linux-kernel - Re: [PATCH v2] staging: gpib: cb7210: Add error handling

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Message-ID: <2024122133-outskirts-causing-099a@gregkh>
Date: Sat, 21 Dec 2024 10:43:14 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Nihar Chaithanya <niharchaithanya@...il.com>
Cc: dpenkler@...il.com, dan.carpenter@...aro.org, roheetchavan@...il.com,
	arnd@...db.de, linux-staging@...ts.linux.dev,
	linux-kernel@...r.kernel.org, skhan@...uxfoundation.org
Subject: Re: [PATCH v2] staging: gpib: cb7210: Add error handling

On Sat, Dec 21, 2024 at 10:25:41AM +0100, Greg KH wrote:
> On Sat, Dec 21, 2024 at 02:41:25PM +0530, Nihar Chaithanya wrote:
> > The if condition in cb7210_init_module() would always fail as
> > the value of err is constantly 0. The function
> > cb_pcmcia_init_module() can be refactored into a single line,
> > and can be replaced entirely with pcmcia_register_driver().
> > 
> > Replace redundant cb_pcmcia_init_module() with
> > pcmcia_register_driver() which returns appropriate error code if
> > it fails. Handle the error if it fails and print the debug message.
> > 
> > This issue was reported by Coverity Scan.
> > Report:
> > CID 1635894: (#1 of 1): 'Constant' variable guards dead code (DEADCODE)
> > dead_error_line: Execution cannot reach this statement: return -1;.
> > 
> > Signed-off-by: Nihar Chaithanya <niharchaithanya@...il.com>
> > ---
> > v1 --> v2: Replaced the redundant cb_pcmcia_init_module() with
> > 	   pcmcia_register_driver().
> > 
> >  drivers/staging/gpib/cb7210/cb7210.c | 13 ++++---------
> >  1 file changed, 4 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/staging/gpib/cb7210/cb7210.c b/drivers/staging/gpib/cb7210/cb7210.c
> > index 63df7f3eb3f3..abd6632d8448 100644
> > --- a/drivers/staging/gpib/cb7210/cb7210.c
> > +++ b/drivers/staging/gpib/cb7210/cb7210.c
> > @@ -1351,12 +1351,6 @@ static struct pcmcia_driver cb_gpib_cs_driver = {
> >  	.resume		= cb_gpib_resume,
> >  };
> >  
> > -int cb_pcmcia_init_module(void)
> > -{
> > -	pcmcia_register_driver(&cb_gpib_cs_driver);
> > -	return 0;
> > -}
> > -
> >  void cb_pcmcia_cleanup_module(void)
> >  {
> >  	DEBUG(0, "cb_gpib_cs: unloading\n");
> > @@ -1526,11 +1520,12 @@ static int __init cb7210_init_module(void)
> >  	gpib_register_driver(&cb_pcmcia_interface, THIS_MODULE);
> >  	gpib_register_driver(&cb_pcmcia_accel_interface, THIS_MODULE);
> >  	gpib_register_driver(&cb_pcmcia_unaccel_interface, THIS_MODULE);
> > -	err += cb_pcmcia_init_module();
> > +	err = pcmcia_register_driver(&cb_gpib_cs_driver);
> >  #endif
> > -	if (err)
> > +	if (err) {
> > +		pr_err("cb7210: registering PCMCIA driver with the bus core failed\n");
> >  		return -1;
> 
> Not your issue, but "-1" is not a valid error number, shouldn't this be
> returning a real error (i.e. the one that was returned?)
> 
> And err += is crazy, thanks for removing that, BUT you forgot to unwind
> the previous functions so now if pcmcia_register_driver() fails, you
> have a semi-registered system and then the module will unload (as init
> fails) and bad things will happen :(
> 
> So you kind of just made the code worse overall, not better, which
> really isn't a good idea for a "bugfix" that covertity was trying to
> point out.

And (this is taking you down a path that is much larger than you
expected to just fix this one issue, sorry), it looks like
gpib_register_driver() can fail, so it MUST return an error value so you
can properly unwind from it.  So that too needs to be fixed up here
(also minor nit, gpib_register_driver() should not be calling pr_info(),
but that's a different issue.)

In all, there are loads of tiny things like this to fix up in the gpib
code, which is great, have fun!

thanks,

greg k-h