Messages in this thread | | | Date | Tue, 04 May 2010 09:03:28 +0200 | From | Tejun Heo <> | Subject | Re: [PATCH 1/4] cpu_stop: implement stop_cpu[s]() |
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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
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