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=-9.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 2416FC43381 for ; Fri, 15 Feb 2019 02:26:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E969A20836 for ; Fri, 15 Feb 2019 02:26:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550197591; bh=OuND4bUQC/DN21xljX2lNIyCCxtPqZCcLou+dTA7xqQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=iCeeijLGBuB0QkhU33dMa+FAUshsHWQpzeqh+fWl3XkyVmwvUza04jB74wfzIqFwX ZKSc4rO5K6BLyAu4C3tNWoDTzsiD6Rqwc+zxkAEIzTgZRnn50T/ciYHkRm1k/AZqEv tHa2nQBw7QiQasQAXNB2ZGV9B8vKm805EmPhw7Pw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729797AbfBOC03 (ORCPT ); Thu, 14 Feb 2019 21:26:29 -0500 Received: from mail.kernel.org ([198.145.29.99]:53780 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404917AbfBOCNv (ORCPT ); Thu, 14 Feb 2019 21:13:51 -0500 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 29ED921B68; Fri, 15 Feb 2019 02:13:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550196831; bh=OuND4bUQC/DN21xljX2lNIyCCxtPqZCcLou+dTA7xqQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=yjzNU64VkRAd2/VGkLNKD9QUfWRim+G1uguFmmOSYqPNfBgmTm4CVmUjtoyCZkk3T v80auNKEMB96ZKgMHzO8L8Yw/xbg55gHGwN9Y8XOc11ZrvGWFo9ut8k6zj0Mi9HHEK c9XrKsmw80kqgQkqd8dai/P2upZaK9Y88bbmstwY= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Peter Zijlstra , Linus Torvalds , Thomas Gleixner , Ingo Molnar , Sasha Levin Subject: [PATCH AUTOSEL 4.14 20/40] futex: Fix (possible) missed wakeup Date: Thu, 14 Feb 2019 21:12:53 -0500 Message-Id: <20190215021313.178476-20-sashal@kernel.org> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20190215021313.178476-1-sashal@kernel.org> References: <20190215021313.178476-1-sashal@kernel.org> MIME-Version: 1.0 X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra [ 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 046cd780d057..176913206579 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1405,11 +1405,7 @@ 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 @@ -1419,6 +1415,13 @@ 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