Re: [PATCH] fs/namespace: handle mount(MS_BIND|MS_REMOUNT) without locking sb->s_umount

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Wed, Mar 18, 2020 at 05:17:55PM +0300, Konstantin Khlebnikov wrote:
> @@ -459,11 +459,11 @@ void mnt_drop_write_file(struct file *file)
>  }
>  EXPORT_SYMBOL(mnt_drop_write_file);
>  
> +/* mount_lock must be held */
>  static int mnt_make_readonly(struct mount *mnt)
>  {
>  	int ret = 0;
>  
> -	lock_mount_hash();

I'd rather see
+	lockdep_assert_held_write(&mount_lock);
than a comment.  Maybe wrapped up into a macro like assert_hash_locked().