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Subject: Re: [PATCH] usb: gadget: f_mass_storage: Disable eps during
 disconnect
To:     Alan Stern <stern@rowland.harvard.edu>
CC:     <balbi@kernel.org>, <gregkh@linuxfoundation.org>,
        <linux-usb@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        Wesley Cheng <wcheng@codeaurora.org>
References: <20211026004456.23054-1-quic_wcheng@quicinc.com>
 <20211026144140.GA1288435@rowland.harvard.edu>
From:   Wesley Cheng <quic_wcheng@quicinc.com>
Message-ID: <81fc3f6d-f747-736b-32db-aecbca77dd31@quicinc.com>
Date:   Tue, 26 Oct 2021 12:40:04 -0700
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Hi Alan,

On 10/26/2021 7:41 AM, Alan Stern wrote:
> On Mon, Oct 25, 2021 at 05:44:56PM -0700, Wesley Cheng wrote:
>> From: Wesley Cheng <wcheng@codeaurora.org>
>>
>> When receiving a disconnect event from the UDC, the mass storage
>> function driver currently runs the handle_exception() routine
>> asynchronously.  For UDCs that support runtime PM, there is a
>> possibility the UDC is already suspended by the time the
>> do_set_interface() is executed.  This can lead to HW register access
>> while the UDC is already suspended.
>>
>> Signed-off-by: Wesley Cheng <wcheng@codeaurora.org>
>> ---
>>  drivers/usb/gadget/function/f_mass_storage.c | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/drivers/usb/gadget/function/f_mass_storage.c b/drivers/usb/gadget/function/f_mass_storage.c
>> index 3cabf7692ee1..752439690fda 100644
>> --- a/drivers/usb/gadget/function/f_mass_storage.c
>> +++ b/drivers/usb/gadget/function/f_mass_storage.c
>> @@ -2342,6 +2342,16 @@ static void fsg_disable(struct usb_function *f)
>>  {
>>  	struct fsg_dev *fsg = fsg_from_func(f);
>>  
>> +	/* Disable the endpoints */
>> +	if (fsg->bulk_in_enabled) {
>> +		usb_ep_disable(fsg->bulk_in);
> 
> According to the kerneldoc, this routine must be called in process 
> context.
> 
>> +		fsg->bulk_in_enabled = 0;
>> +	}
>> +	if (fsg->bulk_out_enabled) {
>> +		usb_ep_disable(fsg->bulk_out);
>> +		fsg->bulk_out_enabled = 0;
>> +	}
>> +
>>  	__raise_exception(fsg->common, FSG_STATE_CONFIG_CHANGE, NULL);
>>  }
> 
> Looks like you'll have to find a different way to avoid the problem.  
> For example, if an exception is pending then you might prevent the 
> gadget from going into runtime suspend until the exception has been 
> handled.
> 
Thanks for the suggestion.  I noticed that a lot of other FDs currently
call usb_ep_disable() in the disable/disconnect path as well.  Actually,
f_mass_storage seems to be the only one that doesn't do so.  Maybe we
should change the kerneldoc :)

Thanks
Wesley Cheng