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=-16.0 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 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 76991C43381 for ; Tue, 16 Mar 2021 15:33:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5395C650F6 for ; Tue, 16 Mar 2021 15:33:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237953AbhCPPcx (ORCPT ); Tue, 16 Mar 2021 11:32:53 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:30268 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237948AbhCPPcG (ORCPT ); Tue, 16 Mar 2021 11:32:06 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615908725; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:in-reply-to:in-reply-to:references:references; bh=5lg9c5Rv+OApLdaRlqwCByn2jVsrPFVsUvLb5FWI36k=; b=K7aDVNGrYx8IRmWb1++9yEzw0I2JF+DohOMjBqJX4qyTP/1ZNGBQURuLNBjDS7rCb32GDz ioZEMVbtAwaBSu68/5twFJhMxkzj+2Abuqipa8SNox9LHXCZZfJoH+HhiS5AEIXY3a5Ut9 27+2CNI3tyvISJkdbiRtqdhXpQ6aZNk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-242-fIiQkzqFMAiWKhVqnxO_9Q-1; Tue, 16 Mar 2021 11:32:02 -0400 X-MC-Unique: fIiQkzqFMAiWKhVqnxO_9Q-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 454B73E741; Tue, 16 Mar 2021 15:32:01 +0000 (UTC) Received: from llong.com (ovpn-117-133.rdu2.redhat.com [10.10.117.133]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2F6AA19706; Tue, 16 Mar 2021 15:32:00 +0000 (UTC) From: Waiman Long To: Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng , "Paul E. McKenney" , Davidlohr Bueso Cc: linux-kernel@vger.kernel.org, Juri Lelli , Waiman Long Subject: [PATCH 3/4] locking/ww_mutex: Treat ww_mutex_lock() like a trylock Date: Tue, 16 Mar 2021 11:31:18 -0400 Message-Id: <20210316153119.13802-4-longman@redhat.com> In-Reply-To: <20210316153119.13802-1-longman@redhat.com> References: <20210316153119.13802-1-longman@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It was found that running the ww_mutex_lock-torture test produced the following lockdep splat almost immediately: [ 103.892638] ====================================================== [ 103.892639] WARNING: possible circular locking dependency detected [ 103.892641] 5.12.0-rc3-debug+ #2 Tainted: G S W [ 103.892643] ------------------------------------------------------ [ 103.892643] lock_torture_wr/3234 is trying to acquire lock: [ 103.892646] ffffffffc0b35b10 (torture_ww_mutex_2.base){+.+.}-{3:3}, at: torture_ww_mutex_lock+0x316/0x720 [locktorture] [ 103.892660] [ 103.892660] but task is already holding lock: [ 103.892661] ffffffffc0b35cd0 (torture_ww_mutex_0.base){+.+.}-{3:3}, at: torture_ww_mutex_lock+0x3e2/0x720 [locktorture] [ 103.892669] [ 103.892669] which lock already depends on the new lock. [ 103.892669] [ 103.892670] [ 103.892670] the existing dependency chain (in reverse order) is: [ 103.892671] [ 103.892671] -> #2 (torture_ww_mutex_0.base){+.+.}-{3:3}: [ 103.892675] lock_acquire+0x1c5/0x830 [ 103.892682] __ww_mutex_lock.constprop.15+0x1d1/0x2e50 [ 103.892687] ww_mutex_lock+0x4b/0x180 [ 103.892690] torture_ww_mutex_lock+0x316/0x720 [locktorture] [ 103.892694] lock_torture_writer+0x142/0x3a0 [locktorture] [ 103.892698] kthread+0x35f/0x430 [ 103.892701] ret_from_fork+0x1f/0x30 [ 103.892706] [ 103.892706] -> #1 (torture_ww_mutex_1.base){+.+.}-{3:3}: [ 103.892709] lock_acquire+0x1c5/0x830 [ 103.892712] __ww_mutex_lock.constprop.15+0x1d1/0x2e50 [ 103.892715] ww_mutex_lock+0x4b/0x180 [ 103.892717] torture_ww_mutex_lock+0x316/0x720 [locktorture] [ 103.892721] lock_torture_writer+0x142/0x3a0 [locktorture] [ 103.892725] kthread+0x35f/0x430 [ 103.892727] ret_from_fork+0x1f/0x30 [ 103.892730] [ 103.892730] -> #0 (torture_ww_mutex_2.base){+.+.}-{3:3}: [ 103.892733] check_prevs_add+0x3fd/0x2470 [ 103.892736] __lock_acquire+0x2602/0x3100 [ 103.892738] lock_acquire+0x1c5/0x830 [ 103.892740] __ww_mutex_lock.constprop.15+0x1d1/0x2e50 [ 103.892743] ww_mutex_lock+0x4b/0x180 [ 103.892746] torture_ww_mutex_lock+0x316/0x720 [locktorture] [ 103.892749] lock_torture_writer+0x142/0x3a0 [locktorture] [ 103.892753] kthread+0x35f/0x430 [ 103.892755] ret_from_fork+0x1f/0x30 [ 103.892757] [ 103.892757] other info that might help us debug this: [ 103.892757] [ 103.892758] Chain exists of: [ 103.892758] torture_ww_mutex_2.base --> torture_ww_mutex_1.base --> torture_ww_mutex_0.base [ 103.892758] [ 103.892763] Possible unsafe locking scenario: [ 103.892763] [ 103.892764] CPU0 CPU1 [ 103.892765] ---- ---- [ 103.892765] lock(torture_ww_mutex_0.base); [ 103.892767] lock(torture_ww_mutex_1.base); [ 103.892770] lock(torture_ww_mutex_0.base); [ 103.892772] lock(torture_ww_mutex_2.base); [ 103.892774] [ 103.892774] *** DEADLOCK *** Since ww_mutex is supposed to be deadlock-proof if used properly, such deadlock scenario should not happen. To avoid this false positive splat, treat ww_mutex_lock() like a trylock(). After applying this patch, the locktorture test can run for a long time without triggering the circular locking dependency splat. Signed-off-by: Waiman Long --- kernel/locking/mutex.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 622ebdfcd083..bb89393cd3a2 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -946,7 +946,10 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, } preempt_disable(); - mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip); + /* + * Treat as trylock for ww_mutex. + */ + mutex_acquire_nest(&lock->dep_map, subclass, !!ww_ctx, nest_lock, ip); if (__mutex_trylock(lock) || mutex_optimistic_spin(lock, ww_ctx, NULL)) { -- 2.18.1