linux-kernel - Re: [PATCH 1/3] sched, timer: Remove usages of ACCESS

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: <20150416190208.GD23123@twins.programming.kicks-ass.net>
Date:	Thu, 16 Apr 2015 21:02:08 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>, Mel Gorman <mel@....ul.ie>,
	Rik van Riel <riel@...hat.com>,
	Jason Low <jason.low2@...com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mel Gorman <mgorman@...e.de>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	hideaki.kimura@...com, Aswin Chandramouleeswaran <aswin@...com>,
	Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH 1/3] sched, timer: Remove usages of ACCESS_ONCE in the
 scheduler

On Thu, Apr 16, 2015 at 08:24:27PM +0200, Ingo Molnar wrote:
> Yes ... but that still leaves this weird feeling that it's really 
> still a bit wrong because it's not proper parallel code, we just 
> reduced the probability of the remaining races radically. And it's not 
> like GCC (or any compiler) does load tearing or even store tearing 
> under normal -O2 for such code patterns, right?

I think Paul once caught GCC doing something silly, but typically no.
The re-loads however have been frequently observed.

> > And its not like they really cost anything.
> 
> That's true.
> 
> Would it make sense to add a few comments to the seq field definition 
> site(s), about how it's supposed to be accessed - or to the 
> READ_ONCE()/WRITE_ONCE() sites, to keep people from wondering?

For sure, can do a comment no problem.
--
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/