linux-kernel - Re: [PATCH 2/9] staging: fsl-mc: fix device ref counting

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Date:   Fri, 3 Feb 2017 10:17:53 +0000
From:   Laurentiu Tudor <laurentiu.tudor@....com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "agraf@...e.de" <agraf@...e.de>, "arnd@...db.de" <arnd@...db.de>,
        "Ioana Ciornei" <ioana.ciornei@....com>,
        Ruxandra Ioana Radulescu <ruxandra.radulescu@....com>,
        Bharat Bhushan <bharat.bhushan@....com>,
        "Stuart Yoder" <stuart.yoder@....com>,
        Catalin Horghidan <catalin.horghidan@....com>,
        Leo Li <leoyang.li@....com>, Roy Pledge <roy.pledge@....com>
Subject: Re: [PATCH 2/9] staging: fsl-mc: fix device ref counting

Hi Greg,

Thanks for having a look. Comment below.

On 02/03/2017 11:56 AM, Greg KH wrote:
> On Wed, Feb 01, 2017 at 05:43:22AM -0600, laurentiu.tudor@....com wrote:
>> From: Laurentiu Tudor <laurentiu.tudor@....com>
>>
>> Drop unneeded get_device() call at device creation
>> and, as per documentation, drop reference count
>> after using device_find_child() return.
>>
>> Signed-off-by: Laurentiu Tudor <laurentiu.tudor@....com>
>> ---
>>   drivers/staging/fsl-mc/bus/dprc-driver.c | 1 +
>>   drivers/staging/fsl-mc/bus/fsl-mc-bus.c  | 1 -
>>   2 files changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/staging/fsl-mc/bus/dprc-driver.c b/drivers/staging/fsl-mc/bus/dprc-driver.c
>> index 4e416d8..e4b0341 100644
>> --- a/drivers/staging/fsl-mc/bus/dprc-driver.c
>> +++ b/drivers/staging/fsl-mc/bus/dprc-driver.c
>> @@ -188,6 +188,7 @@ static void dprc_add_new_devices(struct fsl_mc_device *mc_bus_dev,
>>   		child_dev = fsl_mc_device_lookup(obj_desc, mc_bus_dev);
>>   		if (child_dev) {
>>   			check_plugged_state_change(child_dev, obj_desc);
>> +			put_device(&child_dev->dev);
>>   			continue;
>>   		}
>>
>> diff --git a/drivers/staging/fsl-mc/bus/fsl-mc-bus.c b/drivers/staging/fsl-mc/bus/fsl-mc-bus.c
>> index cc20dc4..7c6a43b 100644
>> --- a/drivers/staging/fsl-mc/bus/fsl-mc-bus.c
>> +++ b/drivers/staging/fsl-mc/bus/fsl-mc-bus.c
>> @@ -537,7 +537,6 @@ int fsl_mc_device_add(struct dprc_obj_desc *obj_desc,
>>   		goto error_cleanup_dev;
>>   	}
>>
>> -	(void)get_device(&mc_dev->dev);
>
> This implies that your device reference counting is totally wrong and
> messed up.  Does this fix anything?  Break anything?  It should do
> something different now...

It fixes the refcounting in the sense that I'm now seeing the error
that i think you were referring to in your previous reviews,
when we hot unplug a device:

"Device 'foo.N' does not have a release() function, it is broken and 
must be fixed."

See next patch that adds the required callback.

Regarding this particular get_device(), i have no clue why the
original author placed it here. I've looked over other bus 
implementations and didn't see something similar.

---
Best Regards, Laurentiu