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SubjectRe: [PATCH] coresight: use put_device() instead of kfree()
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On Tuesday 27 March 2018 03:16 AM, Mathieu Poirier wrote:
> drivers/hwtracing/coresight/coresight.c
> On 18 March 2018 at 01:38, Arvind Yadav <arvind.yadav.cs@gmail.com> wrote:
>> Never directly free @dev after calling device_register(), even
>> if it returned an error. Always use put_device() to give up the
>> reference initialized.
>>
>> Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
>> ---
>> drivers/hwtracing/coresight/coresight.c | 8 ++++----
>> 1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/hwtracing/coresight/coresight.c b/drivers/hwtracing/coresight/coresight.c
>> index 389c4ba..132dfbc 100644
>> --- a/drivers/hwtracing/coresight/coresight.c
>> +++ b/drivers/hwtracing/coresight/coresight.c
>> @@ -1026,8 +1026,10 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
>> dev_set_name(&csdev->dev, "%s", desc->pdata->name);
>>
>> ret = device_register(&csdev->dev);
>> - if (ret)
>> - goto err_device_register;
>> + if (ret) {
>> + put_device(&csdev->dev);
>> + goto err_kzalloc_csdev;
>> + }
>>
>> mutex_lock(&coresight_mutex);
>>
>> @@ -1038,8 +1040,6 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
>>
>> return csdev;
>>
>> -err_device_register:
>> - kfree(conns);
> Apologies for the late reply, I was travelling.
>
> I suggest to simply replace kfree() with put_device() in order to
> concentrate the error handling code in the same area and make sure
> that memory allocated for @conns and @refcnts is freed.
>
> Thanks,
> Mathieu

If you will see the comment for device_register(drivers/base/core.c)
there is mentioned that 'NOTE: _Never_ directly free @dev
after calling this function, even if it returned an error!
Always use put_device() to give up the reference initialized
in this function instead.
Here put_device() will decrement the last reference and then
free the memory by calling dev->release. Internally
put_device() -> kobject_put() -> kobject_cleanup() which is
responsible to call 'dev -> release' and also free other kobject
resources. we should always avoid kfree() if device_register()
returned an error. Otherwise it'll not do clean up of other
kobject resources.

~arvind
>> err_kzalloc_conns:
>> kfree(refcnts);
>> err_kzalloc_refcnts:
>> --
>> 2.7.4
>>

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