6.11-stable review patch. If anyone has any objections, please let me know.
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From: Steve Sistare steven.sistare@oracle.com
commit c56b6f3d801d7ec8965993342bdd9e2972b6cb8e upstream.
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@... Fixes: 89c1905d9c14 ("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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/gup.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/mm/gup.c +++ b/mm/gup.c @@ -3618,7 +3618,7 @@ long memfd_pin_folios(struct file *memfd 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) @@ -3662,6 +3662,8 @@ long memfd_pin_folios(struct file *memfd &fbatch); if (folio) { folio_put(folio); + if (h) + folio_put(folio); folio = NULL; }