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,URIBL_BLOCKED,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 57C2CC43381 for ; Mon, 4 Mar 2019 08:33:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 243E7208E4 for ; Mon, 4 Mar 2019 08:33:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1551688427; bh=gdFtEdLxq4Z9yGDCxaUxdhWosRLpFvjUS4PA1IJgz38=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=RU5GG4FbKe6g5w6KNT8p6dMZ6zTIftCZ07H3cijSU/NA3AOt3lnCaBjE9V5DepaPn 703wtbwPtmlIsUAsfL0ymERfU7XzREzKEM25931y+bOJV+dqYYUqC9OVsrYaQriIOc 8wVGkVOcrrg9bhW6avtOI0MGNN6RzqY7f8zcC6tE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728186AbfCDIdp (ORCPT ); Mon, 4 Mar 2019 03:33:45 -0500 Received: from mail.kernel.org ([198.145.29.99]:38528 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727872AbfCDIdh (ORCPT ); Mon, 4 Mar 2019 03:33:37 -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 86C3C20823; Mon, 4 Mar 2019 08:33:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1551688417; bh=gdFtEdLxq4Z9yGDCxaUxdhWosRLpFvjUS4PA1IJgz38=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=CpamSAnjK1lgfojA+8n5DeoQ9kw26G0HijG29HNhpdsbh3nnZQJsnlhz5P/75lUeF S2Yp+3P4Y7o/h9QyY3jSxZJYdM5pXv/JrDquR+LxNw0LmuyEXBb0J3wZYq/h7gSQDB WsXros43YmsKTPfa+VF4RXTNjexPWlRYbDjHQvdo= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Xie Yongji , Zhang Yu , "Peter Zijlstra (Intel)" , Linus Torvalds , Thomas Gleixner , Ingo Molnar , Sasha Levin Subject: [PATCH 4.20 38/88] locking/rwsem: Fix (possible) missed wakeup Date: Mon, 4 Mar 2019 09:22:21 +0100 Message-Id: <20190304081632.089885970@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 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 09b180063ee11..50d9af615dc49 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