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] [thread-next>] [day] [month] [year] [list]
Date:	Fri, 11 Dec 2015 14:48:03 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Will Deacon <will.deacon@....com>
Cc:	Andrew Pinski <andrew.pinski@...iumnetworks.com>,
	Davidlohr Bueso <dbueso@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, david.daney@...ium.com
Subject: Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release
 semantics) causing failures on arm64 (ThunderX)

On Fri, Dec 11, 2015 at 01:33:14PM +0000, Will Deacon wrote:
> On Fri, Dec 11, 2015 at 01:26:47PM +0100, Peter Zijlstra wrote:

> > While we're there, the acquire in osq_wait_next() seems somewhat ill
> > documented too.
> > 
> > I _think_ we need ACQUIRE semantics there because we want to strictly
> > order the lock-unqueue A,B,C steps and we get that with:
> > 
> >  A: SC
> >  B: ACQ
> >  C: Relaxed
> > 
> > Similarly for unlock we want the WRITE_ONCE to happen after
> > osq_wait_next, but in that case we can even rely on the control
> > dependency there.
> 
> Even for the lock-unqueue case, isn't B->C ordered by a control dependency
> because C consists only of stores?

Hmm, indeed. So we could go fully relaxed on it I suppose, since the
same is true for the unlock site.


--
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/

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