From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Parsons Subject: [PATCH] apm-emulation: Fix mutex race condition Date: Tue, 3 May 2011 01:16:30 +0100 (BST) Message-ID: <49798.52726.qm@web29017.mail.ird.yahoo.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-pm-bounces@lists.linux-foundation.org Errors-To: linux-pm-bounces@lists.linux-foundation.org To: linux-pm@lists.linux-foundation.org List-Id: linux-pm@vger.kernel.org A process suspending the system (e.g. apm -s) locks apm_mutex at the start of apm_ioctl() and keeps it locked while calling pm_suspend(). A second process trying to ACK the suspend (e.g. apmd) may then block in apm_ioctl() trying to lock the same mutex. The first process tries to freeze processes, but the ACK process cannot be frozen because mutex_lock() is uninterruptible. Consequently pm_suspend() will ultimately fail in try_to_freeze_tasks(). This patch allows the ACK process to be frozen if it is blocked in apm_ioctl(). Signed-off-by: Paul Parsons --- --- clean-2.6.39-rc5/drivers/char/apm-emulation.c 2011-03-15 01:20:32.000000000 +0000 +++ linux-2.6.39-rc5/drivers/char/apm-emulation.c 2011-05-03 00:34:05.467660807 +0100 @@ -275,7 +275,8 @@ apm_ioctl(struct file *filp, u_int cmd, if (!as->suser || !as->writer) return -EPERM; - mutex_lock(&apm_mutex); + while (mutex_lock_interruptible(&apm_mutex) < 0) + try_to_freeze(); switch (cmd) { case APM_IOC_SUSPEND: mutex_lock(&state_lock);