radix-tree,shmem: introduce radix_tree_iter_next()

shmem likes to occasionally drop the lock, schedule, then reacqire the
lock and continue with the iteration from the last place it left off.
This is currently done with a pretty ugly goto.  Introduce
radix_tree_iter_next() and use it throughout shmem.c.

[koct9i@gmail.com: fix bug in radix_tree_iter_next() for tagged iteration]
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 19 insertions, 9 deletions

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index b211f145c811..51a97ac8bfbf 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -403,6 +403,22 @@ void **radix_tree_iter_retry(struct radix_tree_iter *iter)
 }
 
 /**
+ * radix_tree_iter_next - resume iterating when the chunk may be invalid
+ * @iter:       iterator state
+ *
+ * If the iterator needs to release then reacquire a lock, the chunk may
+ * have been invalidated by an insertion or deletion.  Call this function
+ * to continue the iteration from the next index.
+ */
+static inline __must_check
+void **radix_tree_iter_next(struct radix_tree_iter *iter)
+{
+        iter->next_index = iter->index + 1;
+        iter->tags = 0;
+        return NULL;
+}
+
+/**
  * radix_tree_chunk_size - get current chunk size
  *
  * @iter:       pointer to radix tree iterator
diff --git a/mm/shmem.c b/mm/shmem.c
index 91c0dadf48d3..9428c51ab2d6 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -376,7 +376,6 @@ unsigned long shmem_partial_swap_usage(struct address_space *mapping,
 
         rcu_read_lock();
 
-restart:
         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
                 if (iter.index >= end)
                         break;
@@ -393,8 +392,7 @@ restart:
 
                 if (need_resched()) {
                         cond_resched_rcu();
-                        start = iter.index + 1;
-                        goto restart;
+                        slot = radix_tree_iter_next(&iter);
                 }
         }
 
@@ -1944,7 +1942,6 @@ static void shmem_tag_pins(struct address_space *mapping)
         start = 0;
         rcu_read_lock();
 
-restart:
         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
                 page = radix_tree_deref_slot(slot);
                 if (!page || radix_tree_exception(page)) {
@@ -1961,8 +1958,7 @@ restart:
 
                 if (need_resched()) {
                         cond_resched_rcu();
-                        start = iter.index + 1;
-                        goto restart;
+                        slot = radix_tree_iter_next(&iter);
                 }
         }
         rcu_read_unlock();
@@ -1999,7 +1995,6 @@ static int shmem_wait_for_pins(struct address_space *mapping)
 
                 start = 0;
                 rcu_read_lock();
-restart:
                 radix_tree_for_each_tagged(slot, &mapping->page_tree, &iter,
                                            start, SHMEM_TAG_PINNED) {
 
@@ -2033,8 +2028,7 @@ restart:
 continue_resched:
                         if (need_resched()) {
                                 cond_resched_rcu();
-                                start = iter.index + 1;
-                                goto restart;
+                                slot = radix_tree_iter_next(&iter);
                         }
                 }
                 rcu_read_unlock();