linux-kernel - Re: [RFC patch 0/5] futex: Allow lockless empty check of hashbucket plist in futex

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: <20131126115628.GK10022@twins.programming.kicks-ass.net>
Date:	Tue, 26 Nov 2013 12:56:28 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Davidlohr Bueso <davidlohr@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Jason Low <jason.low2@...com>,
	Darren Hart <dvhart@...ux.intel.com>,
	Mike Galbraith <efault@....de>, Jeff Mahoney <jeffm@...e.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Scott Norton <scott.norton@...com>,
	Tom Vaden <tom.vaden@...com>,
	Aswin Chandramouleeswaran <aswin@...com>,
	Waiman Long <Waiman.Long@...com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC patch 0/5] futex: Allow lockless empty check of hashbucket
 plist in futex_wake()

On Tue, Nov 26, 2013 at 12:21:40PM +0100, Ingo Molnar wrote:
> I'm somewhat reluctant to chalk it up to a single mfence - maybe 
> timings/behavior changed in some substantial way?

Ah indeed! We also changed the case where an enqueueing futex sees the
uval change and bails. It is now far more expensive due to having to
both queue and unqueue, whereas before it wouldn't queue at all.

I suppose the idea was to offset that by not requiring locking on the
wake side.
--
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/