linux-kernel - Re: [PATCH v2 00/11] getting back -Wmaybe-uninitialized

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Date:   Sat, 12 Nov 2016 13:27:12 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        sayli karnik <karniksayli1995@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anna Schumaker <anna.schumaker@...app.com>,
        "David S. Miller" <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ilya Dryomov <idryomov@...il.com>,
        Javier Martinez Canillas <javier@....samsung.com>,
        Jiri Kosina <jikos@...nel.org>,
        Ley Foon Tan <lftan@...era.com>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michal Marek <mmarek@...e.com>,
        Russell King <linux@...linux.org.uk>,
        Sean Young <sean@...s.org>,
        Sebastian Ott <sebott@...ux.vnet.ibm.com>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        arcml <"linux-snps -arc"@lists.infradead.org>,
        nios2-dev@...ts.rocketboards.org,
        linux-s390 <linux-s390@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        gregkh@...uxfoundation.org
Subject: Re: [PATCH v2 00/11] getting back -Wmaybe-uninitialized

On 11/11/16 19:49, Arnd Bergmann wrote:
> On Friday, November 11, 2016 9:13:00 AM CET Linus Torvalds wrote:
>> On Thu, Nov 10, 2016 at 8:44 AM, Arnd Bergmann <arnd@...db.de> wrote:
>>>
>>> Please merge these directly if you are happy with the result.
>>
>> I will take this.
> 
> Thanks a lot!
>  
>> I do see two warnings, but they both seem to be valid and recent,
>> though, so I have no issues with the spurious cases.
> 
> Ok, both of them should have my fixes coming your way already.
> 
>> Warning #1:
>>
>>   sound/soc/qcom/lpass-platform.c: In function ‘lpass_platform_pcmops_open’:
>>   sound/soc/qcom/lpass-platform.c:83:29: warning: ‘dma_ch’ may be used
>> uninitialized in this function [-Wmaybe-uninitialized]
>>     drvdata->substream[dma_ch] = substream;
>>     ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~
>>
>> and 'dma_ch' usage there really is crazy and wrong. Broken by
>> 022d00ee0b55 ("ASoC: lpass-platform: Fix broken pcm data usage")
> 
> Right, the patches crossed here, the bugfix patch that introduced
> this came into linux-next over the kernel summit, and the fix I
> sent on Tuesday made it into Mark Brown's tree on Wednesday but not
> before you pulled alsa tree. It should be fixed the next time you
> pull from the alsa tree, the commit is
> 
> 3b89e4b77ef9 ("ASoC: lpass-platform: initialize dma channel number")
>  
>> Warning #2 is not a real bug, but it's reasonable that gcc doesn't
>> know that storage_bytes (chip->read_size) has to be 2/4. Again,
>> introduced recently by commit 231147ee77f3 ("iio: maxim_thermocouple:
>> Align 16 bit big endian value of raw reads"), so you didn't see it.
> 
> This is the one I mentioned in the commit message as one that
> is fixed in linux-next and that should make it in soon.
> 
>>   drivers/iio/temperature/maxim_thermocouple.c: In function
>> ‘maxim_thermocouple_read_raw’:
>>   drivers/iio/temperature/maxim_thermocouple.c:141:5: warning: ‘ret’
>> may be used uninitialized in this function [-Wmaybe-uninitialized]
>>     if (ret)
>>        ^
>>   drivers/iio/temperature/maxim_thermocouple.c:128:6: note: ‘ret’ was
>> declared here
>>     int ret;
>>         ^~~
>>
>> and I guess that code can just initialize 'ret' to '-EINVAL' or
>> something to just make the theoretical "somehow we had a wrong
>> chip->read_size" case error out cleanly.
> 
> Right, that was my conclusion too. I sent the bugfix on Oct 25
> for linux-next but it didn't make it in until this Monday, after
> you pulled the patch that introduced it on Oct 29.
> 
> The commit in staging-testing is
> 32cb7d27e65d ("iio: maxim_thermocouple: detect invalid storage size in read()")
> 
> Greg and Jonathan, I see now that this is part of the 'iio-for-4.10b'
> branch, so I suspect you were not planning to send this before the
> merge window. Could you make sure this ends up in v4.9 so we get
> a clean build when -Wmaybe-uninitialized gets enabled again?
I'll queue this up and send a pull to Greg tomorrow.

Was highly doubtful that a false warning suppression (be it an
understandable one) was worth sending mid cycle, hence it was
taking the slow route.

Jonathan
> 
> 	Arnd
>