From patchwork Thu Apr 15 14:25:52 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Ali Saidi X-Patchwork-Id: 422450 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=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=ham 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 DE0F6C433ED for ; Thu, 15 Apr 2021 14:26:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ADCE8613BA for ; Thu, 15 Apr 2021 14:26:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233346AbhDOO0q (ORCPT ); Thu, 15 Apr 2021 10:26:46 -0400 Received: from smtp-fw-6001.amazon.com ([52.95.48.154]:8912 "EHLO smtp-fw-6001.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230056AbhDOO0p (ORCPT ); Thu, 15 Apr 2021 10:26:45 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1618496783; x=1650032783; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=IYYHQjQUEYAY07onLm8+SW69KoZR6LGzsTny098YXCM=; b=pkywBVSSCtzez1EwimJgHNgqqyUseCYCUr2FgrOofQdfsBYBpZUSHMZY J/0rss4MsxurG6wYT2euQxNcZNwY2GOHQftiy2epJ+3pCB38pU0yKlDJQ okTstUqtUdYQgkJR3crt7VSL8y5sgHpeEjjBVgWdYuJxj+K7Xic3vnokG Q=; X-IronPort-AV: E=Sophos;i="5.82,225,1613433600"; d="scan'208";a="107687805" Received: from iad12-co-svc-p1-lb1-vlan2.amazon.com (HELO email-inbound-relay-1e-303d0b0e.us-east-1.amazon.com) ([10.43.8.2]) by smtp-border-fw-out-6001.iad6.amazon.com with ESMTP; 15 Apr 2021 14:26:22 +0000 Received: from EX13MTAUWB001.ant.amazon.com (iad12-ws-svc-p26-lb9-vlan3.iad.amazon.com [10.40.163.38]) by email-inbound-relay-1e-303d0b0e.us-east-1.amazon.com (Postfix) with ESMTPS id C7BC0A1E7F; Thu, 15 Apr 2021 14:26:18 +0000 (UTC) Received: from EX13D02UWB002.ant.amazon.com (10.43.161.160) by EX13MTAUWB001.ant.amazon.com (10.43.161.207) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Thu, 15 Apr 2021 14:26:17 +0000 Received: from EX13MTAUWB001.ant.amazon.com (10.43.161.207) by EX13D02UWB002.ant.amazon.com (10.43.161.160) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Thu, 15 Apr 2021 14:26:17 +0000 Received: from dev-dsk-alisaidi-i31e-9f3421fe.us-east-1.amazon.com (10.200.138.153) by mail-relay.amazon.com (10.43.161.249) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Thu, 15 Apr 2021 14:26:17 +0000 Received: by dev-dsk-alisaidi-i31e-9f3421fe.us-east-1.amazon.com (Postfix, from userid 5131138) id 65A02228E4; Thu, 15 Apr 2021 14:26:17 +0000 (UTC) From: Ali Saidi To: CC: , , , , , Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , Boqun Feng Subject: [PATCH] locking/qrwlock: Fix ordering in queued_write_lock_slowpath Date: Thu, 15 Apr 2021 14:25:52 +0000 Message-ID: <20210415142552.30916-1-alisaidi@amazon.com> X-Mailer: git-send-email 2.24.4.AMZN MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org While this code is executed with the wait_lock held, a reader can acquire the lock without holding wait_lock. The writer side loops checking the value with the atomic_cond_read_acquire(), but only truly acquires the lock when the compare-and-exchange is completed successfully which isn’t ordered. The other atomic operations from this point are release-ordered and thus reads after the lock acquisition can be completed before the lock is truly acquired which violates the guarantees the lock should be making. Fixes: b519b56e378ee ("locking/qrwlock: Use atomic_cond_read_acquire() when spinning in qrwloc") Signed-off-by: Ali Saidi Cc: stable@vger.kernel.org Acked-by: Will Deacon --- kernel/locking/qrwlock.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c index 4786dd271b45..10770f6ac4d9 100644 --- a/kernel/locking/qrwlock.c +++ b/kernel/locking/qrwlock.c @@ -73,8 +73,8 @@ void queued_write_lock_slowpath(struct qrwlock *lock) /* When no more readers or writers, set the locked flag */ do { - atomic_cond_read_acquire(&lock->cnts, VAL == _QW_WAITING); - } while (atomic_cmpxchg_relaxed(&lock->cnts, _QW_WAITING, + atomic_cond_read_relaxed(&lock->cnts, VAL == _QW_WAITING); + } while (atomic_cmpxchg_acquire(&lock->cnts, _QW_WAITING, _QW_LOCKED) != _QW_WAITING); unlock: arch_spin_unlock(&lock->wait_lock);