Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933085AbaDHSNQ (ORCPT ); Tue, 8 Apr 2014 14:13:16 -0400 Received: from merlin.infradead.org ([205.233.59.134]:46359 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932275AbaDHSNP (ORCPT ); Tue, 8 Apr 2014 14:13:15 -0400 Date: Tue, 8 Apr 2014 20:13:05 +0200 From: Peter Zijlstra To: Linus Torvalds Cc: Jan Stancek , Linux Kernel Mailing List , Srikar Dronamraju , Davidlohr Bueso , Ingo Molnar , Larry Woodman Subject: Re: [PATCH] futex: avoid race between requeue and wake Message-ID: <20140408181305.GT10526@twins.programming.kicks-ass.net> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 08, 2014 at 10:33:55AM -0700, Linus Torvalds wrote: > Hmm. And let's think about that powerpc race, where "spin_is_locked()" > can be false when somebody is waiting to get the lock.. Right; so in the original discussion I never really got to why that is a problem. A pending waiter cannot modify the wait list, so either we see the current holder, or we see a stable list. So I had to hop on a plane while that discussion was happening and while I did briefly task to Davidlohr in Napa his explanation didn't stick in my jet-leg addled brain. Afterwards the discussion got lost in the pile of unread mail. I'll go re-read that discussion and look up this thread to see if things will start to make sense. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/