linux-kernel - Re: [PATCH] usb: typec: tcpm: Export partner Source Capabilities

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Message-ID: <20190131182213.GB17285@roeck-us.net>
Date:   Thu, 31 Jan 2019 10:22:13 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Kyle Tso <kyletso@...gle.com>, heikki.krogerus@...ux.intel.com,
        badhri@...gle.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: typec: tcpm: Export partner Source Capabilities

On Thu, Jan 31, 2019 at 08:02:38AM +0100, Greg KH wrote:
> On Thu, Jan 31, 2019 at 11:54:11AM +0800, Kyle Tso wrote:
> > Provide a function to get the partner Source Capabilities.
> > 
> > Signed-off-by: Kyle Tso <kyletso@...gle.com>
> > ---
> >  drivers/usb/typec/tcpm/tcpm.c | 23 +++++++++++++++++++++++
> >  include/linux/usb/tcpm.h      |  1 +
> >  2 files changed, 24 insertions(+)
> > 
> > diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> > index f1d3e54210df..29cd84ba9960 100644
> > --- a/drivers/usb/typec/tcpm/tcpm.c
> > +++ b/drivers/usb/typec/tcpm/tcpm.c
> > @@ -4494,6 +4494,29 @@ int tcpm_update_sink_capabilities(struct tcpm_port *port, const u32 *pdo,
> >  }
> >  EXPORT_SYMBOL_GPL(tcpm_update_sink_capabilities);
> >  
> > +/*
> > + * Don't call this function in interrupt context. Caller needs to free the
> > + * memory itself.
> > + */
> > +int tcpm_get_partner_src_caps(struct tcpm_port *port, u32 **src_pdo)
> > +{
> > +	unsigned int nr_pdo;
> > +
> > +	if (port->nr_source_caps == 0)
> > +		return -ENODATA;
> > +
> > +	*src_pdo = kcalloc(port->nr_source_caps, sizeof(u32), GFP_KERNEL);
> > +	if (!src_pdo)
> > +		return -ENOMEM;
> > +
> > +	mutex_lock(&port->lock);
> > +	nr_pdo = tcpm_copy_pdos(*src_pdo, port->source_caps,
> > +				port->nr_source_caps);
> > +	mutex_unlock(&port->lock);

The mutex use here suggests that the data can be updated while being
copied. But that suggests that port->nr_source_caps can change as
well and may no longer be current after mutex_lock().

> > +	return nr_pdo;
> > +}
> > +EXPORT_SYMBOL_GPL(tcpm_get_partner_src_caps);
> 
> We don't add new functions that no one uses :(
> 

I am also concerned about the API itself; passing a pointer to be freed
by the caller invites memory leaks.

Guenter