From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752547Ab3KAKGw (ORCPT ); Fri, 1 Nov 2013 06:06:52 -0400 Received: from mga11.intel.com ([192.55.52.93]:30167 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751380Ab3KAKGv (ORCPT ); Fri, 1 Nov 2013 06:06:51 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.93,616,1378882800"; d="scan'208";a="426370315" Date: Fri, 1 Nov 2013 18:07:07 +0800 From: Yuanhan Liu To: Michel Lespinasse Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, Ingo Molnar , Linus Torvalds , Andrew Morton , Rik van Riel , Yuanhan Liu Subject: Re: [PATCH 1/4] mm/rmap: per anon_vma lock Message-ID: <20131101100707.GB30123@yliu-dev.sh.intel.com> References: <1383292467-28922-1-git-send-email-yuanhan.liu@linux.intel.com> <1383292467-28922-2-git-send-email-yuanhan.liu@linux.intel.com> <20131101084329.GB19466@laptop.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 01, 2013 at 02:22:25AM -0700, Michel Lespinasse wrote: > On Fri, Nov 1, 2013 at 1:43 AM, Peter Zijlstra wrote: > > AFAICT this isn't correct at all. We used to protect the vma interval > > tree with the root lock, now we don't. All we've got left is the > > mmap_sem, but anon_vma chains can cross address-spaces and thus we're up > > some creek without no paddle. > > Yes, that was my first thought as well (though I wanted to double > check at first). > > I also want to point out that lately we've seen several changes sent > out that relax locking with no accompanying explanation of why the > relaxed locking would be safe. Please don't do that - having a lot of > performance data is worthless if you can't explain why the new locking > is safe. Agreed. > And I'm not asking to prove a negative ('lack of any possible > races') there, but at least in this case one could dig out why the > root anon vma locking was introduced and if they think that this > reason doesn't apply anymore, explain why... It was introduced by commit 2b575eb6(And, BTW, I'm sorry that this commit log about bb4aa39676f is wrong) commit 2b575eb64f7a9c701fb4bfdb12388ac547f6c2b6 Author: Peter Zijlstra Date: Tue May 24 17:12:11 2011 -0700 mm: convert anon_vma->lock to a mutex Straightforward conversion of anon_vma->lock to a mutex. Signed-off-by: Peter Zijlstra Acked-by: Hugh Dickins Reviewed-by: KOSAKI Motohiro Cc: Benjamin Herrenschmidt Cc: David Miller Cc: Martin Schwidefsky Cc: Russell King Cc: Paul Mundt Cc: Jeff Dike Cc: Richard Weinberger Cc: Tony Luck Cc: KAMEZAWA Hiroyuki Cc: Mel Gorman Cc: Nick Piggin Cc: Namhyung Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds As you can see, Peter didn't tell why before. Honestly speaking, that was my originaly concern as well. I tried to find some possible races; I guess I may miss something. Thanks. --yliu