On 19-11-24 06:03 pm, 胡连勤 wrote:
> Hello Prashanth:
>
>>> Considering that in some extreme cases, when u_serial driver is
>>> accessed by multiple threads, Thread A is executing the open operation
>>> and calling the gs_open, Thread B is executing the disconnect
>>> operation and calling the gserial_disconnect function,The
>>> port->port_usb pointer will be set to NULL.
>>>
>> [...]
>>> ---
>>> drivers/usb/gadget/function/u_serial.c | 25 +++++++++++++++----------
>>> 1 file changed, 15 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/usb/gadget/function/u_serial.c
>>> b/drivers/usb/gadget/function/u_serial.c
>>> index 0a8c05b2746b..9ab2dbed60a8 100644
>>> --- a/drivers/usb/gadget/function/u_serial.c
>>> +++ b/drivers/usb/gadget/function/u_serial.c
>>> @@ -124,6 +124,7 @@ struct gs_port {
>>> struct kfifo port_write_buf;
>>> wait_queue_head_t drain_wait; /* wait while writes drain */
>>> bool write_busy;
>>> + bool read_busy;
>>> wait_queue_head_t close_wait;
>>> bool suspended; /* port suspended */
>>> bool start_delayed; /* delay start when
>> suspended */
>>> @@ -331,9 +332,11 @@ __acquires(&port->port_lock)
>>> /* drop lock while we call out; the controller driver
>>> * may need to call us back (e.g. for disconnect)
>>> */
>>> + port->read_busy = true;
>>> spin_unlock(&port->port_lock);
>>> status = usb_ep_queue(out, req, GFP_ATOMIC);
>>> spin_lock(&port->port_lock);
>>> + port->read_busy = false;
>>>
>>> if (status) {
>>> pr_debug("%s: %s %s err %d\n",
>>> @@ -1412,19 +1415,21 @@ void gserial_disconnect(struct gserial *gser)
>>> /* tell the TTY glue not to do I/O here any more */
>>> spin_lock(&port->port_lock);
>>>
>>> - gs_console_disconnect(port);
>>> + if (!port->read_busy) {
>> start_tx/rx rely on port->port_usb for queuing the requests, and if its not
>> null during disconnect, tx/rx would keep on queuing requests to UDC even
>> after disconnect (which is not ideal). Here in your case, after read_busy is set,
>> start_rx would queue something outside of spinlock, meanwhile disconnect
>> happens but port_usb is still valid (because read_busy is set) and start_rx
>> would break early. But start_tx could continue queuing into disconnected
>> UDC (if 'started' is non-zero, which could happen due to timing). Can't you try
>> something like this,
>>
>> --- a/drivers/usb/gadget/function/u_serial.c
>> +++ b/drivers/usb/gadget/function/u_serial.c
>> @@ -579,9 +579,12 @@ static int gs_start_io(struct gs_port *port)
>> * we didn't in gs_start_tx() */
>> tty_wakeup(port->port.tty);
>> } else {
>> - gs_free_requests(ep, head, &port->read_allocated);
>> - gs_free_requests(port->port_usb->in, &port->write_pool,
>> - &port->write_allocated);
>> + /* Free reqs only if we are still connected */
>> + if (port->port_usb) {
>> + gs_free_requests(ep, head, &port->read_allocated);
>> + gs_free_requests(port->port_usb->in,
>> &port->write_pool,
>> + &port->write_allocated);
>> + }
>> status = -EIO;
>> }
>>
>> This will skip freeing reqs (and your crash) if port_usb is null and freeing
>> would be taken care by disconnect callback.
>>
>>
> First of all, the patch you gave can solve the problem we are currently facing.
>
> When we first encountered this problem, we also thought about adding a null check operation to deal with it,
> but we saw that the entry of this function (gs_start_io) had a null check operation for port->port_usb, so I gave up
> the idea of null check during free_req (maybe I made a simple problem complicated),
> and thought about optimizing it from the software logic, so that the port->port_usb pointer is always valid before gs_start_io is executed.
>
If it solves the problem, i guess you can use the null pointer check as
I suggested and send a new patchset, the current one will introduce new
problems. Keep the issue analysis as it is in commit text since its
descriptive enough to understand the problem.
Regards,
Prashanth K
