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

[Wang, Jiada]

Hi Dmitry

On 2020/04/02 23:00, Dmitry Osipenko wrote:
> 02.04.2020 16:24, Dmitry Osipenko ÐÐÑÐÑ:
> > 02.04.2020 14:50, Wang, Jiada ÐÐÑÐÑ:
> > > 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.
> > > > >
> > > > >  ÂÂÂÂ ThreadÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ Thread 2:
> > > > > =========================
> > > > > =========================
> > > > > mxt_update_fw_store()ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ mxt_remove()
> > > > > mutex_lock(&data->lock)ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ ...
> > > > > mxt_initialize()ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ //Tries to acquire lock
> > > > >  ÂÂ request_firmware_nowait()ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ mutex_lock(&data->lock)
> > > > > ...ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ ==>waits for lock()
> > > > > ...ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ .
> > > > > ...ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ .
> > > > > mutex_unlock(&data->lock)ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ .
> > > > >  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ //Gets lock and
> > > > > proceeds
> > > > >                                                  
> > > > > mxt_free_input_device();
> > > > >  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ ...
> > > > >                                                  
> > > > > mutex_unlock(&data->lock)
> > > > >  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ //Frees atmel driver
> > > > > data
> > > > >  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ 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.
> >
> > I'm actually now thinking that the suggestion about the module-count
> > wasn't very correct because this won't really help in regards to
> > mxt_update_fw_store() / mxt_remove() racing.
> >
> > I see that mxt_remove() already invokes the mxt_sysfs_remove(), which
> > should block until mxt_update_fw_store() is completed, shouldn't it?
> >
> > I guess the kfree(data) isn't the real cause of the problem and
> > something like this should help:
> >
> > diff --git a/drivers/input/touchscreen/atmel_mxt_ts.c
> > b/drivers/input/touchscreen/atmel_mxt_ts.c
> > index b2edf51e1595..4e66106feeb9 100644
> > --- a/drivers/input/touchscreen/atmel_mxt_ts.c
> > +++ b/drivers/input/touchscreen/atmel_mxt_ts.c
> > @@ -4254,6 +4254,7 @@ static void mxt_sysfs_remove(struct mxt_data *data)
> >   	struct i2c_client *client = data->client;
> >
> >   	sysfs_remove_group(&client->dev.kobj, &mxt_attr_group);
> > +	sysfs_remove_group(&client->dev.kobj, &mxt_fw_attr_group);
> >   }
> >
> >   static void mxt_reset_slots(struct mxt_data *data)
> > @@ -4649,31 +4650,19 @@ static int mxt_remove(struct i2c_client *client)
> >   {
> >   	struct mxt_data *data = i2c_get_clientdata(client);
> >
> > -	mutex_lock(&data->lock);
> > -	if (data->e_state == MXT_STATE_UPDATING_CONFIG_ASYNC ||
> > -	    data->e_state == MXT_STATE_UPDATING_CONFIG) {
> > -		data->e_state = MXT_STATE_GOING_AWAY;
> > -		mutex_unlock(&data->lock);
> > -		mxt_wait_for_completion(data, &data->update_cfg_completion,
> > -					MXT_CONFIG_TIMEOUT);
> > -	} else {
> > -		data->e_state = MXT_STATE_GOING_AWAY;
> > -		mutex_unlock(&data->lock);
> > -	}
> > +	mxt_sysfs_remove(data);
> >
> > -	disable_irq(data->irq);
> > -	sysfs_remove_group(&client->dev.kobj, &mxt_fw_attr_group);
> >   	if (data->reset_gpio) {
> >   		sysfs_remove_link(&client->dev.kobj, "reset");
> >   		gpiod_unexport(data->reset_gpio);
> >   	}
> > +
> >   	mxt_debug_msg_remove(data);
> > -	mxt_sysfs_remove(data);
> >   	mxt_free_input_device(data);
> >   	mxt_free_object_table(data);
> >
> > 	if (debug_state)
> > 		cancel_delayed_work_sync(&data->watchdog_work);
> > +	disable_irq(data->irq);
> >
> >   	return 0;
> >   }
>
> I'm looking at this again and the original tear-down order of the
> mxt_remove() looks okay, so no need to change it.
>
> Reading the commit message, it says that request_firmware_nowait() races
> with kfree(data), but that can't happen because the data is
> resource-managed and request_firmware_nowait() bumps device's use-count.
>
> https://elixir.bootlin.com/linux/v5.6.2/source/drivers/base/firmware_loader/main.c#L1043
>
> I think this patch was ported from some very old kernel version and it's
> simply not applicable to the upstream anymore.

I had some test,
and confirmed you are right,
this commit is no longer applicable to upstream,
but as discussed in another patch,
disable_irq() need to be moved after remove of mxt_fw_attr_group.
I will add this change in a new commit.

Thanks,
Jiada