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

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Message-ID: <TYCP286MB23230E29CC81F5C0590C59C9CAD39@TYCP286MB2323.JPNP286.PROD.OUTLOOK.COM>
Date:   Mon, 30 Jan 2023 22:16:37 +0800
From:   Dawei Li <set_pte_at@...look.com>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     linkinjeon@...nel.org, sfrench@...ba.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

Hi Sergey,

Thanks for reviewing,

On Mon, Jan 30, 2023 at 01:15:35PM +0900, Sergey Senozhatsky wrote:
> 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);
        synchronize_rcu(); 
> >  
> >  	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?

Nice catch, I totally mess it up. Thanks!

At first glance, I assume synchronize_rcu() will do the job if sleeping
is OK?

Steve, Namjae,
Please drop this buggy patch from ksmbd-for-next.

Thanks,
     Dawei