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: <20150714125146.GJ16213@arm.com>
Date:	Tue, 14 Jul 2015 13:51:46 +0100
From:	Will Deacon <will.deacon@....com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [RFC PATCH v2] memory-barriers: remove
 smp_mb__after_unlock_lock()

Hi Paul,

On Tue, Jul 14, 2015 at 01:45:40PM +0100, Paul E. McKenney wrote:
> On Tue, Jul 14, 2015 at 11:04:29AM +0100, Will Deacon wrote:
> > Given that RCU is currently the only user of this barrier, how would you
> > feel about making the barrier local to RCU and not part of the general
> > memory-barrier API?
> 
> In theory, no objection.  Your thought is to leave the definitions where
> they are, mark them as being used only by RCU, and removing mention from
> memory-barriers.txt?  Or did you have something else in mind?

Actually, I was thinking of defining them in an RCU header file with an
#ifdef CONFIG_POWERPC for the smb_mb() version. Then you could have a big
comment describing the semantics, or put that in an RCU Documentation file
instead of memory-barriers.txt.

That *should* then mean we notice anybody else trying to use the barrier,
because they'd need to send patches to either add something equivalent
or move the definition out again.

> > My main reason for proposing its removal is because I don't want to see
> > it being used (incorrectly) all over the place to order the new RELEASE
> > and ACQUIRE operations I posted separately, at which point we have to try
> > fixing up all the callers or retrofitting some semantics. It doesn't help
> > that memory-barriers.txt lumps things like LOCK and ACQUIRE together,
> > whereas this barrier is currently only intended to be used in conjunction
> > with the former.
> 
> Heh!  That lumping was considered to be a feature at the time.  ;-)

Oh, I'm sure it was added with good intentions!

Will
--
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/