Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755428AbaFCMLk (ORCPT ); Tue, 3 Jun 2014 08:11:40 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:43443 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932555AbaFCLlF (ORCPT ); Tue, 3 Jun 2014 07:41:05 -0400 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Lai Jiangshan , Tejun Heo , Luis Henriques Subject: [PATCH 3.11 048/138] workqueue: fix a possible race condition between rescuer and pwq-release Date: Tue, 3 Jun 2014 12:38:14 +0100 Message-Id: <1401795584-22664-49-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1401795584-22664-1-git-send-email-luis.henriques@canonical.com> References: <1401795584-22664-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.11.10.11 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Lai Jiangshan commit 77668c8b559e4fe2acf2a0749c7c83cde49a5025 upstream. There is a race condition between rescuer_thread() and pwq_unbound_release_workfn(). Even after a pwq is scheduled for rescue, the associated work items may be consumed by any worker. If all of them are consumed before the rescuer gets to them and the pwq's base ref was put due to attribute change, the pwq may be released while still being linked on @wq->maydays list making the rescuer dereference already freed pwq later. Make send_mayday() pin the target pwq until the rescuer is done with it. tj: Updated comment and patch description. Signed-off-by: Lai Jiangshan Signed-off-by: Tejun Heo Signed-off-by: Luis Henriques --- kernel/workqueue.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 2b48572be9b3..23071c9acdc1 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1894,6 +1894,12 @@ static void send_mayday(struct work_struct *work) /* mayday mayday mayday */ if (list_empty(&pwq->mayday_node)) { + /* + * If @pwq is for an unbound wq, its base ref may be put at + * any time due to an attribute change. Pin @pwq until the + * rescuer is done with it. + */ + get_pwq(pwq); list_add_tail(&pwq->mayday_node, &wq->maydays); wake_up_process(wq->rescuer->task); } @@ -2421,6 +2427,12 @@ repeat: process_scheduled_works(rescuer); /* + * Put the reference grabbed by send_mayday(). @pool won't + * go away while we're holding its lock. + */ + put_pwq(pwq); + + /* * Leave this pool. If keep_working() is %true, notify a * regular worker; otherwise, we end up with 0 concurrency * and stalling the execution. -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/