From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756142Ab2BBUic (ORCPT ); Thu, 2 Feb 2012 15:38:32 -0500 Received: from e28smtp09.in.ibm.com ([122.248.162.9]:55086 "EHLO e28smtp09.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754257Ab2BBUi2 (ORCPT ); Thu, 2 Feb 2012 15:38:28 -0500 Message-ID: <4F2AF41F.3050304@linux.vnet.ibm.com> Date: Fri, 03 Feb 2012 02:07:51 +0530 From: "Srivatsa S. Bhat" User-Agent: Mozilla/5.0 (X11; Linux i686; rv:9.0) Gecko/20111222 Thunderbird/9.0 MIME-Version: 1.0 To: "Rafael J. Wysocki" CC: pavel@ucw.cz, len.brown@intel.com, tj@kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] PM/Hibernate: Thaw kernel threads in hibernation_snapshot() in error/test path References: <20120202003359.9930.9844.stgit@srivatsabhat.in.ibm.com> <201202022118.15863.rjw@sisk.pl> <4F2AEFB8.8060304@linux.vnet.ibm.com> <201202022133.40009.rjw@sisk.pl> In-Reply-To: <201202022133.40009.rjw@sisk.pl> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit x-cbid: 12020220-2674-0000-0000-00000335A21A Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/03/2012 02:03 AM, Rafael J. Wysocki wrote: > On Thursday, February 02, 2012, Srivatsa S. Bhat wrote: >> On 02/03/2012 01:48 AM, Rafael J. Wysocki wrote: >> >>> On Thursday, February 02, 2012, Srivatsa S. Bhat wrote: >>>> On 02/03/2012 12:41 AM, Rafael J. Wysocki wrote: >>>> >>>>> On Thursday, February 02, 2012, Srivatsa S. Bhat wrote: >>>>>> In the hibernation call path, the kernel threads are frozen inside >>>>>> hibernation_snapshot(). If we happen to encounter an error further down >>>>>> the road or if we are exiting early due to a successful freezer test, >>>>>> then thaw kernel threads before returning to the caller. >>>>>> >>>>>> Signed-off-by: Srivatsa S. Bhat >>>>>> --- >>>>>> >>>>>> kernel/power/hibernate.c | 6 ++++-- >>>>>> kernel/power/user.c | 8 ++------ >>>>>> 2 files changed, 6 insertions(+), 8 deletions(-) >>>>>> >>>>>> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c >>>>>> index a5d4cf0..c6dee73 100644 >>>>>> --- a/kernel/power/hibernate.c >>>>>> +++ b/kernel/power/hibernate.c >>>>>> @@ -343,13 +343,13 @@ int hibernation_snapshot(int platform_mode) >>>>>> * successful freezer test. >>>>>> */ >>>>>> freezer_test_done = true; >>>>>> - goto Cleanup; >>>>>> + goto Thaw; >>>>>> } >>>>>> >>>>>> error = dpm_prepare(PMSG_FREEZE); >>>>>> if (error) { >>>>>> dpm_complete(PMSG_RECOVER); >>>>>> - goto Cleanup; >>>>>> + goto Thaw; >>>>>> } >>>>>> >>>>>> suspend_console(); >>>>>> @@ -385,6 +385,8 @@ int hibernation_snapshot(int platform_mode) >>>>>> platform_end(platform_mode); >>>>>> return error; >>>>>> >>>>>> + Thaw: >>>>>> + thaw_kernel_threads(); >>>>> >>>>> Actaully, no. You have to do swsusp_free() before thawing, otherwise >>>>> some allocations made by the just thawed kernel threads may fail. >>>>> >>>> But then what about the case (in the existing code) when >>>> freeze_kernel_threads() fails? It would first thaw kernel threads (in >>>> fact it used to thaw even userspace tasks earlier!) before calling >>>> swsusp_free(). So, the existing code itself seems to be brittle, considering >>>> the point you raised. Right? >>> >>> Well, that's why freeze_kernel_threads() originally hadn't tried to thaw anything >>> and started to do that after one of the Tejun's commits (and I forgot about >>> this particular issue back then). >>> >>>>>> Cleanup: >>>>>> swsusp_free(); >>>>>> goto Close; >>>>>> diff --git a/kernel/power/user.c b/kernel/power/user.c >>>>>> index 3e10007..7bee91f 100644 >>>>>> --- a/kernel/power/user.c >>>>>> +++ b/kernel/power/user.c >>>>>> @@ -249,16 +249,12 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd, >>>>>> } >>>>>> pm_restore_gfp_mask(); >>>>>> error = hibernation_snapshot(data->platform_support); >>>>>> - if (error) { >>>>>> - thaw_kernel_threads(); >>>>>> - } else { >>>>>> + if (!error) { >>>>>> error = put_user(in_suspend, (int __user *)arg); >>>>>> if (!error && !freezer_test_done) >>>>>> data->ready = 1; >>>>>> - if (freezer_test_done) { >>>>>> + if (freezer_test_done) >>>>>> freezer_test_done = false; >>>>>> - thaw_kernel_threads(); >>>>>> - } >>>>>> } >>>>>> break; >>>>> >>>>> Overall, this seems to be a cleanup, or is it a bug fix? >>>>> >>>> >>>> This was intended as a cleanup only, not a bug fix. But now, (see my point >>>> above), I am beginning to feel that the existing code itself is not robust >>>> enough... >>> >>> Well, let's pretend that we think it is safe to thaw kernel threads before >>> freeing memory (actually, they are frozen after the preallocation, so it >>> really should be OK). >>> >> >> >> Yeah, even I had the same reasoning in mind when writing this patch. >> >> >>> So I think I'll apply your patch after all. >>> >> :-) > > However, this one should probably be regarded as a regression fix: > > http://marc.info/?l=linux-kernel&m=132813572708843&w=4 > > because thawing all processes before calling swsusp_free() is definitely not > a good idea. > Right, I agree. So we need to get this into stable as well then.. Do you want me to re-spin the patch with the commit message explicitly stating that this is a regression fix and so on or is the current patch good enough? Regards, Srivatsa S. Bhat