Re: [PATCH] PM / sleep: fix unbalanced pm runtime disable in __device_suspend_late()

[Grygorii Strashko]

On 05/20/2016 03:18 PM, Rafael J. Wysocki wrote:
> On Thursday, May 19, 2016 08:11:34 PM Grygorii Strashko wrote:
>> On 05/19/2016 04:38 PM, Rafael J. Wysocki wrote:
>>> On Fri, May 13, 2016 at 8:03 PM, Grygorii Strashko
>>> <grygorii.strashko@xxxxxx> wrote:
>>>> The PM runtime will be left disabled for the device if its .suspend_late()
>>>> callback fails and async suspend is not allowed for this device. In
>>>> this case device will not be added in dpm_late_early_list and
>>>> dpm_resume_early() will ignore this device, as result PM runtime will
>>>> be disabled for it forever (side effect: after 8 subsequent failures
>>>> for the same device the PM runtime will be reenabled due to
>>>> disable_depth overflow).
>>>>
>>>> Hence, re-enable PM runtime in __device_suspend_late() if
>>>> .suspend_late() callback fails and async suspend is not allowed for
>>>> this device.
>>>>
>>>> Signed-off-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
>>>> ---
>>>>    drivers/base/power/main.c | 7 +++++--
>>>>    1 file changed, 5 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
>>>> index 6e7c3cc..9b266e5 100644
>>>> --- a/drivers/base/power/main.c
>>>> +++ b/drivers/base/power/main.c
>>>> @@ -1207,10 +1207,13 @@ static int __device_suspend_late(struct device *dev, pm_message_t state, bool as
>>>>           }
>>>>
>>>>           error = dpm_run_callback(callback, dev, state, info);
>>>> -       if (!error)
>>>> +       if (!error) {
>>>>                   dev->power.is_late_suspended = true;
>>>> -       else
>>>> +       } else {
>> 		Point [1]
>>>>                   async_error = error;
>>>> +               if (!is_async(dev))
>>>
>>> Why is the is_async() check necessary here?
>> 			
>> A: deviceX is suspended *async* and reached point [1], in this case:
>> - deviceX has been added in dpm_late_early_list already
>> - dpm_suspend_late() will detect async_error and call dpm_resume_early()
>> - dpm_resume_early() will call device_resume_early() for deviceX
>> - device_resume_early() will re-enable PM runtime
>> {
>> ...
>> 	if (!dev->power.is_late_suspended)
>> 		goto Out;
>>
>> 	...
>>   Out:
>> 	TRACE_RESUME(error);
>>
>> 	pm_runtime_enable(dev);
>> ^^^^^^^^^^^^
>> 	complete_all(&dev->power.completion);
>> 	return error;
>> }	
>> 	
>>
>> B: deviceX is suspended *sync* and reached point [1], in this case:
>> - deviceX has not been added in dpm_late_early_list yet
>> - dpm_suspend_late() will detect sync_error and call dpm_resume_early()
>> - dpm_resume_early() will ignore deviceX
>>
>> if i'll not check for !is_async(dev) then pm_runtime_enable(dev)
>> will be called twice for deviceX with this patch.
> 
> OK, thanks!
> 
> So to me, the problem is that we handle failures in that code inconsistently
> depending on whether or not async suspend/resume is enabled for the device.
> 
> I'd rather make it consistent than add extra checks to it, so the patch below
> is how I would fix this.
> 
> ---
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> Subject: [PATCH] PM / sleep: Handle failures in device_suspend_late() consistently
> 
> Grygorii Strashko reports:
> 
>   The PM runtime will be left disabled for the device if its
>   .suspend_late() callback fails and async suspend is not allowed
>   for this device. In this case device will not be added in
>   dpm_late_early_list and dpm_resume_early() will ignore this
>   device, as result PM runtime will be disabled for it forever
>   (side effect: after 8 subsequent failures for the same device
>   the PM runtime will be reenabled due to disable_depth overflow).
> 
> To fix this problem, add devices to dpm_late_early_list regardless
> of whether or not device_suspend_late() returns errors for them.
> 
> That will ensure failures in there to be handled consistently for
> all devices regardless of their async suspend/resume status.
> 
> Reported-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
>   drivers/base/power/main.c |    5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> Index: linux-pm/drivers/base/power/main.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/main.c
> +++ linux-pm/drivers/base/power/main.c
> @@ -1267,14 +1267,15 @@ int dpm_suspend_late(pm_message_t state)
>   		error = device_suspend_late(dev);
>   
>   		mutex_lock(&dpm_list_mtx);
> +		if (!list_empty(&dev->power.entry))
> +			list_move(&dev->power.entry, &dpm_late_early_list);
> +
>   		if (error) {
>   			pm_dev_err(dev, state, " late", error);
>   			dpm_save_failed_dev(dev_name(dev));
>   			put_device(dev);
>   			break;
>   		}
> -		if (!list_empty(&dev->power.entry))
> -			list_move(&dev->power.entry, &dpm_late_early_list);
>   		put_device(dev);
>   
>   		if (async_error)
> 

Yep, it works too.
Tested-by: Grygorii Strashko <grygorii.strashko@xxxxxx>

By the way, there is third option:)

+++ b/drivers/base/power/main.c
@@ -1211,8 +1211,7 @@ static int __device_suspend_late(struct device *dev, pm_message_t state, bool as
                dev->power.is_late_suspended = true;
        } else {
                async_error = error;
-               if (!is_async(dev))
-                       pm_runtime_enable(dev);
+               error = 0;
        }



-- 
regards,
-grygorii