Merge branch 'timers-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'timers-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
posix-timers: fix posix_timer_event() vs dequeue_signal() race
posix-timers: do_schedule_next_timer: fix the setting of ->si_overrun

kernel/posix-timers.c

···
 		else
 			schedule_next_timer(timr);
 
-		info->si_overrun = timr->it_overrun_last;
+		info->si_overrun += timr->it_overrun_last;
 	}
 
 	if (timr)
 		unlock_timer(timr, flags);
 }
 
-int posix_timer_event(struct k_itimer *timr,int si_private)
+int posix_timer_event(struct k_itimer *timr, int si_private)
 {
-	memset(&timr->sigq->info, 0, sizeof(siginfo_t));
+	/*
+	 * FIXME: if ->sigq is queued we can race with
+	 * dequeue_signal()->do_schedule_next_timer().
+	 *
+	 * If dequeue_signal() sees the "right" value of
+	 * si_sys_private it calls do_schedule_next_timer().
+	 * We re-queue ->sigq and drop ->it_lock().
+	 * do_schedule_next_timer() locks the timer
+	 * and re-schedules it while ->sigq is pending.
+	 * Not really bad, but not that we want.
+	 */
 	timr->sigq->info.si_sys_private = si_private;
-	/* Send signal to the process that owns this timer.*/
 
 	timr->sigq->info.si_signo = timr->it_sigev_signo;
-	timr->sigq->info.si_errno = 0;
 	timr->sigq->info.si_code = SI_TIMER;
 	timr->sigq->info.si_tid = timr->it_id;
 	timr->sigq->info.si_value = timr->it_sigev_value;
···
 		kmem_cache_free(posix_timers_cache, tmr);
 		tmr = NULL;
 	}
+	memset(&tmr->sigq->info, 0, sizeof(siginfo_t));
 	return tmr;
 }
 

kernel/signal.c

···
 		q->info.si_overrun++;
 		goto out;
 	}
+	q->info.si_overrun = 0;
 
 	signalfd_notify(t, sig);
 	pending = group ? &t->signal->shared_pending : &t->pending;