Messages in this thread Patch in this message | | | Subject | posix-timers overrun broken? | From | Milan Svoboda <> | Date | Wed, 7 Feb 2007 14:36:12 +0100 |
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Hi,
I'm creating a driver for timer on ixp4xx (there are two hardware timers). It shall use posix api so I looked at the only driver that implements it in kernel: drivers/char/mmtimer.c. My driver uses almost the same logic that handles overruns.
However, I found that receiving of number of overruns in waitsiginfo is somewhat broken.
Linux-2.6.20:
Look at posix_timer_event - this is called when interrupt wants to signal the thread that event happend. The very first operation there is memset(&timr->sigq->info, 0, sizeof(siginfo_t)); this clears all info members - si.overrun included. Then send_sigqueue or send_group_sigqueue is called. They both check if it's SI_TIMER and if so, they increase si.overrun if the signal is already queued.
But if the next interrupt arrives before function collect_signal is called to actually deliver the siginfo_t to userspace, the si.overrun is cleared in posix_timer_event and we have just forgotten one overrun...
Am I wrong?
Patch follows, but please note that it is more to describe the problem than solve the problem in proper way...
Please, CC me, I'm not subscribed on the list.
Signed-off-by: Milan Svoboda <msvoboda@ra.rockwell.com>
Index: linux/kernel/posix-timers.c =================================================================== --- linux.orig/kernel/posix-timers.c +++ linux/kernel/posix-timers.c @@ -298,7 +298,10 @@ void do_schedule_next_timer(struct sigin int posix_timer_event(struct k_itimer *timr,int si_private) { + int overrun = timr->sigq->info.si_overrun; memset(&timr->sigq->info, 0, sizeof(siginfo_t)); + timr->sigq->info.si_overrun = overrun; + timr->sigq->info.si_sys_private = si_private; /* Send signal to the process that owns this timer.*/ @@ -407,6 +410,7 @@ static struct k_itimer * alloc_posix_tim kmem_cache_free(posix_timers_cache, tmr); tmr = NULL; } + tmr->sigq->info.si_overrun = 0; return tmr; } Index: linux/kernel/signal.c =================================================================== --- linux.orig/kernel/signal.c +++ linux/kernel/signal.c @@ -402,6 +402,7 @@ static int collect_signal(int sig, struc if (first) { list_del_init(&first->list); copy_siginfo(info, &first->info); + first->info.si_overrun = 0; __sigqueue_free(first); if (!still_pending) sigdelset(&list->signal, sig); - 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/
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