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

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Message-ID: <alpine.LRH.2.00.1408210127150.12153@twin.jikos.cz>
Date:	Thu, 21 Aug 2014 01:27:56 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	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, 10 Jun 2014, Jiri Kosina wrote:

> We have been chasing a memory corruption bug, which turned out to be 
> caused by very old gcc (4.3.4), which happily turned conditional load into 
> a non-conditional one, and that broke correctness (the condition was met 
> only if lock was held) and corrupted memory.
> 
> This particular problem with that particular code did not happen when 
> never gccs were used. I've brought this up with our gcc folks, as I wanted 
> to make sure that this can't really happen again, and it turns out it 
> actually can.

For the record (and for mailinglist archives to catch this information) -- 
the default has been changed for gcc 4.10 to a sane value (0).
 
I'd however suggest we keep changes made by commit 69102311a ("./Makefile:
tell gcc optimizer to never introduce new data races") for rather a long  
time.

-- 
Jiri Kosina
SUSE Labs

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