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

1 files changed, 14 insertions, 5 deletions

diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index 9a21681aa80f..e36d5798cbff 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -289,21 +289,29 @@ void do_schedule_next_timer(struct siginfo *info)
                 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;
@@ -435,6 +443,7 @@ static struct k_itimer * alloc_posix_timer(void)
                 kmem_cache_free(posix_timers_cache, tmr);
                 tmr = NULL;
         }
+        memset(&tmr->sigq->info, 0, sizeof(siginfo_t));
         return tmr;
 }