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

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Date:   Wed, 12 Feb 2020 00:41:47 +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 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. And we really
needed to NULL the mhi_dev to avoid any dangling reference to it. 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.

Thanks,
Mani

> > +
> > +	if (mhi_dev->dl_chan)
> > +		mhi_dev->dl_chan->mhi_dev = NULL;
> 
> Same here.
> 
> thanks,
> 
> greg k-h