From mboxrd@z Thu Jan 1 00:00:00 1970 From: Colin Cross Subject: Re: 3.11-rc regression bisected: s2disk does not work (was Re: [PATCH v3 13/16] futex: use freezable blocking call) Date: Tue, 23 Jul 2013 11:29:57 -0700 Message-ID: References: <1367884221-20462-1-git-send-email-ccross@android.com> <1367884221-20462-14-git-send-email-ccross@android.com> <20130723010250.5a3465ec@xenia.leun.net> <20130723200854.2046296b@xenia.leun.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: lkml , Pavel Machek , "Rafael J. Wysocki" , Peter Zijlstra , Ingo Molnar , Andrew Morton , Mandeep Singh Baines , Oleg Nesterov , linux-nfs , Linux PM list , netdev , Linus Torvalds , Tejun Heo , Darren Hart , Thomas Gleixner , Randy Dunlap , Al Viro To: Michael Leun Return-path: Received: from mail-ob0-f182.google.com ([209.85.214.182]:63520 "EHLO mail-ob0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933660Ab3GWS36 (ORCPT ); Tue, 23 Jul 2013 14:29:58 -0400 Received: by mail-ob0-f182.google.com with SMTP id va7so10756250obc.41 for ; Tue, 23 Jul 2013 11:29:57 -0700 (PDT) In-Reply-To: <20130723200854.2046296b@xenia.leun.net> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, Jul 23, 2013 at 11:08 AM, Michael Leun wrote: > On Mon, 22 Jul 2013 16:55:58 -0700 > Colin Cross wrote: > >> On Mon, Jul 22, 2013 at 4:02 PM, Michael Leun >> wrote: >> > On Mon, 6 May 2013 16:50:18 -0700 >> > Colin Cross wrote: >> > >> >> Avoid waking up every thread sleeping in a futex_wait call during >> > [...] >> > >> > With 3.11-rc s2disk from suspend-utils stopped working: Frozen at >> > displaying 0% of saving image to disk. >> > >> > echo "1" >/sys/power/state still works. >> > >> > Bisecting yielded 88c8004fd3a5fdd2378069de86b90b21110d33a4, >> > reverting that from 3.11-rc2 makes s2disk working again. >> > >> >> I think the expanded use of the freezable_* helpers is exposing an >> existing bug in hibernation. The SNAPSHOT_FREEZE ioctl calls >> freeze_processes(), which sets the global system_freezing_cnt and >> pm_freezing. try_to_freeze_tasks then sends every process except >> current a signal which causes them all to end up in the refrigerator. >> The current task then returns back to userspace and continues its work >> to suspend to disk. If that task ever hits a call to try_to_freeze() >> in the kernel, it will see system_freezing_cnt and pm_freezing=true >> and freeze, and suspend to disk will hang forever. It could hit >> try_to_freeze() because of a signal delivered to the task, or from >> calling any syscall that uses a freezable_* helper like the one I >> added to sys_futex. >> >> I think the right solution is to add a flag to the freezing task that >> marks it unfreezable. I think PF_NOFREEZE would work, although it is >> normally used on kernel threads, can you see if the attached patch >> helps? > > That patch helps. > > BTW, the only machine I can reproduce this bug with is an i7-3630QM > notebook. Cannot reproduce on an Core Duo U1400 and cannot reproduce on > an i7 M 620. > > Are the sysreq backtraces still wanted? If so, any tip, how I could get > them saved? > > > -- > MfG, > > Michael Leun > Any chance that the failing machine has threads=y in the suspend.conf file? Rafael, it appears that swsusp's suspend.c spawns new threads after calling the SNAPSHOT_FREEZE ioctl. The PF_NOFREEZE (or the new flag) will get copied to those new threads, but nothing will clear the flag. Should I just assume that the userspace suspend code will kill those threads before continuing with suspend? Or maybe add a WARN_ON in the kernel if any threads besides current have the new flag set when the suspend ops that assume all of userspace is frozen are called?