From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752702AbZBCCEQ (ORCPT ); Mon, 2 Feb 2009 21:04:16 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751352AbZBCCEA (ORCPT ); Mon, 2 Feb 2009 21:04:00 -0500 Received: from rv-out-0506.google.com ([209.85.198.238]:30884 "EHLO rv-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750977AbZBCCD7 (ORCPT ); Mon, 2 Feb 2009 21:03:59 -0500 From: =?utf-8?q?Arve=20Hj=C3=B8nnev=C3=A5g?= To: linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org Cc: swetland@google.com, mm-commits@vger.kernel.org, =?utf-8?q?Arve=20Hj=C3=B8nnev=C3=A5g?= Subject: [PATCH] PM: Fix suspend_console/resume_console to use only one semaphore. Date: Mon, 2 Feb 2009 18:03:44 -0800 Message-Id: <1233626624-28569-1-git-send-email-arve@android.com> X-Mailer: git-send-email 1.6.1 In-Reply-To: <1233372459-6434-2-git-send-email-arve@android.com> References: <1233372459-6434-2-git-send-email-arve@android.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This fixes a race where a thread acquires the console while the console is suspended, and the console is resumed before this thread releases it. In this case, the secondary console semaphore would be left locked, and the primary semaphore would be released twice. This in turn would cause the console switch on suspend or resume to hang forever. Note that suspend_console does not actually lock the console for clients that use acquire_console_sem, it only locks it for clients that use try_acquire_console_sem. If we change suspend_console to fully lock the console, then the kernel may deadlock on suspend. One client of try_acquire_console_sem is acquire_console_semaphore_for_printk, which uses it to prevent printk from using the console while it is suspended. Signed-off-by: Arve Hjønnevåg --- kernel/printk.c | 15 +++++++++------ 1 files changed, 9 insertions(+), 6 deletions(-) diff --git a/kernel/printk.c b/kernel/printk.c index 69188f2..e3602d0 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -73,7 +73,6 @@ EXPORT_SYMBOL(oops_in_progress); * driver system. */ static DECLARE_MUTEX(console_sem); -static DECLARE_MUTEX(secondary_console_sem); struct console *console_drivers; EXPORT_SYMBOL_GPL(console_drivers); @@ -891,12 +890,14 @@ void suspend_console(void) printk("Suspending console(s) (use no_console_suspend to debug)\n"); acquire_console_sem(); console_suspended = 1; + up(&console_sem); } void resume_console(void) { if (!console_suspend_enabled) return; + down(&console_sem); console_suspended = 0; release_console_sem(); } @@ -912,11 +913,9 @@ void resume_console(void) void acquire_console_sem(void) { BUG_ON(in_interrupt()); - if (console_suspended) { - down(&secondary_console_sem); - return; - } down(&console_sem); + if (console_suspended) + return; console_locked = 1; console_may_schedule = 1; } @@ -926,6 +925,10 @@ int try_acquire_console_sem(void) { if (down_trylock(&console_sem)) return -1; + if (console_suspended) { + up(&console_sem); + return -1; + } console_locked = 1; console_may_schedule = 0; return 0; @@ -979,7 +982,7 @@ void release_console_sem(void) unsigned wake_klogd = 0; if (console_suspended) { - up(&secondary_console_sem); + up(&console_sem); return; } -- 1.6.1