Btrfs: Simplify the logic in alloc_extent_buffer() for existing extent buffer case

alloc_extent_buffer() uses radix_tree_lookup() when radix_tree_insert()
fails with EEXIST. That part of the code is very similar to the code in
find_extent_buffer(). This patch replaces radix_tree_lookup() and
surrounding code in alloc_extent_buffer() with find_extent_buffer().

Note that radix_tree_lookup() does not need to be protected by
tree->buffer_lock. It is protected by eb->refs.

While at it, this patch
  - changes the other usage of radix_tree_lookup() in alloc_extent_buffer()
    with find_extent_buffer() to reduce redundancy.
  - removes the unused argument 'len' to find_extent_buffer().

Signed-Off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Reviewed-by: Zach Brown <zab@redhat.com>

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

1 files changed, 26 insertions, 37 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index c10291cc4fd1..5439f24ab06b 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4486,6 +4486,23 @@ static void mark_extent_buffer_accessed(struct extent_buffer *eb)
         }
 }
 
+struct extent_buffer *find_extent_buffer(struct extent_io_tree *tree,
+                                                        u64 start)
+{
+        struct extent_buffer *eb;
+
+        rcu_read_lock();
+        eb = radix_tree_lookup(&tree->buffer, start >> PAGE_CACHE_SHIFT);
+        if (eb && atomic_inc_not_zero(&eb->refs)) {
+                rcu_read_unlock();
+                mark_extent_buffer_accessed(eb);
+                return eb;
+        }
+        rcu_read_unlock();
+
+        return NULL;
+}
+
 struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
                                           u64 start, unsigned long len)
 {
@@ -4499,14 +4516,10 @@ struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
         int uptodate = 1;
         int ret;
 
-        rcu_read_lock();
-        eb = radix_tree_lookup(&tree->buffer, start >> PAGE_CACHE_SHIFT);
-        if (eb && atomic_inc_not_zero(&eb->refs)) {
-                rcu_read_unlock();
-                mark_extent_buffer_accessed(eb);
+
+        eb = find_extent_buffer(tree, start);
+        if (eb)
                 return eb;
-        }
-        rcu_read_unlock();
 
         eb = __alloc_extent_buffer(tree, start, len, GFP_NOFS);
         if (!eb)
@@ -4565,24 +4578,17 @@ again:
 
         spin_lock(&tree->buffer_lock);
         ret = radix_tree_insert(&tree->buffer, start >> PAGE_CACHE_SHIFT, eb);
+        spin_unlock(&tree->buffer_lock);
+        radix_tree_preload_end();
         if (ret == -EEXIST) {
-                exists = radix_tree_lookup(&tree->buffer,
-                                                start >> PAGE_CACHE_SHIFT);
-                if (!atomic_inc_not_zero(&exists->refs)) {
-                        spin_unlock(&tree->buffer_lock);
-                        radix_tree_preload_end();
-                        exists = NULL;
+                exists = find_extent_buffer(tree, start);
+                if (exists)
+                        goto free_eb;
+                else
                         goto again;
-                }
-                spin_unlock(&tree->buffer_lock);
-                radix_tree_preload_end();
-                mark_extent_buffer_accessed(exists);
-                goto free_eb;
         }
         /* add one reference for the tree */
         check_buffer_tree_ref(eb);
-        spin_unlock(&tree->buffer_lock);
-        radix_tree_preload_end();
 
         /*
          * there is a race where release page may have
@@ -4613,23 +4619,6 @@ free_eb:
         return exists;
 }
 
-struct extent_buffer *find_extent_buffer(struct extent_io_tree *tree,
-                                         u64 start, unsigned long len)
-{
-        struct extent_buffer *eb;
-
-        rcu_read_lock();
-        eb = radix_tree_lookup(&tree->buffer, start >> PAGE_CACHE_SHIFT);
-        if (eb && atomic_inc_not_zero(&eb->refs)) {
-                rcu_read_unlock();
-                mark_extent_buffer_accessed(eb);
-                return eb;
-        }
-        rcu_read_unlock();
-
-        return NULL;
-}
-
 static inline void btrfs_release_extent_buffer_rcu(struct rcu_head *head)
 {
         struct extent_buffer *eb =