netdev - Re: [PATCH] ptp: Set lookup cookie when creating a PTP PPS source.

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Date:   Tue, 6 Jul 2021 17:26:30 -0700
From:   Jonathan Lemon <jonathan.lemon@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Richard Cochran <richardcochran@...il.com>, netdev@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH] ptp: Set lookup cookie when creating a PTP PPS source.

On Fri, Jul 02, 2021 at 03:39:36AM +0300, Vladimir Oltean wrote:
> On Mon, Jun 28, 2021 at 04:38:35PM -0700, Richard Cochran wrote:
> > On Mon, Jun 28, 2021 at 11:25:33AM -0700, Jonathan Lemon wrote:
> > > When creating a PTP device, the configuration block allows
> > > creation of an associated PPS device.  However, there isn't
> > > any way to associate the two devices after creation.
> > >
> > > Set the PPS cookie, so pps_lookup_dev(ptp) performs correctly.
> >
> > Setting lookup_cookie is harmless, AFAICT, but I wonder about the use
> > case.  The doc for pps_lookup_dev() says,
> 
> Harmless you say?
> 
> Let's look at the code in a larger context:
> 
>  struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
>  				     struct device *parent)
>  {
>  	struct ptp_clock *ptp;
>  
>  	...
>  	ptp = kzalloc(...);
>  	...
>  	ptp->info = info;
>  	...
>  
>  	if (ptp->info->do_aux_work) {
>  		...
> +		ptp->pps_source->lookup_cookie = ptp;
>  	}
>  
>  	/* Register a new PPS source. */
>  	if (info->pps) {
>  		struct pps_source_info pps;
>  		...
>  		ptp->pps_source = pps_register_source(&pps, PTP_PPS_DEFAULTS);
>  		...
>  	}
> 
> Notice anything out of the ordinary?
> Like perhaps the fact that ptp->pps_source is an arbitrary NULL pointer
> at the time the assignment to ->lookup_cookie is being made, because it
> is being created later?
> 
> How on earth is this patch supposed to work?

It was added to the wrong code block.  Checking my tree, I seem to have
it located twice - probably a bad patch that I didn't notice, and since
I don't have an do_aux_work, the first one didn't trigger.

Correction follows.
-- 
Jonathan