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Date:   Tue, 18 Jul 2023 09:26:59 -0400
From:   Chuck Lever <cel@kernel.org>
To:     NeilBrown <neilb@suse.de>
Cc:     Chuck Lever <chuck.lever@oracle.com>,
        Jeff Layton <jlayton@kernel.org>, linux-nfs@vger.kernel.org
Subject: Re: [PATCH 04/14] SUNRPC: change svc_recv() to return void.
Message-ID: <ZLaTI8f4FU/b1Lj3@bazille.1015granger.net>
References: <168966227838.11075.2974227708495338626.stgit@noble.brown>
 <168966228862.11075.10086063375287695723.stgit@noble.brown>
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On Tue, Jul 18, 2023 at 04:38:08PM +1000, NeilBrown wrote:
> svc_recv() currently returns a 0 on success or one of two errors:
>  - -EAGAIN means no message was successfully received
>  - -EINTR means the thread has been told to stop
> 
> Previously nfsd would stop as the result of a signal as well as
> following kthread_stop().  In that case the difference was useful: EINTR
> means stop unconditionally.  EAGAIN means stop if kthread_should_stop(),
> continue otherwise.
> 
> Now threads only exit when kthread_should_stop() so we don't need the
> distinction.
> 
> So have all threads test kthread_should_stop() (most do), and return
> simple success/failure from svc_recv().

The above sentence doesn't make sense. svc_recv() now returns void,
not success/failure.


> Also change some helpers that svc_recv() uses to not bother with an
> error code, returning a bool in once case, and NULL for failure in
> another.
> 
> Signed-off-by: NeilBrown <neilb@suse.de>
> ---
>  fs/lockd/svc.c                 |    9 +++------
>  fs/nfs/callback.c              |    5 +----
>  fs/nfsd/nfssvc.c               |    8 ++------
>  include/linux/sunrpc/svcsock.h |    2 +-
>  net/sunrpc/svc_xprt.c          |   27 +++++++++++----------------
>  5 files changed, 18 insertions(+), 33 deletions(-)
> 
> diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
> index 91ef139a7757..a43b63e46127 100644
> --- a/fs/lockd/svc.c
> +++ b/fs/lockd/svc.c
> @@ -116,7 +116,6 @@ static void set_grace_period(struct net *net)
>  static int
>  lockd(void *vrqstp)
>  {
> -	int		err = 0;
>  	struct svc_rqst *rqstp = vrqstp;
>  	struct net *net = &init_net;
>  	struct lockd_net *ln = net_generic(net, lockd_net_id);
> @@ -139,12 +138,10 @@ lockd(void *vrqstp)
>  		timeout = nlmsvc_retry_blocked();
>  
>  		/*
> -		 * Find a socket with data available and call its
> -		 * recvfrom routine.
> +		 * Find any work to do, such as a socket with data available,
> +		 * and do the work.
>  		 */
> -		err = svc_recv(rqstp, timeout);
> -		if (err == -EAGAIN || err == -EINTR)
> -			continue;
> +		svc_recv(rqstp, timeout);
>  	}
>  	if (nlmsvc_ops)
>  		nlmsvc_invalidate_all();
> diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
> index 2d94384bd6a9..914d2402ca98 100644
> --- a/fs/nfs/callback.c
> +++ b/fs/nfs/callback.c
> @@ -74,7 +74,6 @@ static int nfs4_callback_up_net(struct svc_serv *serv, struct net *net)
>  static int
>  nfs4_callback_svc(void *vrqstp)
>  {
> -	int err;
>  	struct svc_rqst *rqstp = vrqstp;
>  
>  	set_freezable();
> @@ -83,9 +82,7 @@ nfs4_callback_svc(void *vrqstp)
>  		/*
>  		 * Listen for a request on the socket
>  		 */
> -		err = svc_recv(rqstp, MAX_SCHEDULE_TIMEOUT);
> -		if (err == -EAGAIN || err == -EINTR)
> -			continue;
> +		svc_recv(rqstp, MAX_SCHEDULE_TIMEOUT);
>  	}
>  
>  	svc_exit_thread(rqstp);
> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> index 3e08cc746870..5bf48c33986e 100644
> --- a/fs/nfsd/nfssvc.c
> +++ b/fs/nfsd/nfssvc.c
> @@ -953,7 +953,6 @@ nfsd(void *vrqstp)
>  	struct svc_xprt *perm_sock = list_entry(rqstp->rq_server->sv_permsocks.next, typeof(struct svc_xprt), xpt_list);
>  	struct net *net = perm_sock->xpt_net;
>  	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
> -	int err;
>  
>  	/* At this point, the thread shares current->fs
>  	 * with the init process. We need to create files with the
> @@ -972,7 +971,7 @@ nfsd(void *vrqstp)
>  	/*
>  	 * The main request loop
>  	 */
> -	for (;;) {
> +	while (!kthread_should_stop()) {
>  		/* Update sv_maxconn if it has changed */
>  		rqstp->rq_server->sv_maxconn = nn->max_connections;
>  
> @@ -980,10 +979,7 @@ nfsd(void *vrqstp)
>  		 * Find a socket with data available and call its
>  		 * recvfrom routine.
