Re: [PATCH] usb: f_mass_storage: test whether thread is running before starting another

[Michal Nazarewicz]

> On Tue, 5 Apr 2016, Michal Nazarewicz wrote:
>> When binding the function to usb_configuration, check whether the thread
>> is running before starting another one.  Without that, when function
>> instance is added to multiple configurations, fsg_bing starts multiple
>> threads with all but the latest one being forgotten by the driver.  This
>> leads to obvious thread leaks, possible lockups when trying to halt the
>> machine and possible more issues.
>> 
>> This fixes issues with legacy/multi gadget as well as configfs gadgets
>> when mass_storage function is added to multiple configurations.
>> 
>> This change also simplifies API since the legacy gadgets no longer need
>> to worry about starting the thread by themselves (which was where bug
>> in legacy/multi was in the first place).
>> 
>> Â I have no example failure though.  Conclusion that legacy/multi has
>>   a bug is based purely on me reading the code.
>> 
>> Signed-off-by: Michal Nazarewicz <mina86@xxxxxxxxxx>

On Tue, Apr 05 2016, Alan Stern wrote:
> This doesn't address the problem I raised in a previous email.  
> Sharing one thread among several function instances in the same config
> will not work if one of them encounters an error.

Each usb_function_instance has its own fsg_common and its own thread.
This was true in the past and is true with this patch as well.

And unless Iâm missing something, sharing a thread among multiple
usb_functionâs does not prevent the driver from working correctly.

Having the thread run even when itâs not used may be considered wasteful
but thatâs an orthogonal issue to the configfs failure.

-- 
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