[PATCH 5/5] radix-tree,shmem: Introduce radix_tree_iter_next()

[Matthew Wilcox <matthew.r.wilcox@intel.com>]

From: Matthew Wilcox <willy@linux.intel.com>

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.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
---
 include/linux/radix-tree.h | 15 +++++++++++++++
 mm/shmem.c                 | 12 +++---------
 2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index db0ed595749b..dec2c6c77eea 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -403,6 +403,21 @@ 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;
+	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 6ec14b70d82d..438ea8004c26 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;
@@ -398,8 +397,7 @@ restart:
 
 		if (need_resched()) {
 			cond_resched_rcu();
-			start = iter.index + 1;
-			goto restart;
+			slot = radix_tree_iter_next(&iter);
 		}
 	}
 
@@ -1950,7 +1948,6 @@ 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)) {
@@ -1967,8 +1964,7 @@ restart:
 
 		if (need_resched()) {
 			cond_resched_rcu();
-			start = iter.index + 1;
-			goto restart;
+			slot = radix_tree_iter_next(&iter);
 		}
 	}
 	rcu_read_unlock();
@@ -2005,7 +2001,6 @@ 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) {
 
@@ -2039,8 +2034,7 @@ restart:
 continue_resched:
 			if (need_resched()) {
 				cond_resched_rcu();
-				start = iter.index + 1;
-				goto restart;
+				slot = radix_tree_iter_next(&iter);
 			}
 		}
 		rcu_read_unlock();
-- 
2.7.0.rc3