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SubjectRe: [paulmck-rcu:dev.2022.05.18a] BUILD SUCCESS 9735325cf6f7eb6cdcf1ad875b49faa72f288f79
On Wed, May 25, 2022 at 12:22:11PM +0800, kernel test robot wrote:
> tree/branch: https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2022.05.18a
> branch HEAD: 9735325cf6f7eb6cdcf1ad875b49faa72f288f79 fixup! rcu-tasks: Scan running tasks for RCU Tasks Trace readers
>
> Unverified Warning (likely false positive, please contact us if interested):
>
> kernel/rcu/tasks.h:1514 rcu_tasks_trace_pregp_step() error: uninitialized symbol 'rtpcp'.

It did happen to point out a bug in this case, but the compiler cannot
know that the loop in which it is initialized must execute at least once
because there cannot be zero CPUs. So it really is always initialized,
so lack of initialization is not the problem. The problem instead is
that it will likely have the wrong value after the loop completes.

It could just as well be that the code following the loop wanted to
use the rtpcp corresponding to the last CPU visited by that loop, and
knowing that there will always be a last CPU.

So this diagnostic might sometimes be useful, and it might point out some
tricky bugs, but it is going to require a lot of human time and attention.

As always, choose wisely!

Thanx, Paul

> Warning ids grouped by kconfigs:
>
> gcc_recent_errors
> `-- i386-randconfig-m021
> `-- kernel-rcu-tasks.h-rcu_tasks_trace_pregp_step()-error:uninitialized-symbol-rtpcp-.
>
> elapsed time: 1725m
>
> configs tested: 130
> configs skipped: 3
>
> The following configs have been built successfully.
> More configs may be tested in the coming days.
>
> gcc tested configs:
> arm64 defconfig
> arm64 allyesconfig
> arm allmodconfig
> arm defconfig
> arm allyesconfig
> i386 randconfig-c001
> sh ul2_defconfig
> arc nsimosci_hs_smp_defconfig
> m68k mac_defconfig
> m68k sun3x_defconfig
> arm integrator_defconfig
> m68k hp300_defconfig
> arm cerfcube_defconfig
> arc nsimosci_hs_defconfig
> m68k amcore_defconfig
> arm imxrt_defconfig
> arm realview_defconfig
> sparc64 alldefconfig
> arm ezx_defconfig
> sh sh7710voipgw_defconfig
> powerpc warp_defconfig
> sh se7206_defconfig
> m68k alldefconfig
> arm multi_v4t_defconfig
> xtensa iss_defconfig
> mips loongson1b_defconfig
> um defconfig
> powerpc wii_defconfig
> sh r7780mp_defconfig
> nios2 3c120_defconfig
> ia64 defconfig
> riscv allnoconfig
> m68k allyesconfig
> m68k allmodconfig
> m68k defconfig
> nios2 defconfig
> arc allyesconfig
> csky defconfig
> nios2 allyesconfig
> alpha defconfig
> alpha allyesconfig
> h8300 allyesconfig
> xtensa allyesconfig
> arc defconfig
> sh allmodconfig
> s390 defconfig
> s390 allmodconfig
> parisc defconfig
> parisc64 defconfig
> parisc allyesconfig
> s390 allyesconfig
> sparc defconfig
> i386 allyesconfig
> sparc allyesconfig
> i386 defconfig
> i386 debian-10.3-kselftests
> i386 debian-10.3
> mips allyesconfig
> mips allmodconfig
> powerpc allyesconfig
> powerpc allnoconfig
> powerpc allmodconfig
> x86_64 randconfig-a006
> x86_64 randconfig-a004
> x86_64 randconfig-a002
> x86_64 randconfig-a002-20220523
> x86_64 randconfig-a001-20220523
> x86_64 randconfig-a003-20220523
> x86_64 randconfig-a006-20220523
> x86_64 randconfig-a004-20220523
> i386 randconfig-a004-20220523
> i386 randconfig-a001-20220523
> i386 randconfig-a003-20220523
> i386 randconfig-a002-20220523
> i386 randconfig-a006-20220523
> i386 randconfig-a005-20220523
> x86_64 randconfig-a011
> x86_64 randconfig-a013
> x86_64 randconfig-a015
> i386 randconfig-a012
> i386 randconfig-a014
> i386 randconfig-a016
> arc randconfig-r043-20220524
> s390 randconfig-r044-20220524
> riscv randconfig-r042-20220524
> arc randconfig-r043-20220523
> s390 randconfig-r044-20220522
> riscv defconfig
> riscv nommu_virt_defconfig
> riscv rv32_defconfig
> riscv nommu_k210_defconfig
> riscv allmodconfig
> riscv allyesconfig
> x86_64 rhel-8.3-kselftests
> um x86_64_defconfig
> um i386_defconfig
> x86_64 kexec
> x86_64 defconfig
> x86_64 allyesconfig
> x86_64 rhel-8.3
> x86_64 rhel-8.3-func
> x86_64 rhel-8.3-syz
> x86_64 rhel-8.3-kunit
>
> clang tested configs:
> arm mvebu_v5_defconfig
> mips rbtx49xx_defconfig
> riscv rv32_defconfig
> arm moxart_defconfig
> mips maltaup_defconfig
> powerpc mpc836x_mds_defconfig
> powerpc akebono_defconfig
> powerpc walnut_defconfig
> arm pcm027_defconfig
> powerpc g5_defconfig
> powerpc katmai_defconfig
> mips e55_defconfig
> powerpc obs600_defconfig
> x86_64 randconfig-a005
> x86_64 randconfig-a001
> x86_64 randconfig-a003
> i386 randconfig-a002
> i386 randconfig-a006
> i386 randconfig-a004
> x86_64 randconfig-a012
> x86_64 randconfig-a014
> x86_64 randconfig-a016
> i386 randconfig-a011
> i386 randconfig-a013
> i386 randconfig-a015
> hexagon randconfig-r041-20220523
> hexagon randconfig-r045-20220524
> hexagon randconfig-r041-20220524
>
> --
> 0-DAY CI Kernel Test Service
> https://01.org/lkp

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