Hi, scripts/get_maintainer.pl is your friend :) Please use it to Cc the relevant maintainers and reviewers next time.
Cheers, Lance On Thu, May 07, 2026 at 03:05:56PM +0800, Chen Wandun wrote: >madvise_collapse() computes a THP-aligned window from the caller's range: > > hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK /* round up */ > hend = end & HPAGE_PMD_MASK /* round down */ > >When the caller's range is smaller than one PMD (2 MiB) and/or not >PMD-aligned, hstart can end up greater than hend. In that case the >collapsing loop is correctly skipped, but the return value was computed >as ((hend - hstart) >> HPAGE_PMD_SHIFT): with hstart > hend the >subtraction wraps unsigned, producing a huge value, the comparison >"thps != 0" fires, and -EINVAL is returned instead of 0. > >A concrete example: > > /* both cover less than one THP; both should return 0 */ > madvise(aligned, PAGE_SIZE, MADV_COLLAPSE); /* OK, returns 0 */ > madvise(aligned + PAGE_SIZE, PAGE_SIZE, MADV_COLLAPSE); /* returns -EINVAL */ > >The fix moves the hstart/hend calculation before kmalloc_obj() and >returns 0 early when hstart >= hend. This also avoids the kmalloc, >mmgrab(), and lru_add_drain_all() calls for ranges that trivially >contain no PMD window. The same effect could be achieved by only >guarding the final return expression, but early-return keeps the >no-op path free of the allocator and drain overhead. > >Patch 1 fixes the kernel bug. >Patch 2 adds a selftest with two cases covering the hstart == hend >(aligned, was already correct) and hstart > hend (unaligned, was >broken) scenarios. > >Chen Wandun (2): > mm/khugepaged: fix spurious -EINVAL from sub-PMD MADV_COLLAPSE range > selftests/mm: add MADV_COLLAPSE sub-PMD range tests > > mm/khugepaged.c | 9 +- > tools/testing/selftests/mm/.gitignore | 1 + > tools/testing/selftests/mm/Makefile | 2 + > .../selftests/mm/ksft_madv_collapse.sh | 4 + > .../selftests/mm/madv_collapse_range.c | 141 ++++++++++++++++++ > tools/testing/selftests/mm/run_vmtests.sh | 5 + > 6 files changed, 159 insertions(+), 3 deletions(-) > create mode 100755 tools/testing/selftests/mm/ksft_madv_collapse.sh > create mode 100644 tools/testing/selftests/mm/madv_collapse_range.c > >-- >2.43.0 > >
