linux-kernel - Re: [PATCH v2 1/4] driver core: Ignore 0 in dev_err

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Message-ID: <4e8fa6fa-89aa-422f-b603-e2a3e1a2c704@stanley.mountain>
Date: Mon, 2 Sep 2024 14:10:41 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Hans de Goede <hdegoede@...hat.com>, linux-kernel@...r.kernel.org,
	platform-driver-x86@...r.kernel.org,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Daniel Scally <djrscally@...il.com>
Subject: Re: [PATCH v2 1/4] driver core: Ignore 0 in dev_err_probe()

On Mon, Sep 02, 2024 at 01:16:17PM +0300, Andy Shevchenko wrote:
> On Sat, Aug 31, 2024 at 11:53:51AM +0300, Dan Carpenter wrote:
> > On Sat, Aug 31, 2024 at 11:25:54AM +0300, Dan Carpenter wrote:
> > > On Thu, Aug 22, 2024 at 04:05:38PM +0300, Andy Shevchenko wrote:
> > > > In the similar way, ignore 0 error code (AKA "success") in
> > > > dev_err_probe(). This helps to simplify a code such as
> > > > 
> > > >   if (ret < 0)
> > > >     return dev_err_probe(int3472->dev, ret, err_msg);
> > > > 
> > > >   return ret;
> > > > 
> > > > to
> > > > 
> > > >   return dev_err_probe(int3472->dev, ret, err_msg);
> > > > 
> > > > Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> > > > Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > > 
> > > This is a terrible idea because currently Smatch is able to detect about one
> > > bug per month where someone unintentionally passes the wrong error variable
> > > to dev_err_probe().
> 
> How many cases you know where smatch is false positive about this?
> 

This check has a very low false positive rate.  There is only one potential
false positive in the current linux-next.  Let me add Baolin Wang to get his
take on this.  I never mentioned reported this warning because the code was old
when I wrote the check.

drivers/spi/spi-sprd-adi.c
   550          ret = of_hwspin_lock_get_id(np, 0);
   551          if (ret > 0 || (IS_ENABLED(CONFIG_HWSPINLOCK) && ret == 0)) {

Is it possible for the CONFIG_ to not be enabled but ret is zero?

   552                  sadi->hwlock =
   553                          devm_hwspin_lock_request_specific(&pdev->dev, ret);
   554                  if (!sadi->hwlock) {
   555                          ret = -ENXIO;
   556                          goto put_ctlr;
   557                  }
   558          } else {
   559                  switch (ret) {
   560                  case -ENOENT:
   561                          dev_info(&pdev->dev, "no hardware spinlock supplied\n");
   562                          break;
   563                  default:
   564                          dev_err_probe(&pdev->dev, ret, "failed to find hwlock id\n");
                                                          ^^^

   565                          goto put_ctlr;
   566                  }
   567          }


> I believe the number is only a few at most, which means that you may easily
> detect this still with this change being applied, i.e. "anything that
> terminates function flow with code 0, passed to dev_err_probe(), is
> suspicious".
> 

I think you mean the opposite of what you wrote?  That if we're passing zero to
dev_err_probe() and it's the last line in a function it's *NOT* suspicious?
Otherwise, I don't really understand the heuristic you're proposing.

regards,
dan carpenter