Re: [block:for-linus 20/23] include/linux/kernel.h:62:48: warning: 'zone_blocks' may be used uninitialized in this function

From: Jens Axboe <axboe@kernel.dk>
To: Damien Le Moal <Damien.LeMoal@wdc.com>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Cc: Christoph Hellwig <hch@lst.de>,
	"Martin K. Petersen" <martin.petersen@oracle.com>
Subject: Re: [block:for-linus 20/23] include/linux/kernel.h:62:48: warning: 'zone_blocks' may be used uninitialized in this function
Date: Mon, 15 Jul 2019 07:56:36 -0600	[thread overview]
Message-ID: <279546ac-9089-d5fc-f26c-9e46db269623@kernel.dk> (raw)
In-Reply-To: <BYAPR04MB5816C2EFC9D3C9FEF6DCCD2CE7CF0@BYAPR04MB5816.namprd04.prod.outlook.com>

On 7/14/19 11:43 PM, Damien Le Moal wrote:
> On 2019/07/13 18:10, kbuild test robot wrote:
>> tree:   https://kernel.googlesource.com/pub/scm/linux/kernel/git/axboe/linux-block.git for-linus
>> head:   787c79d6393fc028887cc1b6066915f0b094e92f
>> commit: b091ac616846a1da75b1f2566b41255ce7f0e0a6 [20/23] sd_zbc: Fix report zones buffer allocation
>> config: c6x-allyesconfig (attached as .config)
>> compiler: c6x-elf-gcc (GCC) 7.4.0
>> reproduce:
>>          wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>>          chmod +x ~/bin/make.cross
>>          git checkout b091ac616846a1da75b1f2566b41255ce7f0e0a6
>>          # save the attached .config to linux build tree
>>          GCC_VERSION=7.4.0 make.cross ARCH=c6x
>>
>> If you fix the issue, kindly add following tag
>> Reported-by: kbuild test robot <lkp@intel.com>
>>
>> Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
>> http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings
>>
>> All warnings (new ones prefixed by >>):
>>
>>     In file included from include/asm-generic/bug.h:18:0,
>>                      from arch/c6x/include/asm/bug.h:12,
>>                      from include/linux/bug.h:5,
>>                      from include/linux/thread_info.h:12,
>>                      from include/asm-generic/current.h:5,
>>                      from ./arch/c6x/include/generated/asm/current.h:1,
>>                      from include/linux/sched.h:12,
>>                      from include/linux/blkdev.h:5,
>>                      from drivers//scsi/sd_zbc.c:11:
>>     drivers//scsi/sd_zbc.c: In function 'sd_zbc_read_zones':
>>>> include/linux/kernel.h:62:48: warning: 'zone_blocks' may be used uninitialized in this function [-Wmaybe-uninitialized]
>>      #define __round_mask(x, y) ((__typeof__(x))((y)-1))
>>                                                     ^
>>     drivers//scsi/sd_zbc.c:464:6: note: 'zone_blocks' was declared here
>>       u32 zone_blocks;
>>           ^~~~~~~~~~~
> [...]
> 
> Jens,
> 
> This warning does not show up on x86_64 native build with gcc 9.1.
> I just sent a patch to remove the warning, but I do not have a c6x cross
> compilation environment available so the patch was checked only on x86.

Is it a false positive, or is it legit?

-- 
Jens Axboe