linux-kernel - Re: [PATCH] PM/Hibernate: Thaw kernel threads in hibernation

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Date:	Fri, 03 Feb 2012 01:31:11 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	pavel@....cz, len.brown@...el.com, tj@...nel.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PM/Hibernate: Thaw kernel threads in hibernation_snapshot()
 in error/test path

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 <srivatsa.bhat@...ux.vnet.ibm.com>
>> ---
>>
>>  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?

>>   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...
 
Regards,
Srivatsa S. Bhat

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