From: Tejun Heo <tj@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@elte.hu, linux-kernel@vger.kernel.org, x86@kernel.org,
oleg@redhat.com, rusty@rustcorp.com.au, sivanich@sgi.com,
heiko.carstens@de.ibm.com, dipankar@in.ibm.com,
josh@freedesktop.org, paulmck@linux.vnet.ibm.com,
akpm@linux-foundation.org, arjan@linux.intel.com,
torvalds@linux-foundation.org
Subject: Re: [PATCH 1/4] cpu_stop: implement stop_cpu[s]()
Date: Tue, 04 May 2010 09:03:28 +0200 [thread overview]
Message-ID: <4BDFC6C0.7020009@kernel.org> (raw)
In-Reply-To: <4BDFC06B.4020805@kernel.org>
On 05/04/2010 08:36 AM, Tejun Heo wrote:
> On 05/03/2010 03:26 PM, Peter Zijlstra wrote:
>> On Thu, 2010-04-22 at 18:09 +0200, Tejun Heo wrote:
>>> +static int cpu_stopper_thread(void *data)
>>> +{
>>> + struct cpu_stopper *stopper = data;
>>
>> BUG_ON(stopper != __get_cpu_var(cpu_stopper)); ?
>
> Added.
Now that I think more about it, there's a subtle race condition with
the above BUG_ON(). Stoppers are prepared by CPU_UP_PREPARE and
started by CPU_ONLINE but brought down by CPU_DEAD. IOW, they're
allowed to run detached from their designated CPUs between CPU_DYING
and CPU_DEAD (the reponsibility of guaranteeing target cpus's onliness
is on the callers). So, the above BUG_ON() might trigger spuriously
if a cpu goes down after brought online before its cpu_stopper had a
chance to pass through the BUG_ON() test.
Thanks.
--
tejun
next prev parent reply other threads:[~2010-05-04 7:04 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-22 16:09 [PATCHSET sched/core] cpu_stop: implement and use cpu_stop Tejun Heo
2010-04-22 16:09 ` [PATCH 1/4] cpu_stop: implement stop_cpu[s]() Tejun Heo
2010-05-03 13:26 ` Peter Zijlstra
2010-05-04 6:36 ` Tejun Heo
2010-05-03 13:26 ` Peter Zijlstra
2010-05-04 6:36 ` Tejun Heo
2010-05-04 7:03 ` Tejun Heo [this message]
2010-05-04 8:43 ` Peter Zijlstra
2010-05-03 13:26 ` Peter Zijlstra
2010-05-04 6:40 ` Tejun Heo
2010-05-04 6:55 ` Tejun Heo
2010-04-22 16:09 ` [PATCH 2/4] stop_machine: reimplement using cpu_stop Tejun Heo
2010-04-22 16:09 ` [PATCH 3/4] scheduler: replace migration_thread with cpu_stop Tejun Heo
2010-05-03 13:26 ` Peter Zijlstra
2010-05-04 7:17 ` Tejun Heo
2010-05-04 12:45 ` Peter Zijlstra
2010-05-04 12:49 ` Tejun Heo
2010-04-22 16:09 ` [PATCH 4/4] scheduler: kill paranoia check in synchronize_sched_expedited() Tejun Heo
-- strict thread matches above, loose matches on Subject: below --
2010-05-04 13:47 [PATCHSET sched/core] cpu_stop: implement and use cpu_stop, take#2 Tejun Heo
2010-05-04 13:47 ` [PATCH 1/4] cpu_stop: implement stop_cpu[s]() Tejun Heo
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