mm/hugetlb: simplify refs in memfd_alloc_folio

The folio_try_get in memfd_alloc_folio is not necessary.  Delete it, and
delete the matching folio_put in memfd_pin_folios.  This also avoids
leaking a ref if the memfd_alloc_folio call to hugetlb_add_to_page_cache
fails.  That error path is also broken in a second way -- when its
folio_put causes the ref to become 0, it will implicitly call
free_huge_folio, but then the path *explicitly* calls free_huge_folio. 
Delete the latter.

This is a continuation of the fix
  "mm/hugetlb: fix memfd_pin_folios free_huge_pages leak"

[[email protected]: remove explicit call to free_huge_folio(), per Matthew]
  Link: https://lkml.kernel.org/r/[email protected]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 89c1905 ("mm/gup: introduce memfd_pin_folios() for pinning memfd folios")
Signed-off-by: Steve Sistare <[email protected]>
Suggested-by: Vivek Kasireddy <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Steve Sistare

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 = NULL;
+	struct hstate *h;
 	long ret = -EINVAL;
 
 	if (start < 0 || start > end || !max_folios)
@@ -3659,8 +3659,6 @@ 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;
 			}
 

mm/memfd.c

@@ -89,13 +89,12 @@ struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
 						    numa_node_id(),
 						    NULL,
 						    gfp_mask);
-		if (folio && folio_try_get(folio)) {
+		if (folio) {
 			err = hugetlb_add_to_page_cache(folio,
 							memfd->f_mapping,
 							idx);
 			if (err) {
 				folio_put(folio);
-				free_huge_folio(folio);
 				return ERR_PTR(err);
 			}
 			folio_unlock(folio);