From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751338AbdAPPN1 (ORCPT ); Mon, 16 Jan 2017 10:13:27 -0500 Received: from merlin.infradead.org ([205.233.59.134]:39806 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750922AbdAPPNY (ORCPT ); Mon, 16 Jan 2017 10:13:24 -0500 Date: Mon, 16 Jan 2017 16:13:19 +0100 From: Peter Zijlstra To: Byungchul Park Cc: mingo@kernel.org, tglx@linutronix.de, walken@google.com, boqun.feng@gmail.com, kirill@shutemov.name, linux-kernel@vger.kernel.org, linux-mm@kvack.org, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, npiggin@gmail.com Subject: Re: [PATCH v4 07/15] lockdep: Implement crossrelease feature Message-ID: <20170116151319.GE3144@twins.programming.kicks-ass.net> References: <1481260331-360-1-git-send-email-byungchul.park@lge.com> <1481260331-360-8-git-send-email-byungchul.park@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1481260331-360-8-git-send-email-byungchul.park@lge.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 09, 2016 at 02:12:03PM +0900, Byungchul Park wrote: > + /* > + * We assign class_idx here redundantly even though following > + * memcpy will cover it, in order to ensure a rcu reader can > + * access the class_idx atomically without lock. > + * > + * Here we assume setting a word-sized variable is atomic. which one, where? > + */ > + xlock->hlock.class_idx = hlock->class_idx; > + gen_id = (unsigned int)atomic_inc_return(&cross_gen_id); > + WRITE_ONCE(xlock->gen_id, gen_id); > + memcpy(&xlock->hlock, hlock, sizeof(struct held_lock)); > + INIT_LIST_HEAD(&xlock->xlock_entry); > + list_add_tail_rcu(&xlock->xlock_entry, &xlocks_head);