linux-kernel - Re: [PATCH/RFC] RDMA/iwpm: Fix uninitialized error code in iwpm_send

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Date:   Thu, 16 Nov 2017 12:32:03 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Tatyana Nikolova <Tatyana.E.Nikolova@...el.com>,
        Roland Dreier <roland@...estorage.com>,
        Doug Ledford <dledford@...hat.com>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH/RFC] RDMA/iwpm: Fix uninitialized error code in iwpm_send_mapinfo()

On Thu, Nov 16, 2017 at 12:05 PM, Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> Hi Arnd,
>
> On Thu, Nov 16, 2017 at 11:50 AM, Arnd Bergmann <arnd@...db.de> wrote:
>> On Thu, Nov 16, 2017 at 11:26 AM, Geert Uytterhoeven
>> <geert@...ux-m68k.org> wrote:
>>> With gcc-4.1.2:
>>>
>>>     drivers/infiniband/core/iwpm_util.c: In function ‘iwpm_send_mapinfo’:
>>>     drivers/infiniband/core/iwpm_util.c:647: warning: ‘ret’ may be used uninitialized in this function
>>>
>>> Indeed, if nl_client is not found in any of the scanned has buckets, ret
>>> will be used uninitialized.
>>>
>>> Preinitialize ret to zero to fix this.
>>>
>>> Fixes: 30dc5e63d6a5ad24 ("RDMA/core: Add support for iWARP Port Mapper user space service")
>>> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>>> ---
>>> RFC as I have no idea if this can ever happen, and if yes, what's the
>>> correct behavior to handle it:
>>>   - return 0,
>>>   - return an error code,
>>>   - don't send anything,
>>>   - anything else?
>>
>> This looks like a reasonable warning. I don't see on my box with any compiler
>> version. Do you have a configuration I can use to reproduce it, I'd just like
>> to see out of curiosity which other compilers report it.
>
> m68k/allmodconfig

I see my problem now, my randconfig test series has a patch I never sent
out, see https://pastebin.com/ZJDHP7g4 ;-)

With plan linux-next, I see the warning on x86 with gcc-4.3 and older, but
not on newer gcc versions or clang (I tried them all).

I also see that x86 builds broke again in recent kernels with gcc-4.2
and older unless you revert ec1e1b610917 ("objtool: Prevent GCC
from merging annotate_unreachable(), take 2").

       Arnd