From 233e7f267e580fefdeb36628b7efe8bfe056d27c Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Thu, 8 Oct 2015 16:51:31 +0200 Subject: stop_machine: Ensure that a queued callback will be called before cpu_stop_park() cpu_stop_queue_work() checks stopper->enabled before it queues the work, but ->enabled == T can only guarantee cpu_stop_signal_done() if we race with cpu_down(). This is not enough for stop_two_cpus() or stop_machine(), they will deadlock if multi_cpu_stop() won't be called by one of the target CPU's. stop_machine/stop_cpus are fine, they rely on stop_cpus_mutex. But stop_two_cpus() has to check cpu_active() to avoid the same race with hotplug, and this check is very unobvious and probably not even correct if we race with cpu_up(). Change cpu_down() pass to clear ->enabled before cpu_stopper_thread() flushes the pending ->works and returns with KTHREAD_SHOULD_PARK set. Note also that smpboot_thread_call() calls cpu_stop_unpark() which sets enabled == T at CPU_ONLINE stage, so this CPU can't go away until cpu_stopper_thread() is called at least once. This all means that if cpu_stop_queue_work() succeeds, we know that work->fn() will be called. Signed-off-by: Oleg Nesterov Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Linus Torvalds Cc: Mike Galbraith Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Rik van Riel Cc: Tejun Heo Cc: Thomas Gleixner Cc: heiko.carstens@de.ibm.com Link: http://lkml.kernel.org/r/20151008145131.GA18139@redhat.com Signed-off-by: Ingo Molnar --- kernel/cpu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/cpu.c') diff --git a/kernel/cpu.c b/kernel/cpu.c index 050c63472f03..c85df2775b73 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -344,7 +344,7 @@ static int take_cpu_down(void *_param) /* Give up timekeeping duties */ tick_handover_do_timer(); /* Park the stopper thread */ - kthread_park(current); + stop_machine_park((long)param->hcpu); return 0; } -- cgit v1.2.3