Re: timerfd-add-tfd_notify_clock_set-to-watch-for-clock-changes.patch added to -mm tree

From: Oleg Nesterov <hidden>
Date: 2011-03-11 13:59:25
Also in: lkml

quoted hunk

@@ -218,10 +266,12 @@ SYSCALL_DEFINE4(timerfd_settime, int, uf
 	 * it to the new values.
 	 */
 	for (;;) {
+		spin_lock(&notifiers_lock);
 		spin_lock_irq(&ctx->wqh.lock);
-		if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
+		if (!list_empty(&notifiers_list) || hrtimer_try_to_cancel(&ctx->tmr) >= 0)
 			break;

Confused. Why do we check the global notifiers_list?

IOW. Suppose that this list is not empty and timerfd_settime() is called
without TFD_NOTIFY_CLOCK_SET. Now we are going to reprogramm the timer
without stopping it?

And. What if timerfd_settime(TFD_NOTIFY_CLOCK_SET, utmr => NULL) is called
twice? timerfd_setup() blindly does list_add(), and we corrupt the list, no?

Oleg.

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