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=-9.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,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 3E2F1C43381 for ; Mon, 4 Mar 2019 08:33:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0DE7121019 for ; Mon, 4 Mar 2019 08:33:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1551688421; bh=CMgftVj3ePoIYYOaMMG6XimnqCAQrstGhY2UJUR04sY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=oARf49vkEZ6v3TPvFn5/z7s6wZUvlgDjUNj/T9i3pNPAZdILhg/L1HXh3aK2JtlXX LHdJD+nIAsSx1xu6GeHcBKE2T234ygc+sMP4cgIh5Gd9ILpW7dMmauHFwcVFdHS9Mp THiPYjusiixp2CMDnCj7Il1beyAlTHhjTroZFipg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727818AbfCDIdj (ORCPT ); Mon, 4 Mar 2019 03:33:39 -0500 Received: from mail.kernel.org ([198.145.29.99]:38408 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727860AbfCDIdf (ORCPT ); Mon, 4 Mar 2019 03:33:35 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.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 CD2EC208E4; Mon, 4 Mar 2019 08:33:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1551688414; bh=CMgftVj3ePoIYYOaMMG6XimnqCAQrstGhY2UJUR04sY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fcOVfx/TNG1WqLNBdl7Mjs7K/y3PPEbbS5Zj5CBhyDkRocoSzM8hGei3vVblhpqc/ WcJSGKcxCHlQU+7xzec6Xwk1pHvd80qflUH8V5pXw6KSe6RHeelVXRvGA31LVB1Nih 8apr4OoT2pdgcruSYsvQAurMcVDhSdj/IcKnWAYU= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Peter Zijlstra (Intel)" , Linus Torvalds , Thomas Gleixner , Ingo Molnar , Sasha Levin Subject: [PATCH 4.20 37/88] futex: Fix (possible) missed wakeup Date: Mon, 4 Mar 2019 09:22:20 +0100 Message-Id: <20190304081632.053257281@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190304081630.610632175@linuxfoundation.org> References: <20190304081630.610632175@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore 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 4.20-stable review patch. If anyone has any objections, please let me know. ------------------ [ Upstream commit b061c38bef43406df8e73c5be06cbfacad5ee6ad ] We must not rely on wake_q_add() to delay the wakeup; in particular commit: 1d0dcb3ad9d3 ("futex: Implement lockless wakeups") moved wake_q_add() before smp_store_release(&q->lock_ptr, NULL), which could result in futex_wait() waking before observing ->lock_ptr == NULL and going back to sleep again. Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: 1d0dcb3ad9d3 ("futex: Implement lockless wakeups") Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin --- kernel/futex.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index 4d1b7db04e105..48449897476d5 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1444,11 +1444,7 @@ static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q) if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n")) return; - /* - * Queue the task for later wakeup for after we've released - * the hb->lock. wake_q_add() grabs reference to p. - */ - wake_q_add(wake_q, p); + get_task_struct(p); __unqueue_futex(q); /* * The waiting task can free the futex_q as soon as q->lock_ptr = NULL @@ -1458,6 +1454,13 @@ static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q) * plist_del in __unqueue_futex(). */ smp_store_release(&q->lock_ptr, NULL); + + /* + * Queue the task for later wakeup for after we've released + * the hb->lock. wake_q_add() grabs reference to p. + */ + wake_q_add(wake_q, p); + put_task_struct(p); } /* -- 2.19.1