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

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Message-ID: <583DB269.9070208@gmail.com>
Date:   Tue, 29 Nov 2016 08:52:57 -0800
From:   Frank Rowand <frowand.list@...il.com>
To:     Rob Herring <robh+dt@...nel.org>
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 11/29/16 07:06, Rob Herring wrote:
> 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

I misread your original suggestion to mean to put the "if (err) pr_err(...)"
inside the for loop, where Moritz had made his changes.

Now I understand what you really meant, to put the "if (err) pr_err(...)"
after the for loop.

Yes, that is a good way to do it.

Sorry for the extra noise....

-Frank