linux-kernel - Re: [RFC PATCH] Bluetooth: btusb: Fix memory leak in play

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Date:   Wed, 12 Jul 2017 10:27:04 +0800
From:   jeffy <jeffy.chen@...k-chips.com>
To:     Oliver Neukum <oliver@...kum.org>,
        Marcel Holtmann <marcel@...tmann.org>
CC:     LKML <linux-kernel@...r.kernel.org>, xiyou.wangcong@...il.com,
        Brian Norris <briannorris@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        "Gustavo F. Padovan" <gustavo@...ovan.org>
Subject: Re: [RFC PATCH] Bluetooth: btusb: Fix memory leak in play_deferred

Hi Oliver,

Thanx for your comments, and sorry for reply late.

On 07/04/2017 07:38 PM, Oliver Neukum wrote:
> Am Freitag, den 23.06.2017, 11:46 +0800 schrieb jeffy:
>>
>>>> ---
>>>>
>>>> drivers/bluetooth/btusb.c | 3 ++-
>>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
>>>> index 278e811..b469f9b 100644
>>>> --- a/drivers/bluetooth/btusb.c
>>>> +++ b/drivers/bluetooth/btusb.c
>>>> @@ -3254,11 +3254,12 @@ static int btusb_suspend(struct usb_interface *intf, pm_message_t message)
>>>>
>>>> static void play_deferred(struct btusb_data *data)
>>>> {
>>>> +	struct hci_dev *hdev = data->hdev;
>>>> 	struct urb *urb;
>>>> 	int err;
>>>>
>>>> 	while ((urb = usb_get_from_anchor(&data->deferred))) {
>>>> -		err = usb_submit_urb(urb, GFP_ATOMIC);
>>>> +		err = submit_tx_urb(hdev, urb);
>
> If you do that you have to change submit_tx_urb() to be called under a
> spinlock.

sorry, why we need that? since submit_tx_urb is basically 
usb_anchor_urb/usb_submit_urb/usb_free_urb

>
>>>> 		if (err < 0)
>>>> 			break;
>>>
>>> so why not just fix the memory leak here and instead call submit_tx_urb. I am not sure that is actually the right approach. Why anchor this URB now to the TX anchor now? Is that actually safe?
>>>
>> the current flow is:
>>     submit_or_queue_tx_urb
>>       if (!suspending)
>>         submit_tx_urb
>>       else
>>         put into deferred anchor
>>         wake btusb
>>
>>     retry the deferred urbs in deferred anchor(using usb_submit_urb)
>> after resumed
>>
>> so i think there are 2 problems here:
>> 1/ error handling, compare submit_tx_urb to usb_submit_urb, it freed
>> urb->setup_packet when failed to submit
>
> In theory yes. If we ever put control URBs on the deferred anchor.
>
>> 2/ memory leak:
>> in usb_submit_urb, we ref that urb
>> in __usb_hcd_giveback_urb, we unanchor it, and then unref it.
>>
>> so i think the usb_submit_urb expected the urb not just be referenced,
>> but also anchored?
>
> It expects that in the sense that it reacts to anchorings, but they are
> not required.
>
>> or referenced, but the caller would unref it himself
>> later?
>
> The caller is responsible for its own references.
hmm, maybe unref it in the complete callback(btusb_tx_complete?), and if 
we do so, we may need to detect which urb came from here...
>
>> and for tx_anchor, we put urb in it, and kill them all during suspending
>> to prevent transfer. so i guess it would be safe to put deferred urb in
>> to it after resume too?
>> but i don't know much about usb/btusb, so i could be wrong all about that :)
>
> IIRC the reason for directly submitting them was the spinlock.
sorry, i'm not clear about this, could you help to explain more? do you 
mean txlock?

the current play_deferred is called under txlock locked, and 
submit_tx_urb not:

         spin_lock_irq(&data->txlock);
         play_deferred(data);
         clear_bit(BTUSB_SUSPENDING, &data->flags);
         spin_unlock_irq(&data->txlock);


         spin_unlock_irqrestore(&data->txlock, flags);

         if (!suspending)
                 return submit_tx_urb(hdev, urb);


>
> 	Regards
> 		Oliver
>
>
>
>