On Wed, Mar 28, 2018 at 10:47:54AM -0400, Mathieu Desnoyers wrote: > ----- 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(). Correct; but since those are _new_ tasks they _SHOULD_ not have an active RSEQ to begin with. > 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. If at all possible I would make it SIGSEGV when issueing SYSCALL()s from within an RSEQ. > An alternative to this would be to call rseq_migrate() in rseq_fork(). > > Thoughts ? Yes, don't try and support that at all. It's _insane_. -- 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
