Btrfs: change how we track dirty roots

I've been overloading root->dirty_list to keep track of dirty roots and which
roots need to have their commit roots switched at transaction commit time.  This
could cause us to lose an update to the root which could corrupt the file
system.  To fix this use a state bit to know if the root is dirty, and if it
isn't set we go ahead and move the root to the dirty list.  This way if we
re-dirty the root after adding it to the switch_commit list we make sure to
update it.  This also makes it so that the extent root is always the last root
on the dirty list to try and keep the amount of churn down at this point in the
commit.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 12 insertions, 4 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 14a72ed14ef7b..97a98fc07cfcb 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -213,11 +213,19 @@ static struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root)
  */
 static void add_root_to_dirty_list(struct btrfs_root *root)
 {
+	if (test_bit(BTRFS_ROOT_DIRTY, &root->state) ||
+	    !test_bit(BTRFS_ROOT_TRACK_DIRTY, &root->state))
+		return;
+
 	spin_lock(&root->fs_info->trans_lock);
-	if (test_bit(BTRFS_ROOT_TRACK_DIRTY, &root->state) &&
-	    list_empty(&root->dirty_list)) {
-		list_add(&root->dirty_list,
-			 &root->fs_info->dirty_cowonly_roots);
+	if (!test_and_set_bit(BTRFS_ROOT_DIRTY, &root->state)) {
+		/* Want the extent tree to be the last on the list */
+		if (root->objectid == BTRFS_EXTENT_TREE_OBJECTID)
+			list_move_tail(&root->dirty_list,
+				       &root->fs_info->dirty_cowonly_roots);
+		else
+			list_move(&root->dirty_list,
+				  &root->fs_info->dirty_cowonly_roots);
 	}
 	spin_unlock(&root->fs_info->trans_lock);
 }