From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756048Ab2BBUTf (ORCPT ); Thu, 2 Feb 2012 15:19:35 -0500 Received: from e23smtp06.au.ibm.com ([202.81.31.148]:47418 "EHLO e23smtp06.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754290Ab2BBUTd (ORCPT ); Thu, 2 Feb 2012 15:19:33 -0500 Message-ID: <4F2AEFB8.8060304@linux.vnet.ibm.com> Date: Fri, 03 Feb 2012 01:49:04 +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> <201202022011.55493.rjw@sisk.pl> <4F2AEB87.70908@linux.vnet.ibm.com> <201202022118.15863.rjw@sisk.pl> In-Reply-To: <201202022118.15863.rjw@sisk.pl> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit x-cbid: 12020210-7014-0000-0000-00000083ADCA Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > :-) Regards, Srivatsa S. Bhat