diff --git a/fs/nilfs2/cpfile.c b/fs/nilfs2/cpfile.c
index 1c6cfb5..3f5d5d0 100644
--- a/fs/nilfs2/cpfile.c
+++ b/fs/nilfs2/cpfile.c
@@ -871,7 +871,6 @@
 		 * exclusive with a new mount job.  Though it doesn't cover
 		 * umount, it's enough for the purpose.
 		 */
-		mutex_lock(&nilfs->ns_mount_mutex);
 		if (nilfs_checkpoint_is_mounted(nilfs, cno, 1)) {
 			/* Current implementation does not have to protect
 			   plain read-only mounts since they are exclusive
@@ -880,7 +879,6 @@
 			ret = -EBUSY;
 		} else
 			ret = nilfs_cpfile_clear_snapshot(cpfile, cno);
-		mutex_unlock(&nilfs->ns_mount_mutex);
 		return ret;
 	case NILFS_SNAPSHOT:
 		return nilfs_cpfile_set_snapshot(cpfile, cno);
diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
index d24057d..f6af760 100644
--- a/fs/nilfs2/ioctl.c
+++ b/fs/nilfs2/ioctl.c
@@ -99,7 +99,8 @@
 static int nilfs_ioctl_change_cpmode(struct inode *inode, struct file *filp,
 				     unsigned int cmd, void __user *argp)
 {
-	struct inode *cpfile = NILFS_SB(inode->i_sb)->s_nilfs->ns_cpfile;
+	struct the_nilfs *nilfs = NILFS_SB(inode->i_sb)->s_nilfs;
+	struct inode *cpfile = nilfs->ns_cpfile;
 	struct nilfs_transaction_info ti;
 	struct nilfs_cpmode cpmode;
 	int ret;
@@ -109,14 +110,17 @@
 	if (copy_from_user(&cpmode, argp, sizeof(cpmode)))
 		return -EFAULT;
 
+	mutex_lock(&nilfs->ns_mount_mutex);
 	nilfs_transaction_begin(inode->i_sb, &ti, 0);
 	ret = nilfs_cpfile_change_cpmode(
 		cpfile, cpmode.cm_cno, cpmode.cm_mode);
 	if (unlikely(ret < 0)) {
 		nilfs_transaction_abort(inode->i_sb);
+		mutex_unlock(&nilfs->ns_mount_mutex);
 		return ret;
 	}
 	nilfs_transaction_commit(inode->i_sb); /* never fails */
+	mutex_unlock(&nilfs->ns_mount_mutex);
 	return ret;
 }