Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755013Ab0KZKug (ORCPT ); Fri, 26 Nov 2010 05:50:36 -0500 Received: from hera.kernel.org ([140.211.167.34]:42324 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754741Ab0KZKue (ORCPT ); Fri, 26 Nov 2010 05:50:34 -0500 From: Tejun Heo To: roland@redhat.com, oleg@redhat.com, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, "rjw@sisk.plpavel"@ucw.cz Cc: Tejun Heo , "Rafael J. Wysocki" Subject: [PATCH 02/14] freezer: fix a race during freezing of TASK_STOPPED tasks Date: Fri, 26 Nov 2010 11:49:17 +0100 Message-Id: <1290768569-16224-3-git-send-email-tj@kernel.org> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1290768569-16224-1-git-send-email-tj@kernel.org> References: <1290768569-16224-1-git-send-email-tj@kernel.org> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.3 (hera.kernel.org [127.0.0.1]); Fri, 26 Nov 2010 10:49:47 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2486 Lines: 66 After calling freeze_task(), try_to_freeze_tasks() see whether the task is stopped or traced and if so, considers it to be frozen; however, nothing guarantees that either the task being frozen sees TIF_FREEZE or the freezer sees TASK_STOPPED -> TASK_RUNNING transition. The task being frozen may wake up and not see TIF_FREEZE while the freezer fails to notice the transition and believes the task is still stopped. This patch fixes the race by making freeze_task() always go through fake_signal_wake_up() for applicable tasks. The function goes through the target task's scheduler lock and thus guarantees that either the target sees TIF_FREEZE or try_to_freeze_task() sees TASK_RUNNING. Signed-off-by: Tejun Heo Cc: Oleg Nesterov Cc: Rafael J. Wysocki --- kernel/freezer.c | 9 +++++++-- kernel/power/process.c | 6 ++++++ 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/kernel/freezer.c b/kernel/freezer.c index bd1d42b..66ecd2e 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -104,8 +104,13 @@ bool freeze_task(struct task_struct *p, bool sig_only) } if (should_send_signal(p)) { - if (!signal_pending(p)) - fake_signal_wake_up(p); + fake_signal_wake_up(p); + /* + * fake_signal_wake_up() goes through p's scheduler + * lock and guarantees that TASK_STOPPED/TRACED -> + * TASK_RUNNING transition can't race with task state + * testing in try_to_freeze_tasks(). + */ } else if (sig_only) { return false; } else { diff --git a/kernel/power/process.c b/kernel/power/process.c index e50b4c1..eb2c88a 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -64,6 +64,12 @@ static int try_to_freeze_tasks(bool sig_only) * perturb a task in TASK_STOPPED or TASK_TRACED. * It is "frozen enough". If the task does wake * up, it will immediately call try_to_freeze. + * + * Because freeze_task() goes through p's + * scheduler lock after setting TIF_FREEZE, it's + * guaranteed that either we see TASK_RUNNING or + * try_to_stop() after schedule() in ptrace/signal + * stop sees TIF_FREEZE. */ if (!task_is_stopped_or_traced(p) && !freezer_should_skip(p)) -- 1.7.1 -- 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/