resume last
> > idle loop. If the CPU is broken at specific point, then the CPU will
> > continue executing previous idle and have no chance to call play_dead.
> 
> Ok, that makes sense. Nigel, could you confirm which idle routine you are 
> using?

>From dmesg:

monitor/mwait feature present.
using mwait in idle threads.

> > Am I missing anything? Nigel's patch seems can fix the situation for
> > mwait_idle and poll_idle but can't fix for default_idle in i386 to me.
> 
> I would say the right fix here is for poll_idle and mwait_idle (& similar
> other idle routines) to monitor 'cpu_offline' flag in addition to need_resched 
> flag, rather than what Nigel has suggested. 

Ok, but what about default_idle?

Regards,

Nigel

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