mm: use radix_tree_iter_retry()

Instead of a 'goto restart', we can now use radix_tree_iter_retry() to
restart from our current position.  This will make a difference when
there are more ways to happen across an indirect pointer.  And it
eliminates some confusing gotos.

[vbabka@suse.cz: remove now-obsolete-and-misleading comment]
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 29 insertions, 47 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 084ad0fe73c7..7c00f105845e 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1255,7 +1255,6 @@ unsigned find_get_entries(struct address_space *mapping,
                 return 0;
 
         rcu_read_lock();
-restart:
         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
                 struct page *page;
 repeat:
@@ -1263,8 +1262,10 @@ repeat:
                 if (unlikely(!page))
                         continue;
                 if (radix_tree_exception(page)) {
-                        if (radix_tree_deref_retry(page))
-                                goto restart;
+                        if (radix_tree_deref_retry(page)) {
+                                slot = radix_tree_iter_retry(&iter);
+                                continue;
+                        }
                         /*
                          * A shadow entry of a recently evicted page, a swap
                          * entry from shmem/tmpfs or a DAX entry.  Return it
@@ -1317,7 +1318,6 @@ unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
                 return 0;
 
         rcu_read_lock();
-restart:
         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
                 struct page *page;
 repeat:
@@ -1327,13 +1327,8 @@ repeat:
 
                 if (radix_tree_exception(page)) {
                         if (radix_tree_deref_retry(page)) {
-                                /*
-                                 * Transient condition which can only trigger
-                                 * when entry at index 0 moves out of or back
-                                 * to root: none yet gotten, safe to restart.
-                                 */
-                                WARN_ON(iter.index);
-                                goto restart;
+                                slot = radix_tree_iter_retry(&iter);
+                                continue;
                         }
                         /*
                          * A shadow entry of a recently evicted page,
@@ -1384,7 +1379,6 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
                 return 0;
 
         rcu_read_lock();
-restart:
         radix_tree_for_each_contig(slot, &mapping->page_tree, &iter, index) {
                 struct page *page;
 repeat:
@@ -1395,12 +1389,8 @@ repeat:
 
                 if (radix_tree_exception(page)) {
                         if (radix_tree_deref_retry(page)) {
-                                /*
-                                 * Transient condition which can only trigger
-                                 * when entry at index 0 moves out of or back
-                                 * to root: none yet gotten, safe to restart.
-                                 */
-                                goto restart;
+                                slot = radix_tree_iter_retry(&iter);
+                                continue;
                         }
                         /*
                          * A shadow entry of a recently evicted page,
@@ -1460,7 +1450,6 @@ unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
                 return 0;
 
         rcu_read_lock();
-restart:
         radix_tree_for_each_tagged(slot, &mapping->page_tree,
                                    &iter, *index, tag) {
                 struct page *page;
@@ -1471,12 +1460,8 @@ repeat:
 
                 if (radix_tree_exception(page)) {
                         if (radix_tree_deref_retry(page)) {
-                                /*
-                                 * Transient condition which can only trigger
-                                 * when entry at index 0 moves out of or back
-                                 * to root: none yet gotten, safe to restart.
-                                 */
-                                goto restart;
+                                slot = radix_tree_iter_retry(&iter);
+                                continue;
                         }
                         /*
                          * A shadow entry of a recently evicted page.
@@ -1539,7 +1524,6 @@ unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
                 return 0;
 
         rcu_read_lock();
-restart:
         radix_tree_for_each_tagged(slot, &mapping->page_tree,
                                    &iter, start, tag) {
                 struct page *page;
@@ -1549,12 +1533,8 @@ repeat:
                         continue;
                 if (radix_tree_exception(page)) {
                         if (radix_tree_deref_retry(page)) {
-                                /*
-                                 * Transient condition which can only trigger
-                                 * when entry at index 0 moves out of or back
-                                 * to root: none yet gotten, safe to restart.
-                                 */
-                                goto restart;
+                                slot = radix_tree_iter_retry(&iter);
+                                continue;
                         }
 
                         /*
@@ -2171,10 +2151,11 @@ repeat:
                 if (unlikely(!page))
                         goto next;
                 if (radix_tree_exception(page)) {
-                        if (radix_tree_deref_retry(page))
-                                break;
-                        else
-                                goto next;
+                        if (radix_tree_deref_retry(page)) {
+                                slot = radix_tree_iter_retry(&iter);
+                                continue;
+                        }
+                        goto next;
                 }
 
                 if (!page_cache_get_speculative(page))
diff --git a/mm/shmem.c b/mm/shmem.c
index c484f6888d5e..91c0dadf48d3 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -383,13 +383,10 @@ restart:
 
                 page = radix_tree_deref_slot(slot);
 
-                /*
-                 * This should only be possible to happen at index 0, so we
-                 * don't need to reset the counter, nor do we risk infinite
-                 * restarts.
-                 */
-                if (radix_tree_deref_retry(page))
-                        goto restart;
+                if (radix_tree_deref_retry(page)) {
+                        slot = radix_tree_iter_retry(&iter);
+                        continue;
+                }
 
                 if (radix_tree_exceptional_entry(page))
                         swapped++;
@@ -1951,8 +1948,10 @@ restart:
         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
                 page = radix_tree_deref_slot(slot);
                 if (!page || radix_tree_exception(page)) {
-                        if (radix_tree_deref_retry(page))
-                                goto restart;
+                        if (radix_tree_deref_retry(page)) {
+                                slot = radix_tree_iter_retry(&iter);
+                                continue;
+                        }
                 } else if (page_count(page) - page_mapcount(page) > 1) {
                         spin_lock_irq(&mapping->tree_lock);
                         radix_tree_tag_set(&mapping->page_tree, iter.index,
@@ -2006,8 +2005,10 @@ restart:
 
                         page = radix_tree_deref_slot(slot);
                         if (radix_tree_exception(page)) {
-                                if (radix_tree_deref_retry(page))
-                                        goto restart;
+                                if (radix_tree_deref_retry(page)) {
+                                        slot = radix_tree_iter_retry(&iter);
+                                        continue;
+                                }
 
                                 page = NULL;
                         }