linux-kernel - Re: [PATCH] atmel: fix an error handle in mxt

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Date:	Fri, 15 May 2015 10:42:51 +0800
From:	Pan Xinhui <xinhuix.pan@...el.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
CC:	linux-kernel@...r.kernel.org, nick.dyer@...ev.co.uk,
	miletus@...omium.org, bleung@...omium.org, djkurtz@...omium.org,
	mnipxh@...il.com, yanmin_zhang@...ux.intel.com
Subject: Re: [PATCH] atmel: fix an error handle in mxt_probe

HI, Dmitry
	thanks for your reply :)

On 2015年05月14日 01:41, Dmitry Torokhov wrote:
> Hi,
>
> On Wed, Apr 22, 2015 at 06:46:58PM +0800, Pan Xinhui wrote:
>> mxt_probe() may fail at last step, and the queue_work scheduled by request_firmware_nowait
>> may run later and then access some data which is freed.
>> To handle this error, add one mutex_lock to cover such case. It may cause module load delay only when the probe fails.
>>
>> here is the detail.
>>
>> module load:                                                             worker_thread:
>> mxt_probe -> mxt_initialize -> request_firmware_nowait (schedule_work)
>>                     |
>>              sysfs_create_group (fails)                                    mxt_config_cb -> mxt_configure_objects (may access data freed)
>>                     |
>>              err_free_object: some cleanup work, like free(data).
>>
>> Signed-off-by: xinhuix.pan <xinhuix.pan@...el.com>
>> ---
>>   drivers/input/touchscreen/atmel_mxt_ts.c | 14 ++++++++++++++
>>   1 file changed, 14 insertions(+)
>>
>> diff --git a/drivers/input/touchscreen/atmel_mxt_ts.c b/drivers/input/touchscreen/atmel_mxt_ts.c
>> index 2875ddf..af057c0 100644
>> --- a/drivers/input/touchscreen/atmel_mxt_ts.c
>> +++ b/drivers/input/touchscreen/atmel_mxt_ts.c
>> @@ -1978,10 +1978,19 @@ err_free_mem:
>>   static int mxt_configure_objects(struct mxt_data *data,
>>   				 const struct firmware *cfg);
>> +static DEFINE_MUTEX(err_probe_lock);
>> +static int err_probe;
>
> While you are right that bad things will happen if we let
> request_firmware_nowait() run after driver fails to bind to the device
> using statics to indicate success or failure is not good idea since you
> may have several such devices in your unit. Also it still doe snot help
> if you decide to unbind the device quickly or unlock the module.
>
> I guess the best way is to signal a completion from callback and wait
> for it in error path and in remove().
>
> Thanks.
>

yes, statics is not good.
It's also a good point that do some work both in err patch and in_remove().

thanks for your nice advices. I will work out patch V2.

thanks

xinhui

>> +
>>   static void mxt_config_cb(const struct firmware *cfg, void *ctx)
>>   {
>> +	mutex_lock(&err_probe_lock);
>> +	if (err_probe) {
>> +		mutex_unlock(&err_probe_lock);
>> +		return;
>> +	}
>>   	mxt_configure_objects(ctx, cfg);
>>   	release_firmware(cfg);
>> +	mutex_unlock(&err_probe_lock);
>>   }
>>   static int mxt_initialize(struct mxt_data *data)
>> @@ -2423,6 +2432,8 @@ static int mxt_probe(struct i2c_client *client, const struct i2c_device_id *id)
>>   	const struct mxt_platform_data *pdata;
>>   	int error;
>> +	err_probe = 0;
>> +
>>   	pdata = dev_get_platdata(&client->dev);
>>   	if (!pdata) {
>>   		pdata = mxt_parse_dt(client);
>> @@ -2472,6 +2483,9 @@ static int mxt_probe(struct i2c_client *client, const struct i2c_device_id *id)
>>   	return 0;
>>   err_free_object:
>> +	mutex_lock(&err_probe_lock);
>> +	err_probe = -1;
>> +	mutex_unlock(&err_probe_lock);
>>   	mxt_free_input_device(data);
>>   	mxt_free_object_table(data);
>>   err_free_irq:
>> --
>> 1.9.1
>
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