linux-kernel - Re: [tip:locking/core] locking/pvqspinlock: Replace xchg() by the more descriptive set

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

Message-ID: <20150512130043.GF16478@twins.programming.kicks-ass.net>
Date:	Tue, 12 May 2015 15:00:43 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Douglas Hatch <doug.hatch@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Waiman Long <Waiman.Long@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Norton, Scott J" <scott.norton@...com>,
	Peter Anvin <hpa@...or.com>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:locking/core] locking/pvqspinlock: Replace xchg() by the
 more descriptive set_mb()

On Tue, May 12, 2015 at 10:45:29AM +0200, Peter Zijlstra wrote:
> On Mon, May 11, 2015 at 10:50:42AM -0700, Linus Torvalds wrote:
> > On Mon, May 11, 2015 at 7:54 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > >
> > > Hmm, so I looked at the set_mb() definitions and I figure we want to do
> > > something like the below, right?
> > 
> > I don't think you need to do this for the non-smp cases. 
> 
> Well, its the store tearing thing again, we use WRITE_ONCE() in
> smp_store_release() for the same reason. We want it to be a single
> store.
> 
> > The whole
> > thing is about smp memory ordering, so on UP you don't even need the
> > WRITE_ONCE(), much less a barrier.

Ah, you meant the memory barrier; indeed, a compiler barrier is
sufficient. I got somewhat confused between Waiman's email and barrier
and barrier() (again!).


--
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/