Push lock_super() into the ->remount_fs() of filesystems that care about it

Note that since we can't run into contention between remount_fs and write_super
(due to exclusion on s_umount), we have to care only about filesystems that
touch lock_super() on their own.  Out of those ext3, ext4, hpfs, sysv and ufs
do need it; fat doesn't since its ->remount_fs() only accesses assign-once
data (basically, it's "we have no atime on directories and only have atime on
files for vfat; force nodiratime and possibly noatime into *flags").

[folded a build fix from hch]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 1d4180b..a9c6834 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3421,6 +3421,7 @@
 #endif
 
 	/* Store the original options */
+	lock_super(sb);
 	old_sb_flags = sb->s_flags;
 	old_opts.s_mount_opt = sbi->s_mount_opt;
 	old_opts.s_resuid = sbi->s_resuid;
@@ -3554,6 +3555,7 @@
 		    old_opts.s_qf_names[i] != sbi->s_qf_names[i])
 			kfree(old_opts.s_qf_names[i]);
 #endif
+	unlock_super(sb);
 	return 0;
 
 restore_opts:
@@ -3573,6 +3575,7 @@
 		sbi->s_qf_names[i] = old_opts.s_qf_names[i];
 	}
 #endif
+	unlock_super(sb);
 	return err;
 }