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 <[email protected]>
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);
-
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