Btrfs: fix accessing the root pointer in tree mod log functions

The tree mod log functions were accessing root->node->... directly, without
use of btrfs_root_node() or explicit rcu locking. This could lead to an
extent buffer reference being leaked and another reference being freed too
early when preemtion was enabled.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

1 files changed, 20 insertions, 20 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 1180209965db..d7e0576038fb 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1069,11 +1069,11 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,
  */
 static struct tree_mod_elem *
 __tree_mod_log_oldest_root(struct btrfs_fs_info *fs_info,
-                           struct btrfs_root *root, u64 time_seq)
+                           struct extent_buffer *eb_root, u64 time_seq)
 {
         struct tree_mod_elem *tm;
         struct tree_mod_elem *found = NULL;
-        u64 root_logical = root->node->start;
+        u64 root_logical = eb_root->start;
         int looped = 0;
 
         if (!time_seq)
@@ -1107,7 +1107,6 @@ __tree_mod_log_oldest_root(struct btrfs_fs_info *fs_info,
 
                 found = tm;
                 root_logical = tm->old_root.logical;
-                BUG_ON(root_logical == root->node->start);
                 looped = 1;
         }
 
@@ -1245,30 +1244,31 @@ static inline struct extent_buffer *
 get_old_root(struct btrfs_root *root, u64 time_seq)
 {
         struct tree_mod_elem *tm;
-        struct extent_buffer *eb;
+        struct extent_buffer *eb = NULL;
+        struct extent_buffer *eb_root;
         struct extent_buffer *old;
         struct tree_mod_root *old_root = NULL;
         u64 old_generation = 0;
         u64 logical;
         u32 blocksize;
 
-        eb = btrfs_read_lock_root_node(root);
-        tm = __tree_mod_log_oldest_root(root->fs_info, root, time_seq);
+        eb_root = btrfs_read_lock_root_node(root);
+        tm = __tree_mod_log_oldest_root(root->fs_info, eb_root, time_seq);
         if (!tm)
-                return root->node;
+                return eb_root;
 
         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;
+                logical = eb_root->start;
         }
 
         tm = tree_mod_log_search(root->fs_info, logical, time_seq);
         if (old_root && tm && tm->op != MOD_LOG_KEY_REMOVE_WHILE_FREEING) {
-                btrfs_tree_read_unlock(root->node);
-                free_extent_buffer(root->node);
+                btrfs_tree_read_unlock(eb_root);
+                free_extent_buffer(eb_root);
                 blocksize = btrfs_level_size(root, old_root->level);
                 old = read_tree_block(root, logical, blocksize, 0);
                 if (!old) {
@@ -1280,13 +1280,13 @@ get_old_root(struct btrfs_root *root, u64 time_seq)
                         free_extent_buffer(old);
                 }
         } else if (old_root) {
-                btrfs_tree_read_unlock(root->node);
-                free_extent_buffer(root->node);
+                btrfs_tree_read_unlock(eb_root);
+                free_extent_buffer(eb_root);
                 eb = alloc_dummy_extent_buffer(logical, root->nodesize);
         } else {
-                eb = btrfs_clone_extent_buffer(root->node);
-                btrfs_tree_read_unlock(root->node);
-                free_extent_buffer(root->node);
+                eb = btrfs_clone_extent_buffer(eb_root);
+                btrfs_tree_read_unlock(eb_root);
+                free_extent_buffer(eb_root);
         }
 
         if (!eb)
@@ -1296,7 +1296,7 @@ get_old_root(struct btrfs_root *root, u64 time_seq)
         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_owner(eb, btrfs_header_owner(eb_root));
                 btrfs_set_header_level(eb, old_root->level);
                 btrfs_set_header_generation(eb, old_generation);
         }
@@ -1313,15 +1313,15 @@ int btrfs_old_root_level(struct btrfs_root *root, u64 time_seq)
 {
         struct tree_mod_elem *tm;
         int level;
+        struct extent_buffer *eb_root = btrfs_root_node(root);
 
-        tm = __tree_mod_log_oldest_root(root->fs_info, root, time_seq);
+        tm = __tree_mod_log_oldest_root(root->fs_info, eb_root, time_seq);
         if (tm && tm->op == MOD_LOG_ROOT_REPLACE) {
                 level = tm->old_root.level;
         } else {
-                rcu_read_lock();
-                level = btrfs_header_level(root->node);
-                rcu_read_unlock();
+                level = btrfs_header_level(eb_root);
         }
+        free_extent_buffer(eb_root);
 
         return level;
 }