Messages in this thread | | | Date | Sat, 25 Dec 2010 10:12:09 +0800 | From | Yong Zhang <> | Subject | Re: [PATCH] fix unsafe operation in high resolution timer |
| |
On Fri, Dec 24, 2010 at 10:28:52PM +0800, Hillf Danton wrote: > On Fri, Dec 24, 2010 at 3:17 PM, Yong Zhang <yong.zhang0@gmail.com> wrote: > > On Thu, Dec 23, 2010 at 9:29 PM, Hillf Danton <dhillf@gmail.com> wrote: > >> After calling the callback function of hrtimer, the timer could become > >> unreliable in corner cases where the timer will no longer be queued > >> and the mm segment, in which the timer is embedded, could be reclaimed > >> in the callback. > >> > >> The unreliability is fixed by checking the result of callback before > >> operating the timer again. > > > > Though the patch is buggy. But it actually explores a real problem. > > > > Would you please finger out why the patch is buggy?
No problem.
Actually the patch change the behavior of current hrtimer. See comments below :)
> >> --- > >> > >> --- a/kernel/hrtimer.c 2010-11-01 19:54:12.000000000 +0800 > >> +++ b/kernel/hrtimer.c 2010-12-23 21:17:02.000000000 +0800 > >> @@ -1225,6 +1225,7 @@ static void __run_hrtimer(struct hrtimer > >> raw_spin_unlock(&cpu_base->lock); > >> trace_hrtimer_expire_entry(timer, now); > >> restart = fn(timer); > >> + if (restart != HRTIMER_NORESTART) > >> trace_hrtimer_expire_exit(timer); > >> raw_spin_lock(&cpu_base->lock); > >> > >> @@ -1236,11 +1237,8 @@ static void __run_hrtimer(struct hrtimer > >> if (restart != HRTIMER_NORESTART) { > >> BUG_ON(timer->state != HRTIMER_STATE_CALLBACK); > >> enqueue_hrtimer(timer, base); > >> + timer->state &= ~HRTIMER_STATE_CALLBACK;
HRTIMER_STATE_CALLBACK is only cleared for RESTART hrtimer with your modification.
> >> } > >> - > >> - WARN_ON_ONCE(!(timer->state & HRTIMER_STATE_CALLBACK)); > >> - > >> - timer->state &= ~HRTIMER_STATE_CALLBACK;
But for a hrtimer which is not free in its callback, like a static defined one. the hrtimer could be referenced at the same time. So here you cann't just delete the two lines.
Thanks, Yong -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |