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mm/hugetlb: fix memfd_pin_folios free_huge_pages leak

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memfd_pin_folios followed by unpin_folios fails to restore free_huge_pages
if the pages were not already faulted in, because the folio refcount for
pages created by memfd_alloc_folio never goes to 0.  memfd_pin_folios
needs another folio_put to undo the folio_try_get below:

memfd_alloc_folio()
  alloc_hugetlb_folio_nodemask()
    dequeue_hugetlb_folio_nodemask()
      dequeue_hugetlb_folio_node_exact()
        folio_ref_unfreeze(folio, 1);    ; adds 1 refcount
  folio_try_get()                        ; adds 1 refcount
  hugetlb_add_to_page_cache()            ; adds 512 refcount (on x86)

With the fix, after memfd_pin_folios + unpin_folios, the refcount for the
(unfaulted) page is 512, which is correct, as the refcount for a faulted
unpinned page is 513.

Link: https://lkml.kernel.org/r/1725373521-451395-3-git-send-email-steven.sistare@oracle.com
Fixes: 89c1905d9c ("mm/gup: introduce memfd_pin_folios() for pinning memfd folios")
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Acked-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Steve Sistare 2024-09-03 07:25:18 -07:00 committed by Andrew Morton
parent c225c4f605
commit c56b6f3d80
1 changed files with 3 additions and 1 deletions
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4
mm/gup.c
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@ -3615,7 +3615,7 @@ long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end,
pgoff_t start_idx, end_idx, next_idx;
struct folio *folio = NULL;
struct folio_batch fbatch;
struct hstate *h;
struct hstate *h = NULL;
long ret = -EINVAL;
if (start < 0 || start > end || !max_folios)
@ -3659,6 +3659,8 @@ long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end,
&fbatch);
if (folio) {
folio_put(folio);
if (h)
folio_put(folio);
folio = NULL;
}