From: Steve Sistare Date: Tue, 3 Sep 2024 14:25:18 +0000 (-0700) Subject: mm/hugetlb: fix memfd_pin_folios free_huge_pages leak X-Git-Tag: v6.12-rc1~26^2~15 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=c56b6f3d801d7ec8965993342bdd9e2972b6cb8e;p=thirdparty%2Fkernel%2Flinux.git mm/hugetlb: fix memfd_pin_folios free_huge_pages leak 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: 89c1905d9c14 ("mm/gup: introduce memfd_pin_folios() for pinning memfd folios") Signed-off-by: Steve Sistare Acked-by: Vivek Kasireddy Cc: David Hildenbrand Cc: Jason Gunthorpe Cc: Matthew Wilcox Cc: Muchun Song Cc: Peter Xu Cc: Signed-off-by: Andrew Morton --- diff --git a/mm/gup.c b/mm/gup.c index 8232c8c9c372b..3e7eac9a4f2b4 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -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; }