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

[Oleg Nesterov]

> @@ -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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