ext2 reservations: fix for r/o bind mounts: take-writer-count

diff -puN fs/ext2/ioctl.c~ext2-reservations-take-writer-count fs/ext2/ioctl.c
@@ -107,18 +107,21 @@ setflags_out:
 		}
 		return -ENOTTY;
 	case EXT2_IOC_SETRSVSZ: {
-
+		int ret;
 		if (!test_opt(inode->i_sb, RESERVATION) ||!S_ISREG(inode->i_mode))
 			return -ENOTTY;
 
-		if (IS_RDONLY(inode))
-			return -EROFS;
+		ret = mnt_want_write(filp->f_vfsmnt);
+		if (ret)
+			return ret;
 
+		ret = -EACCES;
 		if ((current->fsuid != inode->i_uid) && !capable(CAP_FOWNER))
-			return -EACCES;
+			goto setrsvsz_out;
 
+		ret = -EFAULT;
 		if (get_user(rsv_window_size, (int __user *)arg))
-			return -EFAULT;
+			goto setrsvsz_out;
 
 		if (rsv_window_size > EXT2_MAX_RESERVE_BLOCKS)
 			rsv_window_size = EXT2_MAX_RESERVE_BLOCKS;

@@ -140,7 +143,9 @@ setflags_out:
 			rsv->rsv_goal_size = rsv_window_size;
 		}
 		mutex_unlock(&ei->truncate_mutex);
-		return 0;
+	setrsvsz_out:
+		mnt_drop_write(filp->f_vfsmnt);
+		return ret;
 	}
 	default:
 		return -ENOTTY;