On Mon, Apr 17, 2023 at 02:49:57PM +0100, Mark Rutland wrote: > On Mon, Apr 17, 2023 at 08:55:17PM +0800, kernel test robot wrote: > > Hi Mark, > > Hi, > > > FYI, the error/warning was bisected to this commit, please ignore it if it's irrelevant. > > I took a look, and this warning existed in the prior commit. All that has > changed is that it has moved from arch/arm64/mm/mmu.c to arch/arm64/mm/init.c. > > This commit is not to blame, and there is no regression here. > > The warning itself is bogus; more details on that below. Please ignore this. Sorry for this false positive. We've configured the bot to filter out the reports on this commit. Best Regards, Yujie > > tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master > > head: d3f2cd24819158bb70701c3549e586f9df9cee67 > > commit: b97547761b02cc95e0e6be827dc9ca9da8142761 [10286/12016] arm64: mm: move fixmap code to its own file > > config: arm64-buildonly-randconfig-r004-20230416 (https://download.01.org/0day-ci/archive/20230417/202304172004.r3IPh5Ja-lkp@xxxxxxxxx/config) > > compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project 9638da200e00bd069e6dd63604e14cbafede9324) > > reproduce (this is a W=1 build): > > wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross > > chmod +x ~/bin/make.cross > > # install arm64 cross compiling tool for clang build > > # apt-get install binutils-aarch64-linux-gnu > > # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=b97547761b02cc95e0e6be827dc9ca9da8142761 > > git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git > > git fetch --no-tags linux-next master > > git checkout b97547761b02cc95e0e6be827dc9ca9da8142761 > > # save the config file > > mkdir build_dir && cp config build_dir/.config > > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=arm64 olddefconfig > > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=arm64 SHELL=/bin/bash arch/arm64/mm/ > > > > If you fix the issue, kindly add following tag where applicable > > | Reported-by: kernel test robot <lkp@xxxxxxxxx> > > | Link: https://lore.kernel.org/oe-kbuild-all/202304172004.r3IPh5Ja-lkp@xxxxxxxxx/ > > > > All warnings (new ones prefixed by >>): > > > > >> arch/arm64/mm/fixmap.c:199:10: warning: variable 'bm_pudp' set but not used [-Wunused-but-set-variable] > > pud_t *bm_pudp; > > ^ > > 1 warning generated. > > > > > > vim +/bm_pudp +199 arch/arm64/mm/fixmap.c > > > :> 182 > > 183 /* > > 184 * Copy the fixmap region into a new pgdir. > > 185 */ > > 186 void __init fixmap_copy(pgd_t *pgdir) > > 187 { > > 188 if (!READ_ONCE(pgd_val(*pgd_offset_pgd(pgdir, FIXADDR_TOT_START)))) { > > 189 /* > > 190 * The fixmap falls in a separate pgd to the kernel, and doesn't > > 191 * live in the carveout for the swapper_pg_dir. We can simply > > 192 * re-use the existing dir for the fixmap. > > 193 */ > > 194 set_pgd(pgd_offset_pgd(pgdir, FIXADDR_TOT_START), > > 195 READ_ONCE(*pgd_offset_k(FIXADDR_TOT_START))); > > 196 } else if (CONFIG_PGTABLE_LEVELS > 3) { > > 197 pgd_t *bm_pgdp; > > 198 p4d_t *bm_p4dp; > > > 199 pud_t *bm_pudp; > > The full piece of code in question is: > > | } else if (CONFIG_PGTABLE_LEVELS > 3) { > | pgd_t *bm_pgdp; > | p4d_t *bm_p4dp; > | pud_t *bm_pudp; > ^ defined > > | /* > | * The fixmap shares its top level pgd entry with the kernel > | * mapping. This can really only occur when we are running > | * with 16k/4 levels, so we can simply reuse the pud level > | * entry instead. > | */ > | BUG_ON(!IS_ENABLED(CONFIG_ARM64_16K_PAGES)); > | bm_pgdp = pgd_offset_pgd(pgdp, FIXADDR_TOT_START); > | bm_p4dp = p4d_offset(bm_pgdp, FIXADDR_TOT_START); > | bm_pudp = pud_set_fixmap_offset(bm_p4dp, FIXADDR_TOT_START); > ^ set > > | pud_populate(&init_mm, bm_pudp, lm_alias(bm_pmd)); > ^ used > > | pud_clear_fixmap(); > | } else { > > What's happening here is that the config has CONFIG_PGTABLE_LEVELS=2, where the > above block is unreachable, but the warning is being generated for trivially > unreachable code. > > With that config, we'll use include/asm-generic/pgtable-nopmd.h, where > pud_populate() is defined as: > > | #define pud_populate(mm, pmd, pte) do { } while (0) > > ... and hence it's complaing that the (unreachable) definition and > initialization of bm_pudp is not used. > > If I reconfigure the kernel with 4K pages and 48-bit VAs so that > CONFIG_PGTABLE_LEVELS=4, the above warning isn't generated. > > Thanks, > Mark. >
