Module: xenomai-head Branch: master Commit: 7ea2e7bd261de0f8b7ce41e530e2f1fecda4bf43 URL: http://git.xenomai.org/?p=xenomai-head.git;a=commit;h=7ea2e7bd261de0f8b7ce41e530e2f1fecda4bf43
Author: Philippe Gerum <r...@xenomai.org> Date: Sat Aug 28 17:29:42 2010 +0200 nucleus/sched: prevent remote wakeup from triggering a debug assertion Jan: ---- "The task that was scheduled in without XNRESCHED set locally has been woken up by a remote CPU. The waker requeued the task and set the resched condition for itself and in the resched proxy mask for the remote CPU. But there is at least one place in the Xenomai code where we drop the nklock between xnsched_set_resched and xnpod_schedule: do_taskexit_event (I bet there are even more). Now the resched target CPU runs into a timer handler, issues xnpod_schedule unconditionally, and happens to find the woken-up task before it is actually informed via an IPI." Gilles: ------- "Yes, and whether we set the bit and call xnpod_schedule atomically does not really matter either: the IPI takes time to propagate, and since xnarch_send_ipi does not wait for the IPI to have been received on the remote CPU, there is no guarantee that xnpod_schedule could not have been called in the mean time. More importantly, since in order to do an action on a remote xnsched_t, we need to hold the nklock, is there any point in not setting the XNRESCHED bit on that distant structure, at the same time as when we set the cpu bit on the local sched structure mask and send the IPI? This way, setting the XNRESCHED bit in the IPI handler would no longer be necessary, and we would avoid the race." What this patch does is exactly that, in an attempt to make the remote rescheduling code safer and simpler: - by testing XNSCHED in __xnpod_test_resched() instead of the resched bitmask for the current CPU; this bitmask is now only used to broadcast the IPI to the CPUs pending a reschedule, from the local processor POV. - by setting the XNSCHED bit immediately in the remote scheduler's status, which fixes the unwanted assertion. See there for the discussion regarding this issue: https://mail.gna.org/public/xenomai-core/2010-08/msg00084.html --- include/nucleus/sched.h | 6 ++++-- ksrc/nucleus/pod.c | 6 +----- 2 files changed, 5 insertions(+), 7 deletions(-) diff --git a/include/nucleus/sched.h b/include/nucleus/sched.h index c46ba4b..d608bdf 100644 --- a/include/nucleus/sched.h +++ b/include/nucleus/sched.h @@ -177,15 +177,17 @@ static inline int xnsched_self_resched_p(struct xnsched *sched) /* Set self resched flag for the given scheduler. */ #define xnsched_set_self_resched(__sched__) do { \ - xnarch_cpu_set(xnsched_cpu(__sched__), (__sched__)->resched); \ setbits((__sched__)->status, XNRESCHED); \ } while (0) /* Set specific resched flag into the local scheduler mask. */ #define xnsched_set_resched(__sched__) do { \ xnsched_t *current_sched = xnpod_current_sched(); \ - xnarch_cpu_set(xnsched_cpu(__sched__), current_sched->resched); \ setbits(current_sched->status, XNRESCHED); \ + if (current_sched != (__sched__)) { \ + xnarch_cpu_set(xnsched_cpu(__sched__), current_sched->resched); \ + setbits((__sched__)->status, XNRESCHED); \ + } \ } while (0) void xnsched_zombie_hooks(struct xnthread *thread); diff --git a/ksrc/nucleus/pod.c b/ksrc/nucleus/pod.c index df6009f..678d667 100644 --- a/ksrc/nucleus/pod.c +++ b/ksrc/nucleus/pod.c @@ -285,7 +285,6 @@ void xnpod_schedule_handler(void) /* Called with hw interrupts off. */ xnshadow_rpi_check(); } #endif /* CONFIG_SMP && CONFIG_XENO_OPT_PRIOCPL */ - xnsched_set_self_resched(sched); xnpod_schedule(); } @@ -2159,10 +2158,7 @@ static inline void xnpod_switch_to(xnsched_t *sched, static inline int __xnpod_test_resched(struct xnsched *sched) { - int cpu = xnsched_cpu(sched), resched; - - resched = xnarch_cpu_isset(cpu, sched->resched); - xnarch_cpu_clear(cpu, sched->resched); + int resched = testbits(sched->status, XNRESCHED); #ifdef CONFIG_SMP /* Send resched IPI to remote CPU(s). */ if (unlikely(xnsched_resched_p(sched))) { _______________________________________________ Xenomai-git mailing list Xenomai-git@gna.org https://mail.gna.org/listinfo/xenomai-git
