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

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 1cb9dc4b475c
("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: 1cb9dc4b475c ("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>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ece86d9339cebc0d5c8cadd16fc1d39f5cad634f..1b1d4f87a3a4c9f6d08cd4229b48361759d514a1 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4977,6 +4977,7 @@ again:
                                                            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;
                }