>  		 */
> -		while ((err = svc_recv(rqstp, 60*60*HZ)) == -EAGAIN)
> -			;
> -		if (err == -EINTR)
> -			break;
> +		svc_recv(rqstp, 60*60*HZ);
>  		validate_process_creds();
>  	}
>  
> diff --git a/include/linux/sunrpc/svcsock.h b/include/linux/sunrpc/svcsock.h
> index 55446136499f..fb5c98069356 100644
> --- a/include/linux/sunrpc/svcsock.h
> +++ b/include/linux/sunrpc/svcsock.h
> @@ -64,7 +64,7 @@ static inline u32 svc_sock_final_rec(struct svc_sock *svsk)
>   * Function prototypes.
>   */
>  void		svc_close_net(struct svc_serv *, struct net *);
> -int		svc_recv(struct svc_rqst *, long);
> +void		svc_recv(struct svc_rqst *, long);
>  void		svc_send(struct svc_rqst *rqstp);
>  void		svc_drop(struct svc_rqst *);
>  void		svc_sock_update_bufs(struct svc_serv *serv);
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index c808f6d60c99..67825eef8646 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -664,7 +664,7 @@ static void svc_check_conn_limits(struct svc_serv *serv)
>  	}
>  }
>  
> -static int svc_alloc_arg(struct svc_rqst *rqstp)
> +static bool svc_alloc_arg(struct svc_rqst *rqstp)
>  {
>  	struct svc_serv *serv = rqstp->rq_server;
>  	struct xdr_buf *arg = &rqstp->rq_arg;
> @@ -689,7 +689,7 @@ static int svc_alloc_arg(struct svc_rqst *rqstp)
>  		set_current_state(TASK_IDLE);
>  		if (kthread_should_stop()) {
>  			set_current_state(TASK_RUNNING);
> -			return -EINTR;
> +			return false;
>  		}
>  		trace_svc_alloc_arg_err(pages, ret);
>  		memalloc_retry_wait(GFP_KERNEL);
> @@ -708,7 +708,7 @@ static int svc_alloc_arg(struct svc_rqst *rqstp)
>  	arg->tail[0].iov_len = 0;
>  
>  	rqstp->rq_xid = xdr_zero;
> -	return 0;
> +	return true;
>  }
>  
>  static bool
> @@ -773,9 +773,9 @@ static struct svc_xprt *svc_get_next_xprt(struct svc_rqst *rqstp, long timeout)
>  	if (!time_left)
>  		percpu_counter_inc(&pool->sp_threads_timedout);
>  	if (kthread_should_stop())
> -		return ERR_PTR(-EINTR);
> +		return NULL;
>  	percpu_counter_inc(&pool->sp_threads_no_work);
> -	return ERR_PTR(-EAGAIN);
> +	return NULL;
>  out_found:
>  	/* Normally we will wait up to 5 seconds for any required
>  	 * cache information to be provided.
> @@ -856,32 +856,27 @@ static int svc_handle_xprt(struct svc_rqst *rqstp, struct svc_xprt *xprt)
>   * organised not to touch any cachelines in the shared svc_serv
>   * structure, only cachelines in the local svc_pool.
>   */
> -int svc_recv(struct svc_rqst *rqstp, long timeout)
> +void svc_recv(struct svc_rqst *rqstp, long timeout)
>  {
>  	struct svc_xprt		*xprt = NULL;
>  	struct svc_serv		*serv = rqstp->rq_server;
> -	int			len, err;
> +	int			len;
>  
> -	err = svc_alloc_arg(rqstp);
> -	if (err)
> +	if (!svc_alloc_arg(rqstp))
>  		goto out;
>  
>  	try_to_freeze();
>  	cond_resched();
> -	err = -EINTR;
>  	if (kthread_should_stop())
>  		goto out;
>  
>  	xprt = svc_get_next_xprt(rqstp, timeout);
> -	if (IS_ERR(xprt)) {
> -		err = PTR_ERR(xprt);
> +	if (!xprt)
>  		goto out;
> -	}
>  
>  	len = svc_handle_xprt(rqstp, xprt);
>  
>  	/* No data, incomplete (TCP) read, or accept() */
> -	err = -EAGAIN;
>  	if (len <= 0)
>  		goto out_release;
>  
> @@ -896,12 +891,12 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
>  	percpu_counter_inc(&rqstp->rq_pool->sp_messages_arrived);
>  	rqstp->rq_stime = ktime_get();
>  	svc_process(rqstp);
> -	return 0;
> +	return;
>  out_release:
>  	rqstp->rq_res.len = 0;
>  	svc_xprt_release(rqstp);
>  out:
> -	return err;
> +	return;
>  }
>  EXPORT_SYMBOL_GPL(svc_recv);
>  
> 
>