On Mon, May 25, 2020 at 10:48:08AM +0800, kbuild test robot wrote: > Hi Peter, > > Thank you for the patch! Perhaps something to improve: > > [auto build test WARNING on vhost/linux-next] > [also build test WARNING on linus/master v5.7-rc7] > [cannot apply to kvm/linux-next tip/auto-latest linux/master next-20200522] > [if your patch is applied to the wrong git tree, please drop us a note to help > improve the system. BTW, we also suggest to use '--base' option to specify the > base tree in git format-patch, please see https://stackoverflow.com/a/37406982] > > url: https://github.com/0day-ci/linux/commits/Peter-Xu/KVM-Dirty-ring-interface/20200524-070926 > base: https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git linux-next > config: s390-randconfig-s002-20200524 (attached as .config) > compiler: s390-linux-gcc (GCC) 9.3.0 > reproduce: > # apt-get install sparse > # sparse version: v0.6.1-240-gf0fe1cd9-dirty > # save the attached .config to linux build tree > make W=1 C=1 ARCH=s390 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' > > If you fix the issue, kindly add following tag as appropriate > Reported-by: kbuild test robot <lkp@xxxxxxxxx> > > All warnings (new ones prefixed by >>, old ones prefixed by <<): > > arch/s390/kvm/../../../virt/kvm/kvm_main.c: In function 'kvm_page_in_dirty_ring': > >> arch/s390/kvm/../../../virt/kvm/kvm_main.c:2932:16: warning: comparison of unsigned expression >= 0 is always true [-Wtype-limits] > 2932 | return (pgoff >= KVM_DIRTY_LOG_PAGE_OFFSET) && > | ^~ Should be a false positive, since when KVM_DIRTY_LOG_PAGE_OFFSET==0 (true for s390) then the code won't reach here at all due to the previous check [1]. I thought gcc should be able to directly remove the below code when it sees "if (1) return false;", but it seems not... I wanted to avoid using "#if" macros because I think it always makes the code harder to read (especially when nested). Maybe it's still ok to use one more time here. Thanks, > > vim +2932 arch/s390/kvm/../../../virt/kvm/kvm_main.c > > 2926 > 2927 static bool kvm_page_in_dirty_ring(struct kvm *kvm, unsigned long pgoff) > 2928 { > 2929 if (!KVM_DIRTY_LOG_PAGE_OFFSET) > 2930 return false; [1] > 2931 > > 2932 return (pgoff >= KVM_DIRTY_LOG_PAGE_OFFSET) && > 2933 (pgoff < KVM_DIRTY_LOG_PAGE_OFFSET + > 2934 kvm->dirty_ring_size / PAGE_SIZE); > 2935 } > 2936 -- Peter Xu
