----- On Mar 28, 2018, at 8:50 AM, Peter Zijlstra peterz@xxxxxxxxxxxxx wrote: > On Tue, Mar 27, 2018 at 12:05:23PM -0400, Mathieu Desnoyers wrote: >> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h >> index fb5fc458547f..66b070444a7e 100644 >> --- a/kernel/sched/sched.h >> +++ b/kernel/sched/sched.h >> @@ -1249,6 +1249,7 @@ static inline void __set_task_cpu(struct task_struct *p, >> unsigned int cpu) >> #endif >> p->wake_cpu = cpu; >> #endif >> + rseq_migrate(p); >> } > > I think you want that in set_task_cpu(), right next to nr_migrations++. This would miss the __set_task_cpu() call from sched_fork() and wake_up_new_task(). Those cases are not accounted as explicit "migrations", but it does change the CPU of the current task. So if for some weird reason userspace wants to fork() while in a rseq critical section, we want to trigger a rseq restart. Note that rseq_fork() implies rseq_preempt(), but userspace can request to track only migrations for a given rseq critical section (by using the RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT flag), so the rseq_preempt() in rseq_fork() is not enough to restart if a migration between CPUs is done across a fork. An alternative to this would be to call rseq_migrate() in rseq_fork(). Thoughts ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
