1 files changed, 12 insertions, 8 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 1b8c3390724..17bc224bce6 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1924,20 +1924,24 @@ static unsigned long read_swap_header(struct swap_info_struct *p,
 
         /*
          * Find out how many pages are allowed for a single swap
-         * device. There are two limiting factors: 1) the number of
-         * bits for the swap offset in the swp_entry_t type and
-         * 2) the number of bits in the a swap pte as defined by
-         * the different architectures. In order to find the
-         * largest possible bit mask a swap entry with swap type 0
+         * device. There are three limiting factors: 1) the number
+         * of bits for the swap offset in the swp_entry_t type, and
+         * 2) the number of bits in the swap pte as defined by the
+         * the different architectures, and 3) the number of free bits
+         * in an exceptional radix_tree entry. In order to find the
+         * largest possible bit mask, a swap entry with swap type 0
          * and swap offset ~0UL is created, encoded to a swap pte,
-         * decoded to a swp_entry_t again and finally the swap
+         * decoded to a swp_entry_t again, and finally the swap
          * offset is extracted. This will mask all the bits from
          * the initial ~0UL mask that can't be encoded in either
          * the swp_entry_t or the architecture definition of a
-         * swap pte.
+         * swap pte.  Then the same is done for a radix_tree entry.
          */
         maxpages = swp_offset(pte_to_swp_entry(
-                        swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
+                        swp_entry_to_pte(swp_entry(0, ~0UL))));
+        maxpages = swp_offset(radix_to_swp_entry(
+                        swp_to_radix_entry(swp_entry(0, maxpages)))) + 1;
+
         if (maxpages > swap_header->info.last_page) {
                 maxpages = swap_header->info.last_page + 1;
                 /* p->max is an unsigned int: don't overflow it */