linux-kernel - Re: [PATCH 1/2] PM / sleep: ensure deferred probe workqueue is finished in wait_for_device

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Message-ID: <561D4C98.9070002@ti.com>
Date:	Tue, 13 Oct 2015 21:25:28 +0300
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
	<linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
	Thierry Reding <thierry.reding@...il.com>
Subject: Re: [PATCH 1/2] PM / sleep: ensure deferred probe workqueue is
 finished in wait_for_device_probe

On 10/10/2015 12:16 AM, Rafael J. Wysocki wrote:
> On Friday, October 09, 2015 09:38:13 AM Grygorii Strashko wrote:
>> On 10/08/2015 03:53 PM, Alan Stern wrote:
>>> On Thu, 8 Oct 2015, Rafael J. Wysocki wrote:
>>>
>>>>> @@ -391,6 +391,10 @@ int driver_probe_done(void)
>>>>>     */
>>>>>    void wait_for_device_probe(void)
>>>>>    {
>>>>> +	/* wait for the deferred probe workqueue to finish */
>>>>> +	if (driver_deferred_probe_enable)
>>>>> +		flush_workqueue(deferred_wq);
>>>>> +
>>>>>    	/* wait for the known devices to complete their probing */
>>>>>    	wait_event(probe_waitqueue, atomic_read(&probe_count) == 0);
>>>>>    	async_synchronize_full();
>>>>
>>>> I'm not sure if this is sufficient.
>>>>
>>>> Something may be added to the workqueue right after you've flushed it and
>>>> then be reporobed after the wait_event() in theory.  Or am I missing anything?
>>>
>>> Maybe I'm missing part of this, but I think the point is to make sure
>>> that every probe which began or was queued before this function got
>>> called, has finished before the function returns.
>>>
>>> Thus, in the case at hand we want to defer all probes starting from
>>> some point in the system sleep transition.  Grygorii sets his
>>> defer_all_probes variable and then calls this function.  It waits for
>>> any probes that were initiated before the function call.  Any probe
>>> that was initiated after the function call (for example, the ones
>>> you're concerned about between the flush_workqueue and wait_event) will
>>> see that defer_all_probes is set and so will defer itself.
>>
>> Yes. It will work as expected with the next patch.
>> For all other case, where this API is used alone -
>> it will make things more safe, but there is no way to completely block
>> scheduling of new probes.
>
> Well, in that case why don't you make it part of the second patch after all
> instead of making a false impression of fixing a more general problem?
>

ok.


-- 
regards,
-grygorii
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