linux-kernel - Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock

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]

Message-ID: <1437087265.28088.53.camel@kernel.crashing.org>
Date:	Fri, 17 Jul 2015 08:54:25 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Michael Ellerman <mpe@...erman.id.au>,
	Will Deacon <will.deacon@....com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH v2] memory-barriers: remove
 smp_mb__after_unlock_lock()

On Thu, 2015-07-16 at 08:11 -0700, Paul E. McKenney wrote:
> > So isync in lock in architecturally incorrect, despite being what
> the
> > architecture recommends using, yay !
> 
> Well, the architecture isn't expecting that crazies like myself would
> want to have an unlock-lock provide ordering to some CPU not holding
> the lock.  :-/

Yes, isync in lock effectively allows any load or store before the lock
to leak into the lock and get re-ordered with things in there.

lwsync leaves us exposed to the re-order inside the LL/SC of a
subsequent load.

So to get the full barrier semantic, the only option is a full sync,
either in lock or unlock. Instinctively I prefer in lock but there's
an argument to have it in unlock so we can get rid of the iosync
business.

Ben.


--
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/