From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754390Ab2BBUaA (ORCPT ); Thu, 2 Feb 2012 15:30:00 -0500 Received: from ogre.sisk.pl ([217.79.144.158]:34617 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753823Ab2BBU36 (ORCPT ); Thu, 2 Feb 2012 15:29:58 -0500 From: "Rafael J. Wysocki" To: "Srivatsa S. Bhat" Subject: Re: [PATCH] PM/Hibernate: Thaw kernel threads in hibernation_snapshot() in error/test path Date: Thu, 2 Feb 2012 21:33:39 +0100 User-Agent: KMail/1.13.6 (Linux/3.3.0-rc2+; KDE/4.6.0; x86_64; ; ) Cc: pavel@ucw.cz, len.brown@intel.com, tj@kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20120202003359.9930.9844.stgit@srivatsabhat.in.ibm.com> <201202022118.15863.rjw@sisk.pl> <4F2AEFB8.8060304@linux.vnet.ibm.com> In-Reply-To: <4F2AEFB8.8060304@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <201202022133.40009.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Thanks, Rafael