Re: [PATCH v10 54/55] Input: atmel_mxt_ts: Implement synchronization during various operation

[Wang, Jiada]

Hi Dmitry

On 2020/04/02 1:04, Dmitry Osipenko wrote:
> 31.03.2020 13:50, Jiada Wang ÐÐÑÐÑ:
> > From: Sanjeev Chugh <sanjeev_chugh@xxxxxxxxxx>
> >
> > There could be scope of race conditions when sysfs is being handled
> > and at the same time, device removal is occurring. For example,
> > we don't want the device removal to begin if the Atmel device
> > cfg update is going on or firmware update is going on. In such
> > cases, wait for device update to be completed before the removal
> > continues.
> >
> >      Thread                                          Thread 2:
> > =========================                       =========================
> > mxt_update_fw_store()                           mxt_remove()
> > mutex_lock(&data->lock)                         ...
> > mxt_initialize()                                //Tries to acquire lock
> >    request_firmware_nowait()                     mutex_lock(&data->lock)
> > ...                                             ==>waits for lock()
> > ...                                             .
> > ...                                             .
> > mutex_unlock(&data->lock)                       .
> >                                                  //Gets lock and proceeds
> >                                                  mxt_free_input_device();
> >                                                  ...
> >                                                  mutex_unlock(&data->lock)
> >                                                  //Frees atmel driver data
> >                                                  kfree(data)
> >
> > If the request_firmware_nowait() completes after the driver removal,
> > and callback is triggered. But kernel crashes since the module is
> > already removed.
> >
> > This commit adds state machine to serialize such scenarios.
>
> Won't it be easier to bump driver's module use-count by __module_get()
> while firmware is updating? Or remove sysfs during of mxt_remove()? >

thanks for your inspiration, I will replace state machine with module 
use-count.

Thanks,
Jiada