3 files changed, 66 insertions, 26 deletions

diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index cd42e30b7c6e..2189d3ffc85d 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -1,3 +1,8 @@
+#ifndef _LINUX_SWAPOPS_H
+#define _LINUX_SWAPOPS_H
+
+#include <linux/radix-tree.h>
+
 /*
  * swapcache pages are stored in the swapper_space radix tree.  We want to
  * get good packing density in that tree, so the index should be dense in
@@ -76,6 +81,22 @@ static inline pte_t swp_entry_to_pte(swp_entry_t entry)
         return __swp_entry_to_pte(arch_entry);
 }
 
+static inline swp_entry_t radix_to_swp_entry(void *arg)
+{
+        swp_entry_t entry;
+
+        entry.val = (unsigned long)arg >> RADIX_TREE_EXCEPTIONAL_SHIFT;
+        return entry;
+}
+
+static inline void *swp_to_radix_entry(swp_entry_t entry)
+{
+        unsigned long value;
+
+        value = entry.val << RADIX_TREE_EXCEPTIONAL_SHIFT;
+        return (void *)(value | RADIX_TREE_EXCEPTIONAL_ENTRY);
+}
+
 #ifdef CONFIG_MIGRATION
 static inline swp_entry_t make_migration_entry(struct page *page, int write)
 {
@@ -169,3 +190,5 @@ static inline int non_swap_entry(swp_entry_t entry)
         return 0;
 }
 #endif
+
+#endif /* _LINUX_SWAPOPS_H */
diff --git a/mm/filemap.c b/mm/filemap.c
index b83aebfd0a00..76bfb6460f57 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -714,9 +714,12 @@ repeat:
                 page = radix_tree_deref_slot(pagep);
                 if (unlikely(!page))
                         goto out;
-                if (radix_tree_deref_retry(page))
+                if (radix_tree_exception(page)) {
+                        if (radix_tree_exceptional_entry(page))
+                                goto out;
+                        /* radix_tree_deref_retry(page) */
                         goto repeat;
-
+                }
                 if (!page_cache_get_speculative(page))
                         goto repeat;
 
@@ -753,7 +756,7 @@ struct page *find_lock_page(struct address_space *mapping, pgoff_t offset)
 
 repeat:
         page = find_get_page(mapping, offset);
-        if (page) {
+        if (page && !radix_tree_exception(page)) {
                 lock_page(page);
                 /* Has the page been truncated? */
                 if (unlikely(page->mapping != mapping)) {
@@ -849,11 +852,14 @@ repeat:
                 if (unlikely(!page))
                         continue;
 
-                /*
-                 * This can only trigger when the entry at index 0 moves out
-                 * of or back to the root: none yet gotten, safe to restart.
-                 */
-                if (radix_tree_deref_retry(page)) {
+                if (radix_tree_exception(page)) {
+                        if (radix_tree_exceptional_entry(page))
+                                continue;
+                        /*
+                         * radix_tree_deref_retry(page):
+                         * can only trigger when entry at index 0 moves out of
+                         * or back to root: none yet gotten, safe to restart.
+                         */
                         WARN_ON(start | i);
                         goto restart;
                 }
@@ -912,12 +918,16 @@ repeat:
                 if (unlikely(!page))
                         continue;
 
-                /*
-                 * This can only trigger when the entry at index 0 moves out
-                 * of or back to the root: none yet gotten, safe to restart.
-                 */
-                if (radix_tree_deref_retry(page))
+                if (radix_tree_exception(page)) {
+                        if (radix_tree_exceptional_entry(page))
+                                break;
+                        /*
+                         * radix_tree_deref_retry(page):
+                         * can only trigger when entry at index 0 moves out of
+                         * or back to root: none yet gotten, safe to restart.
+                         */
                         goto restart;
+                }
 
                 if (!page_cache_get_speculative(page))
                         goto repeat;
@@ -977,12 +987,15 @@ repeat:
                 if (unlikely(!page))
                         continue;
 
-                /*
-                 * This can only trigger when the entry at index 0 moves out
-                 * of or back to the root: none yet gotten, safe to restart.
-                 */
-                if (radix_tree_deref_retry(page))
+                if (radix_tree_exception(page)) {
+                        BUG_ON(radix_tree_exceptional_entry(page));
+                        /*
+                         * radix_tree_deref_retry(page):
+                         * can only trigger when entry at index 0 moves out of
+                         * or back to root: none yet gotten, safe to restart.
+                         */
                         goto restart;
+                }
 
                 if (!page_cache_get_speculative(page))
                         goto repeat;
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 1b8c33907242..17bc224bce68 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 */