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From: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
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
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	[thread overview]
Message-ID: <20110311135023.GA23552@redhat.com> (raw)

> @@ -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.

WARNING: multiple messages have this Message-ID (diff)
From: Oleg Nesterov <oleg@redhat.com>
To: Alexander Shishkin <virtuoso@slind.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@suse.de>,
	Feng Tang <feng.tang@intel.com>, Michael Tokarev <mjt@tls.msk.ru>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	John Stultz <johnstul@us.ibm.com>,
	Chris Friesen <chris.friesen@genband.com>,
	Kay Sievers <kay.sievers@vrfy.org>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Artem Bityutskiy <dedekind1@gmail.com>,
	Davide Libenzi <davidel@xmailserver.org>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	linux-api@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.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	[thread overview]
Message-ID: <20110311135023.GA23552@redhat.com> (raw)

> @@ -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.


             reply	other threads:[~2011-03-11 13:50 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-03-11 13:50 Oleg Nesterov [this message]
2011-03-11 13:50 ` timerfd-add-tfd_notify_clock_set-to-watch-for-clock-changes.patch added to -mm tree Oleg Nesterov
     [not found] ` <20110311135023.GA23552-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2011-03-11 15:08   ` Alexander Shishkin
2011-03-11 15:08     ` Alexander Shishkin
2011-03-11 16:23   ` Thomas Gleixner
2011-03-11 16:23     ` Thomas Gleixner

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