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=-13.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 A2EAEC64E7D for ; Tue, 17 Nov 2020 12:59:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6C6E22151B for ; Tue, 17 Nov 2020 12:59:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="mE1eJ6jN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728908AbgKQM7F (ORCPT ); Tue, 17 Nov 2020 07:59:05 -0500 Received: from mail.kernel.org ([198.145.29.99]:54824 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728696AbgKQM5j (ORCPT ); Tue, 17 Nov 2020 07:57:39 -0500 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AD35B2465E; Tue, 17 Nov 2020 12:57:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605617858; bh=7BDpM/U1QXTcbiuS9/tXGhu9pULRxRWqkXsYrCCU214=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=mE1eJ6jNdMNwsieVsaaccmnWRSCbhJjwJalLqkmR1XG7MAM1qZ6bv4cHugzhsaKmP Pq5grGL7dPsYwIgb70tsabNvRWsCT1UtWUB1ArncCOnLvi+lGF578Yg59Mb/XYGSVG iatx6ecVZscPt6pEIWFx+OvAhaV186+MdCTylW94= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Boqun Feng , Chris Wilson , Peter Zijlstra , Sasha Levin Subject: [PATCH AUTOSEL 5.4 08/11] lockdep: Avoid to modify chain keys in validate_chain() Date: Tue, 17 Nov 2020 07:57:22 -0500 Message-Id: <20201117125725.599833-8-sashal@kernel.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20201117125725.599833-1-sashal@kernel.org> References: <20201117125725.599833-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Boqun Feng [ Upstream commit d61fc96a37603384cd531622c1e89de1096b5123 ] Chris Wilson reported a problem spotted by check_chain_key(): a chain key got changed in validate_chain() because we modify the ->read in validate_chain() to skip checks for dependency adding, and ->read is taken into calculation for chain key since commit f611e8cf98ec ("lockdep: Take read/write status in consideration when generate chainkey"). Fix this by avoiding to modify ->read in validate_chain() based on two facts: a) since we now support recursive read lock detection, there is no need to skip checks for dependency adding for recursive readers, b) since we have a), there is only one case left (nest_lock) where we want to skip checks in validate_chain(), we simply remove the modification for ->read and rely on the return value of check_deadlock() to skip the dependency adding. Reported-by: Chris Wilson Signed-off-by: Boqun Feng Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20201102053743.450459-1-boqun.feng@gmail.com Signed-off-by: Sasha Levin --- kernel/locking/lockdep.c | 19 +++++++++---------- 1 file changed, 9 insertions(+), 10 deletions(-) diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index bca0f7f71cde4..7f29d9ae6fcfa 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -2382,7 +2382,9 @@ print_deadlock_bug(struct task_struct *curr, struct held_lock *prev, * (Note that this has to be done separately, because the graph cannot * detect such classes of deadlocks.) * - * Returns: 0 on deadlock detected, 1 on OK, 2 on recursive read + * Returns: 0 on deadlock detected, 1 on OK, 2 if another lock with the same + * lock class is held but nest_lock is also held, i.e. we rely on the + * nest_lock to avoid the deadlock. */ static int check_deadlock(struct task_struct *curr, struct held_lock *next) @@ -2405,7 +2407,7 @@ check_deadlock(struct task_struct *curr, struct held_lock *next) * lock class (i.e. read_lock(lock)+read_lock(lock)): */ if ((next->read == 2) && prev->read) - return 2; + continue; /* * We're holding the nest_lock, which serializes this lock's @@ -2961,16 +2963,13 @@ static int validate_chain(struct task_struct *curr, if (!ret) return 0; - /* - * Mark recursive read, as we jump over it when - * building dependencies (just like we jump over - * trylock entries): - */ - if (ret == 2) - hlock->read = 2; /* * Add dependency only if this lock is not the head - * of the chain, and if it's not a secondary read-lock: + * of the chain, and if the new lock introduces no more + * lock dependency (because we already hold a lock with the + * same lock class) nor deadlock (because the nest_lock + * serializes nesting locks), see the comments for + * check_deadlock(). */ if (!chain_head && ret != 2) { if (!check_prevs_add(curr, hlock)) -- 2.27.0