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

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Date:	Wed, 2 Sep 2015 21:28:26 -0700
From:	Ming Lin <mlin@...nel.org>
To:	Jens Axboe <axboe@...com>
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 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.
>
> http://git.kernel.dk/cgit/linux-block/commit/?h=for-linus&id=5014c311baa2b21384321fa4a9f617a92e3e56f0

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?
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