linux-kernel - Re: [PATCH] tell gcc optimizer to never introduce new data races

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Message-ID: <20140610151735.GH19001@tucnak.redhat.com>
Date:	Tue, 10 Jun 2014 17:17:35 +0200
From:	Jakub Jelinek <jakub@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Marek Polacek <polacek@...hat.com>, Jiri Kosina <jkosina@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Martin Jambor <mjambor@...e.cz>, Petr Mladek <pmladek@...e.cz>,
	linux-kernel@...r.kernel.org, gcc@....gnu.org
Subject: Re: [PATCH] tell gcc optimizer to never introduce new data races

On Tue, Jun 10, 2014 at 05:13:29PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 10, 2014 at 05:04:55PM +0200, Marek Polacek wrote:
> > On Tue, Jun 10, 2014 at 04:53:27PM +0200, Peter Zijlstra wrote:
> > > On Tue, Jun 10, 2014 at 03:23:36PM +0200, Jiri Kosina wrote:
> > > > +# Tell gcc to never replace conditional load with a non-conditional one
> > > > +KBUILD_CFLAGS	+= $(call cc-option,--param allow-store-data-races=0)
> > > > +
> > > 
> > > Why do we not want: -fmemory-model=safe? And should we not at the very
> > > least also disable packed-store-data-races?
> > 
> > Note that the option does not exist, even though it is mentioned in the
> > documentation.
> 
> Urgh.. ok. Any word on the packed-store-data thing?

That is recognized, undocumented and never used in the compiler (not in 4.7
or any later release till now).  Most of the spots in the compiler that
could introduce data races were actually just changed, there is (already
since 4.7) just a single conditional on the --param allow-store-data-races=X
value.

	Jakub
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