Btrfs: fix unlock after free on rewinded tree blocks

When tree_mod_log_rewind decides to make a copy of the current tree buffer
for its modifications, it subsequently freed the buffer before unlocking it.
Obviously, those operations are required in reverse order.

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

1 files changed, 11 insertions, 7 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index d7e0576038fb..c3c3d37f9c58 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1191,6 +1191,13 @@ __tree_mod_log_rewind(struct extent_buffer *eb, u64 time_seq,
         btrfs_set_header_nritems(eb, n);
 }
 
+/*
+ * Called with eb read locked. If the buffer cannot be rewinded, the same buffer
+ * is returned. If rewind operations happen, a fresh buffer is returned. The
+ * returned buffer is always read-locked. If the returned buffer is not the
+ * input buffer, the lock on the input buffer is released and the input buffer
+ * is freed (its refcount is decremented).
+ */
 static struct extent_buffer *
 tree_mod_log_rewind(struct btrfs_fs_info *fs_info, struct extent_buffer *eb,
                     u64 time_seq)
@@ -1224,8 +1231,11 @@ tree_mod_log_rewind(struct btrfs_fs_info *fs_info, struct extent_buffer *eb,
         }
 
         extent_buffer_get(eb_rewin);
+        btrfs_tree_read_unlock(eb);
         free_extent_buffer(eb);
 
+        extent_buffer_get(eb_rewin);
+        btrfs_tree_read_lock(eb_rewin);
         __tree_mod_log_rewind(eb_rewin, time_seq, tm);
         WARN_ON(btrfs_header_nritems(eb_rewin) >
                 BTRFS_NODEPTRS_PER_BLOCK(fs_info->tree_root));
@@ -2794,15 +2804,9 @@ again:
                                 btrfs_clear_path_blocking(p, b,
                                                           BTRFS_READ_LOCK);
                         }
+                        b = tree_mod_log_rewind(root->fs_info, b, time_seq);
                         p->locks[level] = BTRFS_READ_LOCK;
                         p->nodes[level] = b;
-                        b = tree_mod_log_rewind(root->fs_info, b, time_seq);
-                        if (b != p->nodes[level]) {
-                                btrfs_tree_unlock_rw(p->nodes[level],
-                                                     p->locks[level]);
-                                p->locks[level] = 0;
-                                p->nodes[level] = b;
-                        }
                 } else {
                         p->slots[level] = slot;
                         unlock_up(p, level, lowest_unlock, 0, NULL);