From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta7.messagelabs.com (mail6.bemta7.messagelabs.com [216.82.255.55]) by kanga.kvack.org (Postfix) with ESMTP id B1E436B002D for ; Mon, 21 Nov 2011 13:13:06 -0500 (EST) Received: from /spool/local by e28smtp02.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 21 Nov 2011 23:43:01 +0530 Received: from d28av02.in.ibm.com (d28av02.in.ibm.com [9.184.220.64]) by d28relay05.in.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id pALICuuF4505776 for ; Mon, 21 Nov 2011 23:42:57 +0530 Received: from d28av02.in.ibm.com (loopback [127.0.0.1]) by d28av02.in.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id pALICui9012857 for ; Tue, 22 Nov 2011 05:12:56 +1100 Message-ID: <4ECA94A6.90500@linux.vnet.ibm.com> Date: Mon, 21 Nov 2011 23:42:54 +0530 From: "Srivatsa S. Bhat" MIME-Version: 1.0 Subject: [PATCH v4] PM / Memory-hotplug: Avoid task freezing failures References: <20111117083042.11419.19871.stgit@srivatsabhat.in.ibm.com> <201111192257.19763.rjw@sisk.pl> <4EC8984E.30005@linux.vnet.ibm.com> <201111201124.17528.rjw@sisk.pl> <4EC9D557.9090008@linux.vnet.ibm.com> <20111121164006.GB15314@google.com> <4ECA84A8.5030005@linux.vnet.ibm.com> In-Reply-To: <4ECA84A8.5030005@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Tejun Heo Cc: "Rafael J. Wysocki" , pavel@ucw.cz, lenb@kernel.org, ak@linux.intel.com, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, linux-mm@kvack.org, Chen Gong The lock_system_sleep() function is used in the memory hotplug code at several places in order to implement mutual exclusion with hibernation. However, this function tries to acquire the 'pm_mutex' lock using mutex_lock() and hence blocks in TASK_UNINTERRUPTIBLE state if it doesn't get the lock. This would lead to task freezing failures and hence hibernation failure as a consequence, even though the hibernation call path successfully acquired the lock. But it is to be noted that, since this task tries to acquire pm_mutex, if it blocks due to this, we are *100% sure* that this task is not going to run as long as hibernation sequence is in progress, since hibernation releases 'pm_mutex' only at the very end, when everything is done. And this means, this task is going to be anyway blocked for much more longer than what the freezer intends to achieve; which means, freezing and thawing doesn't really make any difference to this task! So, to fix freezing failures, we just ask the freezer to skip freezing this task, since it is already "frozen enough". But instead of calling freezer_do_not_count() and freezer_count() as it is, we use only the relevant parts of those functions, because restrictions such as 'the task should be a userspace one' etc., might not be relevant in this scenario. v4: Redesigned the whole fix, to ask the freezer to skip freezing the task which is blocked trying to acquire 'pm_mutex' lock. v3: Tejun suggested avoiding busy-looping by adding an msleep() since it is not guaranteed that we will get frozen immediately. v2: Tejun pointed problems with using mutex_lock_interruptible() in a while loop, when signals not related to freezing are involved. So, replaced it with mutex_trylock(). Signed-off-by: Srivatsa S. Bhat --- include/linux/suspend.h | 4 ++++ 1 files changed, 4 insertions(+), 0 deletions(-) diff --git a/include/linux/suspend.h b/include/linux/suspend.h index 57a6924..1f7fff4 100644 --- a/include/linux/suspend.h +++ b/include/linux/suspend.h @@ -380,12 +380,16 @@ static inline void unlock_system_sleep(void) {} static inline void lock_system_sleep(void) { + /* simplified freezer_do_not_count() */ + current->flags |= PF_FREEZER_SKIP; mutex_lock(&pm_mutex); } static inline void unlock_system_sleep(void) { mutex_unlock(&pm_mutex); + /* simplified freezer_count() */ + current->flags &= ~PF_FREEZER_SKIP; } #endif -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org