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=-19.4 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, 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 A336DC07E9B for ; Mon, 12 Jul 2021 07:29:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9468061400 for ; Mon, 12 Jul 2021 07:29:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346931AbhGLHbP (ORCPT ); Mon, 12 Jul 2021 03:31:15 -0400 Received: from mail.kernel.org ([198.145.29.99]:39618 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242936AbhGLHEP (ORCPT ); Mon, 12 Jul 2021 03:04:15 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 4F4B461107; Mon, 12 Jul 2021 07:01:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1626073287; bh=Oy5be5t/1nI8ffgcw3IWyLLcAjSX2IFQuUsBDWkUY+E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=2uC0L5nyYioiWHragYkCEaA+uTVnGnhMqFNeqEU9hQQNPdEmWJ0qPS789hIAsffmh NSsrns99OyWgvVQzAhYLUtfitFrzV7/QTYrDav6dtYnBgi3TJFGy7lO+HzRggy3EOB iqD63iwRAeaoBhRTL7p0ZN1pa4q+n58gehg9N88g= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Johannes Berg , Boqun Feng , "Peter Zijlstra (Intel)" , Sasha Levin Subject: [PATCH 5.12 190/700] lockding/lockdep: Avoid to find wrong lock dep path in check_irq_usage() Date: Mon, 12 Jul 2021 08:04:33 +0200 Message-Id: <20210712060953.672063206@linuxfoundation.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210712060924.797321836@linuxfoundation.org> References: <20210712060924.797321836@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Boqun Feng [ Upstream commit 7b1f8c6179769af6ffa055e1169610b51d71edd5 ] In the step #3 of check_irq_usage(), we seach backwards to find a lock whose usage conflicts the usage of @target_entry1 on safe/unsafe. However, we should only keep the irq-unsafe usage of @target_entry1 into consideration, because it could be a case where a lock is hardirq-unsafe but soft-safe, and in check_irq_usage() we find it because its hardirq-unsafe could result into a hardirq-safe-unsafe deadlock, but currently since we don't filter out the other usage bits, so we may find a lock dependency path softirq-unsafe -> softirq-safe, which in fact doesn't cause a deadlock. And this may cause misleading lockdep splats. Fix this by only keeping LOCKF_ENABLED_IRQ_ALL bits when we try the backwards search. Reported-by: Johannes Berg Signed-off-by: Boqun Feng Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20210618170110.3699115-4-boqun.feng@gmail.com Signed-off-by: Sasha Levin --- kernel/locking/lockdep.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 03a9d9b96045..b56c3855756e 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -2772,8 +2772,18 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev, * Step 3: we found a bad match! Now retrieve a lock from the backward * list whose usage mask matches the exclusive usage mask from the * lock found on the forward list. + * + * Note, we should only keep the LOCKF_ENABLED_IRQ_ALL bits, considering + * the follow case: + * + * When trying to add A -> B to the graph, we find that there is a + * hardirq-safe L, that L -> ... -> A, and another hardirq-unsafe M, + * that B -> ... -> M. However M is **softirq-safe**, if we use exact + * invert bits of M's usage_mask, we will find another lock N that is + * **softirq-unsafe** and N -> ... -> A, however N -> .. -> M will not + * cause a inversion deadlock. */ - backward_mask = original_mask(target_entry1->class->usage_mask); + backward_mask = original_mask(target_entry1->class->usage_mask & LOCKF_ENABLED_IRQ_ALL); ret = find_usage_backwards(&this, backward_mask, &target_entry); if (bfs_error(ret)) { -- 2.30.2