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

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Message-ID: <c53637ef-8e5d-3243-7236-5da360021f21@gmail.com>
Date:   Wed, 1 Apr 2020 19:04:38 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Jiada Wang <jiada_wang@...tor.com>, nick@...anahar.org,
        dmitry.torokhov@...il.com, jikos@...nel.org,
        benjamin.tissoires@...hat.com, bsz@...ihalf.com
Cc:     linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        erosca@...adit-jv.com, Andrew_Gabbasov@...tor.com
Subject: Re: [PATCH v10 54/55] Input: atmel_mxt_ts: Implement synchronization
 during various operation

31.03.2020 13:50, Jiada Wang пишет:
> From: Sanjeev Chugh <sanjeev_chugh@...tor.com>
> 
> 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()?