From patchwork Tue Feb 13 13:22:57 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Will Deacon X-Patchwork-Id: 128232 Delivered-To: patch@linaro.org Received: by 10.46.124.24 with SMTP id x24csp4249503ljc; Tue, 13 Feb 2018 05:23:04 -0800 (PST) X-Google-Smtp-Source: AH8x227GWBwp07U5PP66+1exPRwFxMx0jxZ/Fu5IHzy+3EBxDmMjlX3HZMbJQeF+q0XR/ehmZDrT X-Received: by 10.99.43.73 with SMTP id r70mr1034371pgr.316.1518528184524; Tue, 13 Feb 2018 05:23:04 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1518528184; cv=none; d=google.com; s=arc-20160816; b=uzdlcWIalgdRyTf2c2KE2U4cfzPql011Iyy80vmA8Pc0m4tgvexmDX5U5QmKgTdE0I s4kFADebDLSSeA8ZLWLNQ3ufgZjNCWyb8gxb/BWDOyOJYyRCHSJVFgUv81wdZ/1/RAys VK8xxa1ckbfUJUUySU6x1COAhRDYmCw4YgPQkpO/BKUE05Tbr8tSPPcaBcSA2tTP6JgN aDwsH+SSBgVyJ7COPZPo/2RlCLj71b8BwzsNWjMaBD3lmrT/HYCpRQGmo5HXFXr08uA0 O3FsFGaGCvsPKNuR8B1xbzaMezM+OmEfi4Q/c28AuRrtp61wxFmjHRUf/y7DhlgHD8Bm UDSA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:references:in-reply-to:message-id:date :subject:cc:to:from:arc-authentication-results; bh=sAHxaFj77Cfd93EzPNsc2iU/IqHSi6NswFyevHAaYdQ=; b=cyCMigIiFvT6dJrSOt2FUWV97d4I35wnu4RS3s5ezgrA8VVc/WvcCMKyECdEtUnO8H FH4W9qHHhxSyJKejlW0Lr4yl8xt2X15yZv5vVffOP+2P2b9wbXiaqAeDFitidoy5A52+ OeOt8EVbz55WXSxCNQm/o+IiVrwQglcjSmagchBAM6p+RlrSBy90EV1X5iGADivh7YuM 0djKoYw0FJ5OZoVUrqPEoidecAi16rdX2i63SOT5watLeS0//bD5PiBYF6F+OXx4s8hO x++phVT+iDnmlk8PU0OGSweur/3bHubZCawxJy9M5DTnN/gO/+wEVc4kPqNqWluvJA6Z pm5g== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id v12si1220501pfl.330.2018.02.13.05.23.04; Tue, 13 Feb 2018 05:23:04 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935385AbeBMNXB (ORCPT + 27 others); Tue, 13 Feb 2018 08:23:01 -0500 Received: from foss.arm.com ([217.140.101.70]:57574 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935174AbeBMNW5 (ORCPT ); Tue, 13 Feb 2018 08:22:57 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EF65815BF; Tue, 13 Feb 2018 05:22:56 -0800 (PST) Received: from edgewater-inn.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id BFFD03F774; Tue, 13 Feb 2018 05:22:56 -0800 (PST) Received: by edgewater-inn.cambridge.arm.com (Postfix, from userid 1000) id 63E7D1AE5431; Tue, 13 Feb 2018 13:23:03 +0000 (GMT) From: Will Deacon To: linux-kernel@vger.kernel.org Cc: peterz@infradead.org, mingo@redhat.com, Will Deacon Subject: [PATCH 2/2] locking/qspinlock: Ensure node->count is updated before initialising node Date: Tue, 13 Feb 2018 13:22:57 +0000 Message-Id: <1518528177-19169-3-git-send-email-will.deacon@arm.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1518528177-19169-1-git-send-email-will.deacon@arm.com> References: <1518528177-19169-1-git-send-email-will.deacon@arm.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When queuing on the qspinlock, the count field for the current CPU's head node is incremented. This needn't be atomic because locking in e.g. IRQ context is balanced and so an IRQ will return with node->count as it found it. However, the compiler could in theory reorder the initialisation of node[idx] before the increment of the head node->count, causing an IRQ to overwrite the initialised node and potentially corrupt the lock state. Avoid the potential for this harmful compiler reordering by placing a barrier() between the increment of the head node->count and the subsequent node initialisation. Cc: Peter Zijlstra Cc: Ingo Molnar Signed-off-by: Will Deacon --- kernel/locking/qspinlock.c | 8 ++++++++ 1 file changed, 8 insertions(+) -- 2.1.4 diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 348c8cec1042..d880296245c5 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -379,6 +379,14 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) tail = encode_tail(smp_processor_id(), idx); node += idx; + + /* + * Ensure that we increment the head node->count before initialising + * the actual node. If the compiler is kind enough to reorder these + * stores, then an IRQ could overwrite our assignments. + */ + barrier(); + node->locked = 0; node->next = NULL; pv_init_node(node);