linux-kernel - Re: [PATCH v2 02/16] bus: mhi: core: Add support for registering MHI controllers

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Date:   Thu, 13 Feb 2020 20:52:55 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     arnd@...db.de, smohanad@...eaurora.org, jhugo@...eaurora.org,
        kvalo@...eaurora.org, bjorn.andersson@...aro.org,
        hemantk@...eaurora.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 02/16] bus: mhi: core: Add support for registering MHI
 controllers

Hi Greg,

On Tue, Feb 11, 2020 at 11:22:36AM -0800, Greg KH wrote:
> On Wed, Feb 12, 2020 at 12:41:47AM +0530, Manivannan Sadhasivam wrote:
> > Hi Greg,
> > 
> > On Thu, Feb 06, 2020 at 05:56:06PM +0100, Greg KH wrote:
> > > On Fri, Jan 31, 2020 at 07:19:55PM +0530, Manivannan Sadhasivam wrote:
> > > > +static void mhi_release_device(struct device *dev)
> > > > +{
> > > > +	struct mhi_device *mhi_dev = to_mhi_device(dev);
> > > > +
> > > > +	if (mhi_dev->ul_chan)
> > > > +		mhi_dev->ul_chan->mhi_dev = NULL;
> > > 
> > > That looks really odd.  Why didn't you just drop the reference you
> > > should have grabbed here for this pointer?  You did properly increment
> > > it when you saved it, right?  :)
> > > 
> > 
> > Well, there is no reference count (kref) exist for mhi_dev.
> 
> Then something is wrong with your model :(
> 
> You can't save pointers off to things without reference counting, that
> is going to cause you real problems.  See the coding style document for
> all the details.
> 
> > And we really needed to NULL the mhi_dev to avoid any dangling
> > reference to it.
> 
> Again, that's not how to do this correctly.
> 
> > The reason for not having kref is that, each mhi_dev will be used by
> > maximum of 2 channels only. So thought that refcounting is not needed.
> > Please correct me if I'm wrong.
> 
> Please read section 11 of Documentation/process/coding-style.rst
> 

I have fixed it and will send the next iteration soon.

Thanks,
Mani

> thanks,
> 
> greg k-h