linux-kernel - Re: [PATCH 3/6] ksmbd: replace rwlock with rcu for concurrenct access on conn list

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Message-ID: <Y9dEZ5IgfwpZNlVm@google.com>
Date:   Mon, 30 Jan 2023 13:15:35 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Dawei Li <set_pte_at@...look.com>
Cc:     linkinjeon@...nel.org, sfrench@...ba.org, senozhatsky@...omium.org,
        tom@...pey.com, hyc.lee@...il.com, linux-cifs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] ksmbd: replace rwlock with rcu for concurrenct
 access on conn list

On (23/01/15 18:32), Dawei Li wrote:
> 
>  void ksmbd_conn_free(struct ksmbd_conn *conn)
>  {
> -	write_lock(&conn_list_lock);
> -	list_del(&conn->conns_list);
> -	write_unlock(&conn_list_lock);
> +	spin_lock(&conn_list_lock);
> +	list_del_rcu(&conn->conns_list);
> +	spin_unlock(&conn_list_lock);
>  
>  	xa_destroy(&conn->sessions);
>  	kvfree(conn->request_buf);

>From a quick look this does not seem like a correct RCU usage. E.g.
where do you wait for grace periods and synchronize readers/writers?