linux-kernel - Re: [GIT PULL] SG changes for 4.3

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Date:	Thu, 3 Sep 2015 08:31:45 -0600
From:	Jens Axboe <axboe@...com>
To:	Ming Lin <mlin@...nel.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] SG changes for 4.3

On 09/02/2015 10:28 PM, Ming Lin wrote:
> On Wed, Sep 2, 2015 at 3:50 PM, Jens Axboe <axboe@...com> wrote:
>> On 09/02/2015 04:41 PM, Jens Axboe wrote:
>>>
>>> On 09/02/2015 04:34 PM, Linus Torvalds wrote:
>>>>
>>>> Jens,
>>>>
>>>> On Wed, Sep 2, 2015 at 9:58 AM, Jens Axboe <axboe@...com> wrote:
>>>>>
>>>>>
>>>>> This pull request contains a set of scatter-gather related changes/fixes
>>>>> for 4.3. It contains:
>>>>
>>>>
>>>> This results in several new and annoying warnings. They may all be ok
>>>> code, but they are very distracting. Please stop introducing new
>>>> warnings to the build, because by now most of the warnings I see come
>>>> from the block layer.
>>>>
>>>>      block/blk-merge.c: In function ‘blk_queue_split’:
>>>>      include/linux/blkdev.h:1368:21: warning: ‘bvprv.bv_offset’ may be
>>>> used uninitialized in this function [-Wmaybe-uninitialized]
>>>>        ((bprv->bv_offset + bprv->bv_len) & queue_virt_boundary(q));
>>>>
>>>> (it gives this for bv_len too). The reason seems to be that disgusting
>>>> situation where "bvprv" is uninitiatlized unless "split" is true, and
>>>> the code looks like it is correct, but the compiler clearly has a hard
>>>> time seeing it. It took me a while too, so I can't really blame it.
>>>>
>>>> Either initialize bvprv to something explicit, or make the code clear
>>>> enough that the compiler can see that it is never used uninitialized.
>>>> Because those compiler warnings are sometimes real, and we can't just
>>>> ignore them.
>>>>
>>>> There was another type-based warning introduced by your core block
>>>> pull (size_t vs unsigned int).
>>>
>>>
>>> I think it's a repeat offender that got reintroduced. I'll fix it up.
>>
>>
>> This seems to make it happier. Will go out later in the merge window.
>>
>> https://urldefense.proofpoint.com/v1/url?u=http://git.kernel.dk/cgit/linux-block/commit/?h%3Dfor-linus%26id%3D5014c311baa2b21384321fa4a9f617a92e3e56f0&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=3JMVyziIyZtZ5cv9eWNLwQ%3D%3D%0A&m=japm7LD5hS2iGfc2KmNCva0tg%2FTlU%2BypJqbyuKQJk6U%3D%0A&s=dbea685c3231dae01cce41309c39c6c1597bd0dd1b4d6fbe5ee4caae86385fe8
>
> Thanks Jens.
>
> I didn't see these warnings with gcc 4.8.4.
> What gcc version did you use or need to turn on some config option to
> see the warning?

axboe@...ny:~ $ gcc --version
gcc (Ubuntu 5.1.0-0ubuntu11~14.04.1) 5.1.0

Looks like gcc is growing dumber.

-- 
Jens Axboe

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