On 2019/07/15 22:56, Jens Axboe wrote: > 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@xxxxxxxxx> >>> >>> 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? It is a false positive: if sd_zbc_check_zones() returns success, zone_blocks is always initialized. The zone_blocks variable is not initialized only if sd_zbc_check_zones() fails, but in that case this variable is not used at all. My guess is that gcc 7.4 warning is due to the error path, while gcc 9.1 does a better job at detecting that the variable is not used in failure cases. -- Damien Le Moal Western Digital Research
