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[209.132.180.67]) by mx.google.com with ESMTP id w18si3744851otl.54.2019.12.04.10.20.46; Wed, 04 Dec 2019 10:20:58 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=PtQUcBzb; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731179AbfLDSKC (ORCPT + 99 others); Wed, 4 Dec 2019 13:10:02 -0500 Received: from mail.kernel.org ([198.145.29.99]:36138 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731140AbfLDSJu (ORCPT ); Wed, 4 Dec 2019 13:09:50 -0500 Received: from localhost (unknown [217.68.49.72]) (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 529D420675; Wed, 4 Dec 2019 18:09:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1575482989; bh=LOLqvixBSxMP5KYAl65i7gSikQHjB3I3I8XCQBbPr3k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=PtQUcBzbg1WDwFwjIbNmrMqAxsNM5pD3vVvFwMAKJeiZqne55UAMP/Oh5xVONfWzH RVn29KqCj1Ns+poEBO+4LmLNkSWZs5ioVe9qkPj0fqmGI1tEGo2ysIkMOsc9x52GRj IufPNcQPNRw2818Un139k+9bRtEsByGl45jLStFI= 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 4.14 195/209] futex: Add mutex around futex exit Date: Wed, 4 Dec 2019 18:56:47 +0100 Message-Id: <20191204175336.909515067@linuxfoundation.org> X-Mailer: git-send-email 2.24.0 In-Reply-To: <20191204175321.609072813@linuxfoundation.org> References: <20191204175321.609072813@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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 @@ -68,6 +68,7 @@ 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 @@ -959,6 +959,7 @@ 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 @@ -3721,12 +3721,23 @@ 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 @@ -3749,6 +3760,11 @@ 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)