linux-kernel - Re: migrate_disable() race with cpu hotplug?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <alpine.LFD.2.02.1107280853500.2660@ionos>
Date:	Thu, 28 Jul 2011 08:55:07 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Yong Zhang <yong.zhang0@...il.com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: migrate_disable() race with cpu hotplug?

On Thu, 28 Jul 2011, Yong Zhang wrote:

> On Wed, Jul 27, 2011 at 11:52:18PM +0200, Thomas Gleixner wrote:
> > On Tue, 26 Jul 2011, Yong Zhang wrote:
> > 
> > > When reading the code, I'm afraid there is a race between migrate_disable()
> > > and cpu hotplug. A scenario will like below:
> > > 
> > > 	CPU0			CPU1
> > > _cpu_down();
> > >   cpu_unplug_begin();
> > >     wait_for_completion()
> > >   			sync_unplug_thread();
> > > 			  complete();
> > > 			race_window? /*
> > > 				      * migrate_disable() will
> > > 				      * not take effect since
> > > 				      * hotplug is in progress
> > > 				      */
> > 
> > Rightfully so. The caller will just block on the cpu_hotplug.lock
> > mutex until the unplug operation will be done.
> 
> Yup, just notice the mutex_lock/mutex_unlock in pin_current_cpu().
> 
> But if the caller block on mutex_lock() then waked up, it's possible
> that it's been migrated to another cpu. So in the 'retry' loop, we
> should reget hotplug_pcp.

Ooops, that was the original plan. I somehow managed to fatfinger
that. Good catch.
 
Thanks,

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