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 A87F9C43381 for ; Fri, 15 Feb 2019 02:13:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7523621934 for ; Fri, 15 Feb 2019 02:13:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550196837; bh=RKe2LF/cx7YUbbjZh7706T4DJbR5muk4fNC42Gzrjnk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=F9okN9/+YLqbTkQvVBALTeL3hEBlDi9+QDbDEvInZBWJ/vTPLbkujbr4AA3RaSk7M X0YW5CWA52+7a7vkqEkLQPPfXhvsC/eRgZGLBAcc/cji3MvD/GCi49XC/hQNLBN/n9 gzMUoyjOwTpHRguKwX/QW5u/kc/5fS2UQ4LqB+FQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405015AbfBOCNz (ORCPT ); Thu, 14 Feb 2019 21:13:55 -0500 Received: from mail.kernel.org ([198.145.29.99]:53796 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404935AbfBOCNx (ORCPT ); Thu, 14 Feb 2019 21:13:53 -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 5D3842229F; Fri, 15 Feb 2019 02:13:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550196832; bh=RKe2LF/cx7YUbbjZh7706T4DJbR5muk4fNC42Gzrjnk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GtrNRqeayNPH8pOt2sIF+PNPeF3IJUIEhJ+8x9biuR1MkTR3syybP2NiH0m1FdNSI SuD1tt71hDjGQgVRDOMBOh6+bDEtPDMrOre5o11GgYU0L13Ml0ia/pdhFpMUuxkDPR KxIp7fWpMK4tfelgJy8fx/djmJ9IRZ686UdHTpZM= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Xie Yongji , Zhang Yu , Peter Zijlstra , Linus Torvalds , Thomas Gleixner , Ingo Molnar , Sasha Levin Subject: [PATCH AUTOSEL 4.14 21/40] locking/rwsem: Fix (possible) missed wakeup Date: Thu, 14 Feb 2019 21:12:54 -0500 Message-Id: <20190215021313.178476-21-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: Xie Yongji [ Upstream commit e158488be27b157802753a59b336142dc0eb0380 ] Because wake_q_add() can imply an immediate wakeup (cmpxchg failure case), we must not rely on the wakeup being delayed. However, commit: e38513905eea ("locking/rwsem: Rework zeroing reader waiter->task") relies on exactly that behaviour in that the wakeup must not happen until after we clear waiter->task. [ peterz: Added changelog. ] Signed-off-by: Xie Yongji Signed-off-by: Zhang Yu Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: e38513905eea ("locking/rwsem: Rework zeroing reader waiter->task") Link: https://lkml.kernel.org/r/1543495830-2644-1-git-send-email-xieyongji@baidu.com Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin --- kernel/locking/rwsem-xadd.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index a90336779375..c75017326c37 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -198,15 +198,22 @@ static void __rwsem_mark_wake(struct rw_semaphore *sem, woken++; tsk = waiter->task; - wake_q_add(wake_q, tsk); + get_task_struct(tsk); list_del(&waiter->list); /* - * Ensure that the last operation is setting the reader + * Ensure calling get_task_struct() before setting the reader * waiter to nil such that rwsem_down_read_failed() cannot * race with do_exit() by always holding a reference count * to the task to wakeup. */ smp_store_release(&waiter->task, NULL); + /* + * Ensure issuing the wakeup (either by us or someone else) + * after setting the reader waiter to nil. + */ + wake_q_add(wake_q, tsk); + /* wake_q_add() already take the task ref */ + put_task_struct(tsk); } adjustment = woken * RWSEM_ACTIVE_READ_BIAS - adjustment; -- 2.19.1