Date: Fri, 11 Mar 2011 17:08:57 +0200
From: Alexander Shishkin <virtuoso@slind.org>
To: Oleg Nesterov <oleg@redhat.com>
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, Alexander Shishkin <virtuoso@slind.org>
Subject: Re:
 timerfd-add-tfd_notify_clock_set-to-watch-for-clock-changes.patch added to
 -mm tree
Message-ID: <20110311150857.GJ11410@shisha.kicks-ass.net>
References: <20110311135023.GA23552@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20110311135023.GA23552@redhat.com>
User-Agent: Mutt/1.5.20 (2009-06-14)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1220
Lines: 35

On Fri, Mar 11, 2011 at 02:50:23PM +0100, Oleg Nesterov wrote:
> > @@ -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?

You're right, it's a bug, should be &ctx->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?

Another catch.

There will be a quite a bit of rework required, though, considering tglx's
comments.

Thanks!
--
Alex
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/