From mboxrd@z Thu Jan  1 00:00:00 1970
From: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re:
	timerfd-add-tfd_notify_clock_set-to-watch-for-clock-changes.patch
	added to -mm tree
Date: Fri, 11 Mar 2011 14:50:23 +0100
Message-ID: <20110311135023.GA23552@redhat.com>
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To: Alexander Shishkin <virtuoso-0lOfPCoBze7YtjvyW6yDsg@public.gmane.org>
Cc: Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>, Alexander Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>, Greg Kroah-Hartman <gregkh-l3A5Bk7waGM@public.gmane.org>, Feng Tang <feng.tang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Michael Tokarev <mjt-XAri/EZa3C4vJsYlp49lxw@public.gmane.org>, Marcelo Tosatti <mtosatti-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, John Stultz <johnstul-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>, Chris Friesen <chris.friesen-b7o/lNNmKxtBDgjK7y7TUQ@public.gmane.org>, Kay Sievers <kay.sievers-tD+1rO4QERM@public.gmane.org>, "Kirill A. Shutemov" <kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org>, Artem Bityutskiy <dedekind1-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Davide Libenzi <davidel-AhlLAIvw+VEjIGhXcJzhZg@public.gmane.org>, Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
List-Id: linux-api@vger.kernel.org

> @@ -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.