linux-kernel - Re: interesting commit about llvm introducing barrier

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Message-ID: <1605703.GSn7kbzMda@tauon.atsec.com>
Date:	Tue, 23 Feb 2016 15:46:19 +0100
From:	Stephan Mueller <smueller@...onox.de>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Will Deacon <will.deacon@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Theodore Ts'o <tytso@....edu>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	mancha security <mancha1@...o.com>,
	Mark Charlebois <charlebm@...il.com>,
	Behan Webster <behanw@...verseincode.com>,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: interesting commit about llvm introducing barrier_data()

Am Dienstag, 23. Februar 2016, 14:32:43 schrieb Mathieu Desnoyers:

Hi Mathieu,

> ----- On Feb 23, 2016, at 9:23 AM, Paul E. McKenney 
paulmck@...ux.vnet.ibm.com wrote:
> > On Tue, Feb 23, 2016 at 02:02:26PM +0000, Mathieu Desnoyers wrote:
> >> commit 7829fb09a2b4268b30dd9bc782fa5ebee278b137
> >> Author: Daniel Borkmann <daniel@...earbox.net>
> >> Date:   Thu Apr 30 04:13:52 2015 +0200
> >> 
> >>     lib: make memzero_explicit more robust against dead store elimination
> >> 
> >> ^ interesting commit. Any idea on the impact of this on kernel RCU
> >> implementation and liburcu cmm_barrier() ?
> > 
> > First I knew of it!  But I bet that more like this are needed.  ;-)
> 
> I recommend you check my IRC discussion with peterz on the matter of
> this new "barrier_data()".
> 
The key idea of the memzero_explicit is about forcing the compiler to do a 
memset.

See the trivial test attached.

Ciao
Stephan
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