On Wed, Jun 23, 2021 at 3:30 PM Paul E. McKenney [off-list ref] wrote:

Hello, Aneesh!

Yesterday evening's next-20210622 testing gave me the following
kernel-build error:

ld: mm/mremap.o: in function `move_huge_pud':
/home/git/linux-next/mm/mremap.c:372: undefined reference to `__compiletime_assert_395'

Bisection landed on this commit:

257121c5aabe ("mm/mremap: convert huge PUD move to separate helper")

I have no idea how this commit relates to that error message, but
reverting this commit on top of next-20210622 really does get rid of
the problem.

The following reproducer provokes this error:

tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --torture lock --configs LOCK07 --build-only --kconfig "CONFIG_DEBUG_LOCK_ALLOC=y CONFIG_PROVE_LOCKING=y" --kmake-arg "CC=clang-11"

Run the above command in the top-level directory of your -next source
tree, and using this compiler:

$ clang-11 -v
Ubuntu clang version 11.1.0-++20210428103817+1fdec59bffc1-1~exp1~20210428204431.166
Target: x86_64-pc-linux-gnu

Thoughts?

                                                        Thanx, Paul

++beers_owed; for the report and bisection. Also reported
https://lore.kernel.org/lkml/YM0mrZIPM+sWTDHf@Ryzen-9-3900X.localdomain/ (local),
let's chat over there.

-- 
Thanks,
~Nick Desaulniers