An additional report: https://lore.kernel.org/lkml/20210623223015.GA315292@paulmck-ThinkPad-P17-Gen-1/ EOM On Fri, Jun 18, 2021 at 4:05 PM Nathan Chancellor <nathan@xxxxxxxxxx> wrote: > > On Fri, Jun 18, 2021 at 10:32:42AM +0530, Aneesh Kumar K.V wrote: > > On 6/17/21 11:32 PM, Nathan Chancellor wrote: > > > Rebuilt the CC list because most people were added based on the > > > incorrect bisect result. > > > > > > On Thu, Jun 17, 2021 at 02:51:49PM +0100, Matthew Wilcox wrote: > > > > On Thu, Jun 17, 2021 at 06:15:45PM +0530, Naresh Kamboju wrote: > > > > > On Thu, 17 Jun 2021 at 17:41, Naresh Kamboju <naresh.kamboju@xxxxxxxxxx> wrote: > > > > > > x86_64-linux-gnu-ld: mm/mremap.o: in function `move_pgt_entry': > > > > > > mremap.c:(.text+0x763): undefined reference to `__compiletime_assert_342' > > > > > > > > > > The git bisect pointed out the first bad commit. > > > > > > > > > > The first bad commit: > > > > > commit 928cf6adc7d60c96eca760c05c1000cda061604e > > > > > Author: Stephen Boyd <swboyd@xxxxxxxxxxxx> > > > > > Date: Thu Jun 17 15:21:35 2021 +1000 > > > > > module: add printk formats to add module build ID to stacktraces > > > > > > > > Your git bisect probably went astray. There's no way that commit > > > > caused that regression. > > > > > > My bisect landed on commit 83f85ac75855 ("mm/mremap: convert huge PUD > > > move to separate helper"). flush_pud_tlb_range() evaluates to > > > BUILD_BUG() when CONFIG_TRANSPARENT_HUGEPAGE is unset but this function > > > is present just based on the value of > > > CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD. > > > > > > $ make -skj(nproc) ARCH=x86_64 CC=clang O=build/x86_64 distclean allnoconfig mm/mremap.o > > > > > > $ llvm-readelf -s build/x86_64/mm/mremap.o &| rg __compiletime_assert > > > 21: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND __compiletime_assert_337 > > > > > > $ rg TRANSPARENT_ build/x86_64/.config > > > 450:CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE=y > > > 451:CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD=y > > > 562:# CONFIG_TRANSPARENT_HUGEPAGE is not set > > > > > > Not sure why this does not happen on newer clang versions, presumably > > > something with inlining decisions? Still seems like a legitimate issue > > > to me. > > > > > > > gcc 10 also doesn't give a build error. I guess that is because we evaluate > > > > if (pud_trans_huge(*old_pud) || pud_devmap(*old_pud)) { > > > > to if (0) with CONFIG_TRANSPARENT_HUGEPAGE disabled. > > > > switching that to if (1) do results in BUILD_BUG triggering. > > Thanks for pointing that out. I think what happens with clang-10 and > clang-11 is that move_huge_pud() gets inlined into move_pgt_entry() but > then the compiler does not figure out that the HPAGE_PUD case is dead so > the code sticks around, where as GCC and newer clang versions can figure > that out and eliminate that case. > > > Should we fix this ? > > Yes, I believe that we should. > > > modified mm/mremap.c > > @@ -336,7 +336,7 @@ static inline bool move_normal_pud(struct vm_area_struct > > *vma, > > } > > #endif > > > > -#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD > > +#if defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) && > > defined(CONFIG_TRANSPARENT_HUGEPAGE) > > static bool move_huge_pud(struct vm_area_struct *vma, unsigned long > > old_addr, > > unsigned long new_addr, pud_t *old_pud, pud_t *new_pud) > > { > > That works or we could mirror what has already been done for the > HPAGE_PMD case. No personal preference. > > diff --git a/mm/mremap.c b/mm/mremap.c > index 9a7fbec31dc9..5989d3990020 100644 > --- a/mm/mremap.c > +++ b/mm/mremap.c > @@ -460,7 +460,8 @@ static bool move_pgt_entry(enum pgt_entry entry, struct vm_area_struct *vma, > new_entry); > break; > case HPAGE_PUD: > - moved = move_huge_pud(vma, old_addr, new_addr, old_entry, > + moved = IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && > + move_huge_pud(vma, old_addr, new_addr, old_entry, > new_entry); > break; > > > Cheers, > Nathan -- Thanks, ~Nick Desaulniers
