linux-kernel - Re: [PATCH] net: dsa: mv88e6xxx: initialize return variable on declaration

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Message-ID: <20211207140647.6926a3e7@thinkpad>
Date:   Tue, 7 Dec 2021 14:06:47 +0100
From:   Marek Behún <kabel@...nel.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Andrew Lunn <andrew@...n.ch>, Ameer Hamza <amhamza.mgc@...il.com>,
        vivien.didelot@...il.com, f.fainelli@...il.com, olteanv@...il.com,
        davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: dsa: mv88e6xxx: initialize return variable on
 declaration

On Mon, 6 Dec 2021 16:25:10 -0800
Jakub Kicinski <kuba@...nel.org> wrote:

> On Mon, 6 Dec 2021 23:29:53 +0100 Marek Behún wrote:
> > On Mon, 6 Dec 2021 14:21:03 +0100
> > Andrew Lunn <andrew@...n.ch> wrote:
> >   
> > > On Mon, Dec 06, 2021 at 04:32:19PM +0500, Ameer Hamza wrote:    
> > > > Uninitialized err variable defined in mv88e6393x_serdes_power
> > > > function may cause undefined behaviour if it is called from
> > > > mv88e6xxx_serdes_power_down context.
> > > > 
> > > > Addresses-Coverity: 1494644 ("Uninitialized scalar variable")
> > > > 
> > > > Signed-off-by: Ameer Hamza <amhamza.mgc@...il.com>
> > > > ---
> > > >  drivers/net/dsa/mv88e6xxx/serdes.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/net/dsa/mv88e6xxx/serdes.c b/drivers/net/dsa/mv88e6xxx/serdes.c
> > > > index 55273013bfb5..33727439724a 100644
> > > > --- a/drivers/net/dsa/mv88e6xxx/serdes.c
> > > > +++ b/drivers/net/dsa/mv88e6xxx/serdes.c
> > > > @@ -1507,7 +1507,7 @@ int mv88e6393x_serdes_power(struct mv88e6xxx_chip *chip, int port, int lane,
> > > >  			    bool on)
> > > >  {
> > > >  	u8 cmode = chip->ports[port].cmode;
> > > > -	int err;
> > > > +	int err = 0;
> > > >  
> > > >  	if (port != 0 && port != 9 && port != 10)
> > > >  		return -EOPNOTSUPP;      
> > > 
> > > Hi Marek
> > > 
> > > This warning likely comes from cmode not being a SERDES mode, and that
> > > is not handles in the switch statementing. Do we want an
> > > 
> > > default:
> > > 	err = EINVAL;
> > > 
> > > ?  
> > 
> > currently all the .serdes_power() methods return 0 for non-serdes ports.
> > This is because the way it is written, these methods are not called if
> > there is not a serdes lane for a given port.
> > 
> > For this issue with err variable undefined, to fix it we should simply
> > set int err=0 at the beginning of mv88e6393x_serdes_power(), to make it
> > behave like other serdes_power() methods do in serdes.c.  
> 
> Any objections to using a default case in the switch statement, tho?
> I agree with Andrew that default statement would make the reasoning
> clearer than just setting the variable at the start of the function.

No objection, just that it should be done for all the serdes_power()
methods in serdes.c.

Marek