linux-kernel - Re: [PATCH 10/11] qspinlock: Paravirt support

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 for Android: free password hash cracker in your pocket

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

Date:	Mon, 7 Jul 2014 17:20:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Waiman Long <waiman.long@...com>, tglx@...utronix.de,
	mingo@...nel.org, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	xen-devel@...ts.xenproject.org, kvm@...r.kernel.org,
	paolo.bonzini@...il.com, konrad.wilk@...cle.com,
	boris.ostrovsky@...cle.com, paulmck@...ux.vnet.ibm.com,
	riel@...hat.com, torvalds@...ux-foundation.org,
	raghavendra.kt@...ux.vnet.ibm.com, david.vrabel@...rix.com,
	oleg@...hat.com, gleb@...hat.com, scott.norton@...com,
	chegu_vinod@...com
Subject: Re: [PATCH 10/11] qspinlock: Paravirt support

On Wed, Jun 18, 2014 at 02:03:12PM +0200, Paolo Bonzini wrote:
> Il 17/06/2014 00:08, Waiman Long ha scritto:
> >>+void __pv_queue_unlock(struct qspinlock *lock)
> >>+{
> >>+	int val = atomic_read(&lock->val);
> >>+
> >>+	native_queue_unlock(lock);
> >>+
> >>+	if (val & _Q_LOCKED_SLOW)
> >>+		___pv_kick_head(lock);
> >>+}
> >>+
> >
> >Again a race can happen here between the reading and writing of the lock
> >value. I can't think of a good way to do that without using cmpxchg.
> 
> Could you just use xchg on the locked byte?

I'll have to, indeed. This is racy.

Content of type "application/pgp-signature" skipped