Messages in this thread Patch in this message |  | | Date | Fri, 28 Feb 2014 13:39:05 +0100 | From | Peter Zijlstra <> | Subject | Re: smp_call_function_single with wait=0 considered harmful |
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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 <prarit@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Mel Gorman <mgorman@suse.de> Signed-off-by: Peter Zijlstra <peterz@infradead.org> --- kernel/stop_machine.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index 84571e09c907..01fbae5b97b7 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -293,7 +293,7 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void * */ smp_call_function_single(min(cpu1, cpu2), &irq_cpu_stop_queue_work, - &call_args, 0); + &call_args, 1); lg_local_unlock(&stop_cpus_lock); preempt_enable();
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