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mm/hugetlb: restore reservation on error in hugetlb folio copy paths

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Two sites in mm/hugetlb.c allocate a hugetlb folio via
alloc_hugetlb_folio() (consuming a VMA reservation) and then call
copy_user_large_folio(), which became int-returning in commit 1cb9dc4b47
("mm: hwpoison: support recovery from HugePage copy-on-write faults") and
can now fail (e.g.  -EHWPOISON on a hwpoisoned source page).  On the
failure path, folio_put() restores the global hugetlb pool count through
free_huge_folio(), but the per-VMA reservation map entry is left marked
consumed:

  - hugetlb_mfill_atomic_pte() resubmission path (UFFDIO_COPY)
  - copy_hugetlb_page_range() fork-time CoW path when
    hugetlb_try_dup_anon_rmap() fails (rare: pinned hugetlb anon
    folio under fork)

User-visible effect: on UFFDIO_COPY into a private hugetlb VMA where the
resubmission copy fails, the reservation for that address is leaked from
the VMA's reserve map.  A subsequent fault at the same address takes the
no-reservation path, and under hugetlb pool pressure the task is SIGBUSed
at an address it had previously reserved.  The fork-time CoW path leaks
the same way in the child VMA's reserve map, though it requires the much
rarer combination of pinned hugetlb anon page + hwpoisoned source.

Add the missing restore_reserve_on_error() call before folio_put() on both
error paths.

Link: https://lore.kernel.org/20260520044912.6751-1-devnexen@gmail.com
Fixes: 1cb9dc4b47 ("mm: hwpoison: support recovery from HugePage copy-on-write faults")
Signed-off-by: David Carlier <devnexen@gmail.com>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: yuehaibing <yuehaibing@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Carlier 2026-05-20 05:49:12 +01:00 committed by Andrew Morton
parent c0ca59beb5
commit 40c81856e6
1 changed files with 2 additions and 0 deletions
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2
mm/hugetlb.c
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@ -4977,6 +4977,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
addr, dst_vma);
folio_put(pte_folio);
if (ret) {
restore_reserve_on_error(h, dst_vma, addr, new_folio);
folio_put(new_folio);
break;
}
@ -6273,6 +6274,7 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
folio_put(*foliop);
*foliop = NULL;
if (ret) {
restore_reserve_on_error(h, dst_vma, dst_addr, folio);
folio_put(folio);
goto out;
}