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=-20.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,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 71502C4321A for ; Wed, 17 Mar 2021 12:39:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 21C8864F4D for ; Wed, 17 Mar 2021 12:39:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230092AbhCQMik (ORCPT ); Wed, 17 Mar 2021 08:38:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59332 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229558AbhCQMiY (ORCPT ); Wed, 17 Mar 2021 08:38:24 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D9AFAC06174A; Wed, 17 Mar 2021 05:38:23 -0700 (PDT) Date: Wed, 17 Mar 2021 12:38:21 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1615984702; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=a/W+qyeFPqNdojrexRzVnuBGVmMU+XNSQLpYMplD4SY=; b=TkGZngR3KwkXHepTAVZrGWmFiofuH1PwlHpybLygL/cZIUacAepypB4aiwFQ2sUnLd+B+y ac59CnQfuy+t2r7xk1b38uKE625ey+v/gSZOVCVdhLTwDtSOwsvq0Rilo9KT+TU1XLW+jS d5aL1wsJ3elVXtJ6hzjOx3r96QEPtMNZFyYDDHHuj7gR1c2cV/YyKTDcdymXSNyFU7YH6d PZOIk/p7UOZCbH+ODipvDCGzEjNl0QqDw07Esvx5SZB6Kow9tds08YSkuFu2Bo3WNPLnLv 5bwvUCG5d0EEmgJBGG5Eb4gxeEs3bMRoZ1/FapPF2LXYNmyVgdD8vLqGA9c89Q== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1615984702; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=a/W+qyeFPqNdojrexRzVnuBGVmMU+XNSQLpYMplD4SY=; b=3vLfaQVyNNmAGqZCvHjKcwRp5J5Q4YoVpzH/78jYr2qahmvwpvLO25TZjiSuKVP6MW96VY rBSlGuJSGOpaFTBw== From: "tip-bot2 for Waiman Long" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: locking/urgent] locking/ww_mutex: Treat ww_mutex_lock() like a trylock Cc: Waiman Long , Ingo Molnar , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20210316153119.13802-4-longman@redhat.com> References: <20210316153119.13802-4-longman@redhat.com> MIME-Version: 1.0 Message-ID: <161598470197.398.8903908266426306140.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the locking/urgent branch of tip: Commit-ID: b058f2e4d0a70c060e21ed122b264e9649cad57f Gitweb: https://git.kernel.org/tip/b058f2e4d0a70c060e21ed122b264e9649cad57f Author: Waiman Long AuthorDate: Tue, 16 Mar 2021 11:31:18 -04:00 Committer: Ingo Molnar CommitterDate: Wed, 17 Mar 2021 09:56:46 +01:00 locking/ww_mutex: Treat ww_mutex_lock() like a trylock 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 Signed-off-by: Ingo Molnar Acked-by Davidlohr Bueso Link: https://lore.kernel.org/r/20210316153119.13802-4-longman@redhat.com --- 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 622ebdf..bb89393 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)) {