On 02/28/2014 07:39 AM, Peter Zijlstra wrote:
> On Fri, Feb 28, 2014 at 01:26:24PM +0100, Peter Zijlstra wrote:
>> On Wed, Dec 04, 2013 at 08:46:27AM -0800, Christoph Hellwig wrote:
>>> kernel/stop_machine.c:stop_two_cpus()
>>
>> That site should work with .wait=1 just fine, but given the above, the
>> .wait=0 doesn't appear problematic at all.
>
> Scratch that; its broken, but not because of smp_call_function_single().
>
> ---
> Subject: stop_machine: Fix^2 race between stop_two_cpus() and stop_cpus()
>
> We must use smp_call_function_single(.wait=1) for the
> irq_cpu_stop_queue_work() to ensure the queueing is actually done under
> stop_cpus_lock. Without this we could have dropped the lock by the time
> we do the queueing and get the race we tried to fix.
>
> Fixes: 7053ea1a34fa ("stop_machine: Fix race between stop_two_cpus() and
> stop_cpus()")
> Cc: Prarit Bhargava <pra...@redhat.com>
> Cc: Rik van Riel <r...@redhat.com>
> Cc: Mel Gorman <mgor...@suse.de>
> Signed-off-by: Peter Zijlstra <pet...@infradead.org>
Reviewed-by: Prarit Bhargava <pra...@redhat.com>
P.
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