On 5/9/26 17:47, Lance Yang wrote:
Hi,
scripts/get_maintainer.pl is your friend :)
Please use it to Cc the relevant maintainers and reviewers next time.
Many thanks for your kind reminder :)
I will do it next time.
Best regards,
Wandun
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
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2.43.0
