Btrfs: Fix cache_block_group to catch holes at the start of the group

Cache block group was overly complex and missed free blocks at the very start
of the group.  This patch simplifies things significantly.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 33 insertions, 28 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index b074ad1416dd..9151850266b0 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -39,6 +39,7 @@ static int cache_block_group(struct btrfs_root *root,
         u64 i;
         u64 last = 0;
         u64 hole_size;
+        u64 first_free;
         int found = 0;
 
         root = root->fs_info->extent_root;
@@ -51,16 +52,22 @@ static int cache_block_group(struct btrfs_root *root,
         path = btrfs_alloc_path();
         if (!path)
                 return -ENOMEM;
+
         path->reada = 2;
+        first_free = block_group->key.objectid;
         key.objectid = block_group->key.objectid;
         key.flags = 0;
         key.offset = 0;
+
         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
         ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+
         if (ret < 0)
                 return ret;
+
         if (ret && path->slots[0] > 0)
                 path->slots[0]--;
+
         while(1) {
                 leaf = btrfs_buffer_leaf(path->nodes[0]);
                 slot = path->slots[0];
@@ -71,50 +78,48 @@ static int cache_block_group(struct btrfs_root *root,
                         if (ret == 0) {
                                 continue;
                         } else {
-                                if (found) {
-                                        hole_size = block_group->key.objectid +
-                                                block_group->key.offset - last;
-                                } else {
-                                        last = block_group->key.objectid;
-                                        hole_size = block_group->key.offset;
-                                }
-                                for (i = 0; i < hole_size; i++) {
-                                        set_radix_bit(extent_radix,
-                                                      last + i);
-                                }
                                 break;
                         }
                 }
+
                 btrfs_disk_key_to_cpu(&key, &leaf->items[slot].key);
+                if (key.objectid < block_group->key.objectid) {
+                        if (key.objectid + key.offset > first_free)
+                                first_free = key.objectid + key.offset;
+                        goto next;
+                }
+
                 if (key.objectid >= block_group->key.objectid +
                     block_group->key.offset) {
-                        if (found) {
-                                hole_size = block_group->key.objectid +
-                                        block_group->key.offset - last;
-                        } else {
-                                last = block_group->key.objectid;
-                                hole_size = block_group->key.offset;
-                        }
-                        for (i = 0; i < hole_size; i++) {
-                                set_radix_bit(extent_radix, last + i);
-                        }
                         break;
                 }
+
                 if (btrfs_key_type(&key) == BTRFS_EXTENT_ITEM_KEY) {
                         if (!found) {
-                                last = key.objectid + key.offset;
+                                last = first_free;
                                 found = 1;
-                        } else {
-                                hole_size = key.objectid - last;
-                                for (i = 0; i < hole_size; i++) {
-                                        set_radix_bit(extent_radix, last + i);
-                                }
-                                last = key.objectid + key.offset;
                         }
+                        hole_size = key.objectid - last;
+                        for (i = 0; i < hole_size; i++) {
+                                set_radix_bit(extent_radix, last + i);
+                        }
+                        last = key.objectid + key.offset;
                 }
+next:
                 path->slots[0]++;
         }
 
+        if (!found)
+                last = first_free;
+        if (block_group->key.objectid +
+            block_group->key.offset > last) {
+                hole_size = block_group->key.objectid +
+                        block_group->key.offset - last;
+                for (i = 0; i < hole_size; i++) {
+                        set_radix_bit(extent_radix,
+                                        last + i);
+                }
+        }
         block_group->cached = 1;
 err:
         btrfs_free_path(path);