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 --- include/linux/stop_machine.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux/stop_machine.h') diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h index 414d924318ce..7b76362b381c 100644 --- a/include/linux/stop_machine.h +++ b/include/linux/stop_machine.h @@ -33,6 +33,7 @@ void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg, struct cpu_stop_work *work_buf); int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg); int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg); +void stop_machine_park(int cpu); #else /* CONFIG_SMP */ -- cgit