linux-kernel - Re: freezer: exec should clear PF_NOFREEZE along with PF

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Message-ID: <50C10391.4040903@canonical.com>
Date:	Thu, 06 Dec 2012 15:44:01 -0500
From:	Joseph Salisbury <joseph.salisbury@...onical.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Ben Hutchings <ben@...adent.org.uk>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Herton Krzesinski <herton.krzesinski@...onical.com>,
	linux-kernel@...r.kernel.org
Subject: Re: freezer: exec should clear PF_NOFREEZE along with PF_KTHREAD

On 12/06/2012 07:42 AM, Oleg Nesterov wrote:
> Hi,
>
> (add lkml)
>
> On 12/06, Ben Hutchings wrote:
>> On Wed, 2012-12-05 at 14:13 -0500, Joseph Salisbury wrote:
>>
>>> Hi Oleg,
>>>
>>> A bug was opened against the Ubuntu kernel[0].  It was found that
>>> reverting commit b40a79591ca918e7b91b0d9b6abd5d00f2e88c19 resolved this
>>> bug, and allowed suspend/resume to work properly.
>>>
>>> I see that you are the author of this patch, so I wanted to run it by
>>> you.  I was thinking of requesting a revert for 3.2 stable, but I wanted
>>> to get your feedback first.
>>>
>>> Thanks,
>>>
>>> Joe
>>>
>>>
>>> [0] https://bugs.launchpad.net/ubuntu/+source/v86d/+bug/1080530
>> If I understand this rightly:
>> 1. Suspend is aborted because the v86d usermodehelper cannot be frozen.
>> 2. Before this fix, usermodehelpers could inherit PF_NOFREEZE (what
>> could possibly go wrong with that?!), which is why this didn't
>> previously happen.
> Yes, try_to_freeze_tasks() ignores PF_NOFREEZE tasks
>
>> 3. However, usermodehelpers are supposed to be disabled while the
>> freezer is running.  Why is this one still running?
> __usermodehelper_disable() doesn't try to kill/stop/whatever the already
> spawned tasks...
>
> The question is, why v86d refuses to freeze? It sleeps in TASK_INTERRUPTIBLE.
>
>
> Oh... I seem to understand. This is 3.2 kernel, it also has PF_FREEZER_NOSIG.
> which should be cleared along with PF_NOFREEZE.
>
> This flag was removed upstream, but the older kernel need the fix. Could
> you test the patch below?
>
> Oleg.
>
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1084,7 +1084,7 @@ int flush_old_exec(struct linux_binprm *
>   
>   	set_fs(USER_DS);
>   	current->flags &=
> -		~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD | PF_NOFREEZE);
> +		~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD | PF_NOFREEZE | PF_FREEZER_NOSIG);
>   	flush_thread();
>   	current->personality &= ~bprm->per_clear;
>   
>

Hi Oleg,

A couple of people have tested your patch and report if fixes the 
suspend/resume bug[0].  Thanks for the quick fix!  Will you be 
requesting this patch in the stable kernels?

Thanks again,

Joe


[0] https://bugs.launchpad.net/bugs/1080530
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