Btrfs: fix return value for __tree_mod_log_oldest_root

In __tree_mod_log_oldest_root() we must return the found operation even if
it's not a ROOT_REPLACE operation. Otherwise, the caller assumes that there
are no operations to be rewinded and returns immediately.

The code in the caller is modified to improve readability.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>

1 files changed, 20 insertions, 13 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 2cde7b0a0106..50d7c99ddce7 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1023,6 +1023,10 @@ __tree_mod_log_oldest_root(struct btrfs_fs_info *fs_info,
                 looped = 1;
         }
 
+        /* if there's no old root to return, return what we found instead */
+        if (!found)
+                found = tm;
+
         return found;
 }
 
@@ -1155,18 +1159,24 @@ get_old_root(struct btrfs_root *root, u64 time_seq)
 {
         struct tree_mod_elem *tm;
         struct extent_buffer *eb;
-        struct tree_mod_root *old_root;
+        struct tree_mod_root *old_root = NULL;
         u64 old_generation;
+        u64 logical;
 
         eb = btrfs_read_lock_root_node(root);
         tm = __tree_mod_log_oldest_root(root->fs_info, root, time_seq);
         if (!tm)
                 return root->node;
 
-        old_root = &tm->old_root;
-        old_generation = tm->generation;
+        if (tm->op == MOD_LOG_ROOT_REPLACE) {
+                old_root = &tm->old_root;
+                old_generation = tm->generation;
+                logical = old_root->logical;
+        } else {
+                logical = root->node->start;
+        }
 
-        tm = tree_mod_log_search(root->fs_info, old_root->logical, time_seq);
+        tm = tree_mod_log_search(root->fs_info, logical, time_seq);
         /*
          * there was an item in the log when __tree_mod_log_oldest_root
          * returned. this one must not go away, because the time_seq passed to
@@ -1174,26 +1184,23 @@ get_old_root(struct btrfs_root *root, u64 time_seq)
          */
         BUG_ON(!tm);
 
-        if (old_root->logical == root->node->start) {
-                /* there are logged operations for the current root */
-                eb = btrfs_clone_extent_buffer(root->node);
-        } else {
-                /* there's a root replace operation for the current root */
+        if (old_root)
                 eb = alloc_dummy_extent_buffer(tm->index << PAGE_CACHE_SHIFT,
                                                root->nodesize);
-        }
+        else
+                eb = btrfs_clone_extent_buffer(root->node);
         btrfs_tree_read_unlock(root->node);
         free_extent_buffer(root->node);
         if (!eb)
                 return NULL;
         btrfs_tree_read_lock(eb);
-        if (old_root->logical != root->node->start) {
+        if (old_root) {
                 btrfs_set_header_bytenr(eb, eb->start);
                 btrfs_set_header_backref_rev(eb, BTRFS_MIXED_BACKREF_REV);
                 btrfs_set_header_owner(eb, root->root_key.objectid);
+                btrfs_set_header_level(eb, old_root->level);
+                btrfs_set_header_generation(eb, old_generation);
         }
-        btrfs_set_header_level(eb, old_root->level);
-        btrfs_set_header_generation(eb, old_generation);
         __tree_mod_log_rewind(eb, time_seq, tm);
         extent_buffer_get(eb);