Re: [PATCH] driver core: Ensure proper suspend/resume ordering
From: Grygorii Strashko
Date: Wed Sep 16 2015 - 09:38:46 EST
On 09/16/2015 04:28 AM, Rafael J. Wysocki wrote:
> On Tuesday, September 15, 2015 03:18:19 PM Alan Stern wrote:
>> On Tue, 15 Sep 2015, Thierry Reding wrote:
>>
>>>> There are a few things to watch out for. Since the dpm_list gets
>>>> modified during system sleep transitions, we would have to make sure
>>>> that nothing gets probed during those times. In principle, that's what
>>>> the "prepare" stage is meant for, but there's still a race. As long as
>>>> no other kernel thread (such as the deferred probing mechanism) tries
>>>> to probe a device once everything has been frozen, we should be okay.
>>>> But if not, there will be trouble -- after the ->prepare callback runs,
>>>> the device is no longer on the dpm_list and so we don't want this patch
>>>> to put it back on that list.
>>>
>>> Perhaps moving to the end of the list needs to be a little smarter. That
>>> is it could check whether the device has been prepared for suspension or
>>> not and only move when it hasn't?
>>
>> Maybe. But doesn't that mean it won't solve your problem completely?
>>
>>> Then again, shouldn't the core even prohibit new probes once the suspend
>>> has been triggered? Sounds like asking for a lot of trouble if it didn't
>>> ...
>>
>> The core prohibits new devices from being registered. It does not
>> prohibit probes of existing devices, because they currently do not
>> affect the dpm_list.
Seems I missed smth, but I can't find the place in Kernel that prohibits
creation of new devices during suspend.
Could someone point me on, please?
--
regards,
-grygorii
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