From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f42.google.com (mail-wm0-f42.google.com [74.125.82.42]) by kanga.kvack.org (Postfix) with ESMTP id 3E47B6B0253 for ; Wed, 9 Mar 2016 05:31:51 -0500 (EST) Received: by mail-wm0-f42.google.com with SMTP id l68so171239631wml.0 for ; Wed, 09 Mar 2016 02:31:51 -0800 (PST) Received: from casper.infradead.org (casper.infradead.org. [2001:770:15f::2]) by mx.google.com with ESMTPS id w66si20448814wmd.51.2016.03.09.02.31.49 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 09 Mar 2016 02:31:50 -0800 (PST) Date: Wed, 9 Mar 2016 11:31:43 +0100 From: Peter Zijlstra Subject: Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Message-ID: <20160309103143.GF25010@twins.programming.kicks-ass.net> References: <1457447457-25878-1-git-send-email-vgupta@synopsys.com> <56DEF3D3.6080008@synopsys.com> <56DFC604.6070407@synopsys.com> <20160309101349.GJ6344@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160309101349.GJ6344@twins.programming.kicks-ass.net> Sender: owner-linux-mm@kvack.org List-ID: To: Vineet Gupta Cc: Christoph Lameter , linux-mm@kvack.org, Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Noam Camus , stable@vger.kernel.org, linux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-parisc@vger.kernel, "James E.J. Bottomley" , Helge Deller , "linux-arch@vger.kernel.org" On Wed, Mar 09, 2016 at 11:13:49AM +0100, Peter Zijlstra wrote: > --- > Subject: bitops: Do not default to __clear_bit() for __clear_bit_unlock() > > __clear_bit_unlock() is a special little snowflake. While it carries the > non-atomic '__' prefix, it is specifically documented to pair with > test_and_set_bit() and therefore should be 'somewhat' atomic. > > Therefore the generic implementation of __clear_bit_unlock() cannot use > the fully non-atomic __clear_bit() as a default. > > If an arch is able to do better; is must provide an implementation of > __clear_bit_unlock() itself. > FWIW, we could probably undo this if we unified all the spinlock based atomic ops implementations (there's a whole bunch doing essentially the same), and special cased __clear_bit_unlock() for that. Collapsing them is probably a good idea anyway, just a fair bit of non-trivial work to figure out all the differences and if they matter etc.. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org