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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 8D138C43141 for ; Wed, 27 Nov 2019 21:16:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 63C41216F4 for ; Wed, 27 Nov 2019 21:16:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574889386; bh=6YJ2FBK9tb3kSPNyi7xxpiQNAB3C6of8Uba7WeIBLGE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=HjLoSIan+Gzjkn5P5lHPK2cmcC5NnNhz/zOWKSRq2pD3dM+4BOi9RLDpZsmulZsxP FmimP39p3rxJhXCfH7TlkoBhz5XaaVxNuBTGf1fwGKV2mOqvaQoHxWPNQBLXOhVTVs tEXqvPVvaJ+anL08UvrwIEcTJ4kk0NWD3csKymp4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732593AbfK0VQ0 (ORCPT ); Wed, 27 Nov 2019 16:16:26 -0500 Received: from mail.kernel.org ([198.145.29.99]:47342 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732909AbfK0VOJ (ORCPT ); Wed, 27 Nov 2019 16:14:09 -0500 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 757CF21741; Wed, 27 Nov 2019 21:14:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574889248; bh=6YJ2FBK9tb3kSPNyi7xxpiQNAB3C6of8Uba7WeIBLGE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=URpbBYgIdzg/SuyMoDQk4eqRcnrmwp5P+duMGusJ+9/dFspOYk/FyhDMzZ98yhrU+ ECeU7KyXmDmltTYhbXsmDC0T+lqaKt5ZC7hS9qbfj6bbrHN/fW6/4LxhJgN1SPxZPU 2RPjNdEn/tvYp4C3Yyilve7thgg7RfomEZBwXQt0= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Thomas Gleixner , Ingo Molnar , "Peter Zijlstra (Intel)" Subject: [PATCH 5.4 44/66] futex: Add mutex around futex exit Date: Wed, 27 Nov 2019 21:32:39 +0100 Message-Id: <20191127202726.363383483@linuxfoundation.org> X-Mailer: git-send-email 2.24.0 In-Reply-To: <20191127202632.536277063@linuxfoundation.org> References: <20191127202632.536277063@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Thomas Gleixner commit 3f186d974826847a07bc7964d79ec4eded475ad9 upstream. The mutex will be used in subsequent changes to replace the busy looping of a waiter when the futex owner is currently executing the exit cleanup to prevent a potential live lock. Signed-off-by: Thomas Gleixner Reviewed-by: Ingo Molnar Acked-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20191106224556.845798895@linutronix.de Signed-off-by: Greg Kroah-Hartman --- include/linux/futex.h | 1 + include/linux/sched.h | 1 + kernel/futex.c | 16 ++++++++++++++++ 3 files changed, 18 insertions(+) --- a/include/linux/futex.h +++ b/include/linux/futex.h @@ -65,6 +65,7 @@ static inline void futex_init_task(struc INIT_LIST_HEAD(&tsk->pi_state_list); tsk->pi_state_cache = NULL; tsk->futex_state = FUTEX_STATE_OK; + mutex_init(&tsk->futex_exit_mutex); } void futex_exit_recursive(struct task_struct *tsk); --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1054,6 +1054,7 @@ struct task_struct { #endif struct list_head pi_state_list; struct futex_pi_state *pi_state_cache; + struct mutex futex_exit_mutex; unsigned int futex_state; #endif #ifdef CONFIG_PERF_EVENTS --- a/kernel/futex.c +++ b/kernel/futex.c @@ -3698,12 +3698,23 @@ static void futex_cleanup(struct task_st */ void futex_exit_recursive(struct task_struct *tsk) { + /* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */ + if (tsk->futex_state == FUTEX_STATE_EXITING) + mutex_unlock(&tsk->futex_exit_mutex); tsk->futex_state = FUTEX_STATE_DEAD; } static void futex_cleanup_begin(struct task_struct *tsk) { /* + * Prevent various race issues against a concurrent incoming waiter + * including live locks by forcing the waiter to block on + * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in + * attach_to_pi_owner(). + */ + mutex_lock(&tsk->futex_exit_mutex); + + /* * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock. * * This ensures that all subsequent checks of tsk->futex_state in @@ -3726,6 +3737,11 @@ static void futex_cleanup_end(struct tas * take another loop until it becomes visible. */ tsk->futex_state = state; + /* + * Drop the exit protection. This unblocks waiters which observed + * FUTEX_STATE_EXITING to reevaluate the state. + */ + mutex_unlock(&tsk->futex_exit_mutex); } void futex_exec_release(struct task_struct *tsk)