From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754112Ab1HSOQf (ORCPT ); Fri, 19 Aug 2011 10:16:35 -0400 Received: from mail-bw0-f46.google.com ([209.85.214.46]:39818 "EHLO mail-bw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753346Ab1HSOQd (ORCPT ); Fri, 19 Aug 2011 10:16:33 -0400 From: Tejun Heo To: rjw@sisk.pl, menage@google.com, linux-kernel@vger.kernel.org Cc: arnd@arndb.de, oleg@redhat.com, Tejun Heo Subject: [PATCH 01/16] freezer: fix current->state restoration race in refrigerator() Date: Fri, 19 Aug 2011 16:16:07 +0200 Message-Id: <1313763382-12341-2-git-send-email-tj@kernel.org> X-Mailer: git-send-email 1.7.6 In-Reply-To: <1313763382-12341-1-git-send-email-tj@kernel.org> References: <1313763382-12341-1-git-send-email-tj@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org refrigerator() saves current->state before entering frozen state and restores it before returning using __set_current_state(); however, this is racy, for example, please consider the following sequence. set_current_state(TASK_INTERRUPTIBLE); try_to_sleep(); if (kthread_should_stop()) break; schedule(); If kthread_stop() races with ->state restoration, the restoration can restore ->state to TASK_INTERRUPTIBLE after kthread_stop() sets it to TASK_RUNNING but kthread_should_stop() may still see zero ->should_stop because there's no memory barrier between restoring TASK_INTERRUPTIBLE and kthread_should_stop() test. This isn't restricted to kthread_should_stop(). current->state is often used in memory barrier based synchronization and silently restoring it w/o mb breaks them. Use set_current_state() instead. Signed-off-by: Tejun Heo --- kernel/freezer.c | 8 +++++++- 1 files changed, 7 insertions(+), 1 deletions(-) diff --git a/kernel/freezer.c b/kernel/freezer.c index 7b01de9..575f863 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -58,7 +58,13 @@ void refrigerator(void) current->flags &= ~PF_FREEZING; pr_debug("%s left refrigerator\n", current->comm); - __set_current_state(save); + + /* + * Restore saved task state before returning. The mb'd version + * needs to be used; otherwise, it might silently break + * synchronization which depends on ordered task state change. + */ + set_current_state(save); } EXPORT_SYMBOL(refrigerator); -- 1.7.6