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,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 F06E6C433F5 for ; Mon, 6 Sep 2021 01:24:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D9A7A61050 for ; Mon, 6 Sep 2021 01:24:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240504AbhIFBZm (ORCPT ); Sun, 5 Sep 2021 21:25:42 -0400 Received: from mail.kernel.org ([198.145.29.99]:39130 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239933AbhIFBYH (ORCPT ); Sun, 5 Sep 2021 21:24:07 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 627E261050; Mon, 6 Sep 2021 01:21:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1630891315; bh=awkMFSxMCgFztQ1H6e9Os/EiJVcjRzIoHJ5ntvCINHw=; h=From:To:Cc:Subject:Date:From; b=ha7wSTN7WznSPMNdyXEEx+WlRxWk1MlUwnyDWnyaiBBx0lAQRkCcruuQYo9g8tDqX XSGjtiGAQ+L2qRB38wrCp+qc1ZacKmyVisIJVNpbare+caJJymyd/4egdTQZd6UdJ7 rwNU8jhQGuAu0HgzwVUIALgU7KpxZgOmW0gnpN/6k/xOZWFc2f9M4aWEqqtZnuiXp8 yFz8SfAtID/pEOXofFvqmOxyx+E0vvAcLmlkhUrl6jg2RTsMCemEBFoiOSfRYaTy2U x+4XLgjROfd2dFOafd9Mus92pwAPXYbSlp6QhTyYZ/gLy/BXSP5+OH1lQQdP8EDLtw DTN/1rRewElPQ== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Peter Zijlstra , Yanfei Xu , Waiman Long , Sasha Levin Subject: [PATCH AUTOSEL 5.10 01/39] locking/mutex: Fix HANDOFF condition Date: Sun, 5 Sep 2021 21:21:15 -0400 Message-Id: <20210906012153.929962-1-sashal@kernel.org> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Peter Zijlstra [ Upstream commit 048661a1f963e9517630f080687d48af79ed784c ] Yanfei reported that setting HANDOFF should not depend on recomputing @first, only on @first state. Which would then give: if (ww_ctx || !first) first = __mutex_waiter_is_first(lock, &waiter); if (first) __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF); But because 'ww_ctx || !first' is basically 'always' and the test for first is relatively cheap, omit that first branch entirely. Reported-by: Yanfei Xu Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Waiman Long Reviewed-by: Yanfei Xu Link: https://lore.kernel.org/r/20210630154114.896786297@infradead.org Signed-off-by: Sasha Levin --- kernel/locking/mutex.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 15ac7c4bb111..86061901636c 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -938,7 +938,6 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx) { struct mutex_waiter waiter; - bool first = false; struct ww_mutex *ww; int ret; @@ -1017,6 +1016,8 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, set_current_state(state); for (;;) { + bool first; + /* * Once we hold wait_lock, we're serialized against * mutex_unlock() handing the lock off to us, do a trylock @@ -1045,15 +1046,9 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, spin_unlock(&lock->wait_lock); schedule_preempt_disabled(); - /* - * ww_mutex needs to always recheck its position since its waiter - * list is not FIFO ordered. - */ - if (ww_ctx || !first) { - first = __mutex_waiter_is_first(lock, &waiter); - if (first) - __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF); - } + first = __mutex_waiter_is_first(lock, &waiter); + if (first) + __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF); set_current_state(state); /* -- 2.30.2