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>

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 2cde7b0a0106a2a34a337ae48a311e88f1838dad..50d7c99ddce77fe1fb1469275c46af8058c9c6b4 100644 (file)
--- 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);