Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.31 as permitted sender) client-ip=23.128.96.31;
Date:   Sun, 24 Sep 2023 12:16:08 +0000
From:   "Dr. David Alan Gilbert" <dave@treblig.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc:     matthew.brost@intel.com, mgreer@animalcreek.com,
        linux-kernel@vger.kernel.org, airlied@gmail.com,
        intel-gfx@lists.freedesktop.org
Subject: Re: ERR_PTR(0) in a couple of places
Message-ID: <ZRAoiGafRSv7SM6C@gallifrey>
References: <ZQ+Fo9WKyGphwI8R@gallifrey>
 <b3813a4e-3956-254c-a7cf-0fca65dc2cdd@linaro.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
In-Reply-To: <b3813a4e-3956-254c-a7cf-0fca65dc2cdd@linaro.org>
User-Agent: Mutt/2.2.9 (2022-11-12)
Precedence: bulk

* Krzysztof Kozlowski (krzysztof.kozlowski@linaro.org) wrote:
> On 24/09/2023 02:41, Dr. David Alan Gilbert wrote:
> > Hi,
> >   I randomly noticed there are a couple of places in the kernel that
> > do
> >    ERR_PTR(0);
> > 
> > and thought that was odd - shouldn't those just be NULL's ?
> > 
> > 1) i915
> >   drivers/gpu/drm/i915/gt/uc/selftest_guc_multi_lrc.c : 47
> > 
> >     if (i <= 1)
> >       return ERR_PTR(0);
> > 
> >   from f9d72092cb490 
> > 
> > 2) trf7970a
> >   drivers/nfc/trf7970a.c : 896
> > 
> >       trf->ignore_timeout =
> >          !cancel_delayed_work(&trf->timeout_work);
> >       trf->rx_skb = ERR_PTR(0);
> 
> I would guess that code is relying on rx_skb being valid pointer or ERR
> (if (!IS_ERR(...))).

If seems mixed, that function calls trf7970a_send_upstream which has
both:

  if (trf->rx_skb && !IS_ERR(trf->rx_skb) && !trf->aborting)
    print_hex_dump_debug("trf7970a rx data: ", DUMP_PREFIX_NONE,
             16, 1, trf->rx_skb->data, trf->rx_skb->len,
             false);
and
    if (!IS_ERR(trf->rx_skb)) {
      kfree_skb(trf->rx_skb);
      trf->rx_skb = ERR_PTR(-ECANCELED);
    }

It's not clear to me whether it's expecteing that 2nd if to happen or
not.

I notice err.h gained a IS_ERR_OR_NULL to help that case as well.

Dave

> Best regards,
> Krzysztof
> 
-- 
 -----Open up your eyes, open up your mind, open up your code -------   
/ Dr. David Alan Gilbert    |       Running GNU/Linux       | Happy  \ 
\        dave @ treblig.org |                               | In Hex /
 \ _________________________|_____ http://www.treblig.org   |_______/