From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 02CFAC28EBD for ; Sun, 9 Jun 2019 12:10:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AB2AA2070B for ; Sun, 9 Jun 2019 12:10:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="nRmn0YNw" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728388AbfFIMK5 (ORCPT ); Sun, 9 Jun 2019 08:10:57 -0400 Received: from mail-lj1-f196.google.com ([209.85.208.196]:37663 "EHLO mail-lj1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727362AbfFIMK5 (ORCPT ); Sun, 9 Jun 2019 08:10:57 -0400 Received: by mail-lj1-f196.google.com with SMTP id 131so5466208ljf.4 for ; Sun, 09 Jun 2019 05:10:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=MGnWlXcEZlsDllQ1p+dLiYMxOQG545jMz4NgSBC9Y94=; b=nRmn0YNw8W+QR/WXpFQLQvxWieu7tL/WNi0q3+UMLXv1nXW9gwzTkCv8SY1aRpJeat ilJLCQYmFDEiyA3lldq0wUtt9f85fPZGz+jdQ/hHsk01cnqc6AUXcRN1GNDaWLJV14jX ngoF5Y2eJ4ywcfSSrZxnYcfyh8zCFxI53rHruVBiZnb1KSQtkRgLJIGZ6DOctY72Hm8S 5TbducFcWoCXLn2GTEd21oqtCp0N4r2+WEB+zmjhox+Yi53x81DvSYRbVf4NWSZqbe/P 0aiDUGPE3KavdxykFJkQrksAtAEmmw5rxLRm30FYIRBidXHsQ1OR0t18qhaGuetsxAZY TQNg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=MGnWlXcEZlsDllQ1p+dLiYMxOQG545jMz4NgSBC9Y94=; b=drz2dYTJX/XoMr0xFxwQ2T21XmTnPlf6wqbQFpl7svaIhyrhq6brw1gjxnGMU7imgc HLThBODfAzH/Ibll7sGn4J90ge4BpeXVbQ1FHLz8SyrVb/y+oZjP9I2AtKiGMibw0SHk Rfrbh9HyXnufalQNhOZoJfETsKyScZobjqwsN7Cjykkum2GcyI6Lmrbf1kN5yGfqN8DI UqrwPFk2AbhgbfiyE9gKfsTmLhGPXodK0UHf4ywZX2hmeOVi+5qgnYuG7CLZABfhgZKc RYnsM51Nf3HHE21PBAW/Lo08wQoTqnABGD1ujizRS4xcGthMjAVIOE/BaEFwiQfeyzK7 iykw== X-Gm-Message-State: APjAAAVYRn4vJIozbzsB9JEOG+XTAytCppg4pGfOChda/J68PkX03eSn 0k/Wg+p0sFs/qlUS08+e9T4= X-Google-Smtp-Source: APXvYqyrmwbev/kM38jFwPiKr2yUx7kn6QEzpscG18zuD1wOeoyI47i1pIxOyWt6Uu8NLD0OnZFBrg== X-Received: by 2002:a2e:9692:: with SMTP id q18mr34382352lji.89.1560082255174; Sun, 09 Jun 2019 05:10:55 -0700 (PDT) Received: from esperanza ([176.120.239.149]) by smtp.gmail.com with ESMTPSA id t3sm1423097lfk.59.2019.06.09.05.10.53 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sun, 09 Jun 2019 05:10:54 -0700 (PDT) Date: Sun, 9 Jun 2019 15:10:52 +0300 From: Vladimir Davydov To: Roman Gushchin Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, Johannes Weiner , Shakeel Butt , Waiman Long Subject: Re: [PATCH v6 01/10] mm: add missing smp read barrier on getting memcg kmem_cache pointer Message-ID: <20190609121052.kge3w3hv3t5u5bb3@esperanza> References: <20190605024454.1393507-1-guro@fb.com> <20190605024454.1393507-2-guro@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190605024454.1393507-2-guro@fb.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 04, 2019 at 07:44:45PM -0700, Roman Gushchin wrote: > Johannes noticed that reading the memcg kmem_cache pointer in > cache_from_memcg_idx() is performed using READ_ONCE() macro, > which doesn't implement a SMP barrier, which is required > by the logic. > > Add a proper smp_rmb() to be paired with smp_wmb() in > memcg_create_kmem_cache(). > > The same applies to memcg_create_kmem_cache() itself, > which reads the same value without barriers and READ_ONCE(). > > Suggested-by: Johannes Weiner > Signed-off-by: Roman Gushchin > --- > mm/slab.h | 1 + > mm/slab_common.c | 3 ++- > 2 files changed, 3 insertions(+), 1 deletion(-) > > diff --git a/mm/slab.h b/mm/slab.h > index 739099af6cbb..1176b61bb8fc 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -260,6 +260,7 @@ cache_from_memcg_idx(struct kmem_cache *s, int idx) > * memcg_caches issues a write barrier to match this (see > * memcg_create_kmem_cache()). > */ > + smp_rmb(); > cachep = READ_ONCE(arr->entries[idx]); Hmm, we used to have lockless_dereference() here, but it was replaced with READ_ONCE some time ago. The commit message claims that READ_ONCE has an implicit read barrier in it. commit 506458efaf153c1ea480591c5602a5a3ba5a3b76 Author: Will Deacon Date: Tue Oct 24 11:22:48 2017 +0100 locking/barriers: Convert users of lockless_dereference() to READ_ONCE() READ_ONCE() now has an implicit smp_read_barrier_depends() call, so it can be used instead of lockless_dereference() without any change in semantics. Signed-off-by: Will Deacon Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1508840570-22169-4-git-send-email-will.deacon@arm.com Signed-off-by: Ingo Molnar commit 76ebbe78f7390aee075a7f3768af197ded1bdfbb Author: Will Deacon Date: Tue Oct 24 11:22:47 2017 +0100 locking/barriers: Add implicit smp_read_barrier_depends() to READ_ONCE() In preparation for the removal of lockless_dereference(), which is the same as READ_ONCE() on all architectures other than Alpha, add an implicit smp_read_barrier_depends() to READ_ONCE() so that it can be used to head dependency chains on all architectures. Signed-off-by: Will Deacon Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1508840570-22169-3-git-send-email-will.deacon@arm.com Signed-off-by: Ingo Molnar