linux-kernel - Re: [PATCH] of: Fix issue where code would fall through to error case.

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Message-ID: <CAL_Jsq+eQYGq7ZtiQaerBk1SP=K1Wgd+b_2UGKFoRS4_s_8Fvg@mail.gmail.com>
Date:   Tue, 29 Nov 2016 09:06:08 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     Moritz Fischer <moritz.fischer.private@...il.com>,
        Moritz Fischer <moritz.fischer@...us.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        moritz@...e-entropy.org,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH] of: Fix issue where code would fall through to error case.

On Mon, Nov 28, 2016 at 9:30 AM, Frank Rowand <frowand.list@...il.com> wrote:
> On 11/26/16 13:39, Frank Rowand wrote:
>> On 11/23/16 13:58, Rob Herring wrote:
>>> On Thu, Nov 17, 2016 at 6:10 PM, Moritz Fischer
>>> <moritz.fischer.private@...il.com> wrote:
>>>> On Thu, Nov 17, 2016 at 4:02 PM, Frank Rowand <frowand.list@...il.com> wrote:
>>>>> On 11/17/16 15:40, Frank Rowand wrote:
>>>>>> On 11/17/16 15:25, Moritz Fischer wrote:
>>>>>>> No longer fall through into the error case that prints out
>>>>>>> an error if no error (err = 0) occurred.
>>>>>>>
>>>>>>> Fixes d9181b20a83(of: Add back an error message, restructured)
>>>>>>> Signed-off-by: Moritz Fischer <moritz.fischer@...us.com>
>>>>>>> ---
>>>>>>>  drivers/of/resolver.c | 6 +++++-
>>>>>>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/drivers/of/resolver.c b/drivers/of/resolver.c
>>>>>>> index 783bd09..785076d 100644
>>>>>>> --- a/drivers/of/resolver.c
>>>>>>> +++ b/drivers/of/resolver.c
>>>>>>> @@ -358,9 +358,13 @@ int of_resolve_phandles(struct device_node *overlay)
>>>>>>>
>>>>>>>              err = update_usages_of_a_phandle_reference(overlay, prop, phandle);
>>>>>>>              if (err)
>>>>>>> -                    break;
>>>>>>> +                    goto err_out;
>>>>>>>      }
>>>>>>>
>>>>>>> +    of_node_put(tree_symbols);
>>>>>>> +
>>>>>>> +    return 0;
>>>>>>> +
>>>>>>>  err_out:
>>>>>>>      pr_err("overlay phandle fixup failed: %d\n", err);
>>>>>>>  out:
>>>>>>
>>>>>> Thanks for catching that.
>>>>>>
>>>>>> Rob, please apply.
>>>>>>
>>>>>> Reviewed-by: Frank Rowand <frank.rowand@...sony.com>
>>>>>>
>>>>>> -Frank
>>>>>
>>>>> On second thought, isn't the common pattern when clean up is needed for
>>>>> both the no-error path and the error path something like:
>>>>>
>>>>>
>>>>>         out:
>>>>>                 of_node_put(tree_symbols);
>>>>>                 return err;
>>>>>
>>>>>         err_out:
>>>>>                 pr_err("overlay phandle fixup failed: %d\n", err);
>>>>>                 goto out;
>>>>>         }
>>>>>
>>>>>
>>>>> I don't have a strong opinion, whatever Rob wants to take is fine with me.
>>>>
>>>> Same here. I tried to avoid the jumping back part, but if that's the
>>>> common pattern,
>>>> I can submit a v2 doing that instead.
>>>
>>> Both are ugly. Just do:
>>>
>>> if (err)
>>>   pr_err(...);
>>>
>>> Rob
>>
>> Agreed.  Thanks for the touch of sanity Rob.
>>
>> -Frank
>
> I succumbed to looking only at the few lines of code above and not the
> fuller context of the file that the patch applies to.
>
> The proposed patch was fixing the problem that a normal completion
> of the for loop was falling through into the err_out label.  So what
> looks cleaner ("if (err) pr_err(...)") is actually not correct.

What!? The *only* problem was printing the error message in the err=0
case. All that needs to be fixed is not doing that. If we do that,
then we really only need 1 goto label.

Rob