Btrfs: check for a null fs root when writing to the backup root log

During log replay, can commit the transaction before the fs_root
pointers are setup, so we have to make sure they are not null before
trying to use them.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index e532892431f4..e53a5bb85670 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1754,11 +1754,18 @@ static void backup_super_roots(struct btrfs_fs_info *info)
         btrfs_set_backup_extent_root_level(root_backup,
                                btrfs_header_level(info->extent_root->node));
 
-        btrfs_set_backup_fs_root(root_backup, info->fs_root->node->start);
-        btrfs_set_backup_fs_root_gen(root_backup,
+        /*
+         * we might commit during log recovery, which happens before we set
+         * the fs_root.  Make sure it is valid before we fill it in.
+         */
+        if (info->fs_root && info->fs_root->node) {
+                btrfs_set_backup_fs_root(root_backup,
+                                         info->fs_root->node->start);
+                btrfs_set_backup_fs_root_gen(root_backup,
                                btrfs_header_generation(info->fs_root->node));
-        btrfs_set_backup_fs_root_level(root_backup,
+                btrfs_set_backup_fs_root_level(root_backup,
                                btrfs_header_level(info->fs_root->node));
+        }
 
         btrfs_set_backup_dev_root(root_backup, info->dev_root->node->start);
         btrfs_set_backup_dev_root_gen(root_backup,