Re: The recent kref_put warning (was: [PATCH] sunrpc: remove unnecessary svc_xprt_put)

[Neil Brown <neilb@suse.de>]

On Sun, 28 Feb 2010 17:07:23 -0500
"J. Bruce Fields" <bfields@fieldses.org> wrote:

> On Sun, Feb 28, 2010 at 04:05:53PM -0500, J. Bruce Fields wrote:
> > On Sat, Feb 27, 2010 at 04:59:13PM +1100, Neil Brown wrote:
> > > I've made quite a few changes here - it might be worth splitting them
> > > up.
> > 
> > Probably so.
> 
> So, if I first revert b292cf9 and then b0401d7, I get the following.
> 
> I don't understand the "return 0" in the XPT_CLOSE case.  Is it really
> OK for the caller to try to process this request?

No, you are correct.  "return 0" is wrong, it should be "return -EAGAIN",
both in the XPT_CLOSE case and the XPT_LISTENER case.

I observed that in both those cases, 'len' remained at 0 and we didn't do
much else but 'return len', so I optimised.
I forgot to factor in:

	if (len == 0 || len == -EAGAIN) {
		rqstp->rq_res.len = 0;
		svc_xprt_release(rqstp);
		return -EAGAIN;
	}

So the svc_xprt_release needs to be moved in there as well, I'm not sure
about the rq_res.len = 0.
Maybe that was a bad case of premature-optimisation :-)

We should probably leave that last else clause as it is and just have a
single return from the function.

Thanks 
NeilBrown


> 
> --b.
> 
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index 8f0f1fb..48f91fb 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -706,9 +706,11 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
>  	spin_unlock_bh(&pool->sp_lock);
>  
>  	len = 0;
> +
>  	if (test_bit(XPT_CLOSE, &xprt->xpt_flags)) {
>  		dprintk("svc_recv: found XPT_CLOSE\n");
>  		svc_delete_xprt(xprt);
> +		return 0;
>  	} else if (test_bit(XPT_LISTENER, &xprt->xpt_flags)) {
>  		struct svc_xprt *newxpt;
>  		newxpt = xprt->xpt_ops->xpo_accept(xprt);
> @@ -735,19 +737,20 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
>  			svc_xprt_received(newxpt);
>  		}
>  		svc_xprt_received(xprt);
> -	} else {
> -		dprintk("svc: server %p, pool %u, transport %p, inuse=%d\n",
> -			rqstp, pool->sp_id, xprt,
> -			atomic_read(&xprt->xpt_ref.refcount));
> -		rqstp->rq_deferred = svc_deferred_dequeue(xprt);
> -		if (rqstp->rq_deferred) {
> -			svc_xprt_received(xprt);
> -			len = svc_deferred_recv(rqstp);
> -		} else
> -			len = xprt->xpt_ops->xpo_recvfrom(rqstp);
> -		dprintk("svc: got len=%d\n", len);
> +		return 0;
>  	}
>  
> +	dprintk("svc: server %p, pool %u, transport %p, inuse=%d\n",
> +		rqstp, pool->sp_id, xprt,
> +		atomic_read(&xprt->xpt_ref.refcount));
> +	rqstp->rq_deferred = svc_deferred_dequeue(xprt);
> +	if (rqstp->rq_deferred)
> +		len = svc_deferred_recv(rqstp);
> +	else
> +		len = xprt->xpt_ops->xpo_recvfrom(rqstp);
> +	dprintk("svc: got len=%d\n", len);
> +	svc_xprt_received(xprt);
> +
>  	/* No data, incomplete (TCP) read, or accept() */
>  	if (len == 0 || len == -EAGAIN) {
>  		rqstp->rq_res.len = 0;
> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
> index 9e09391..cc68137 100644
> --- a/net/sunrpc/svcsock.c
> +++ b/net/sunrpc/svcsock.c
> @@ -547,7 +547,6 @@ static int svc_udp_recvfrom(struct svc_rqst *rqstp)
>  			dprintk("svc: recvfrom returned error %d\n", -err);
>  			set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags);
>  		}
> -		svc_xprt_received(&svsk->sk_xprt);
>  		return -EAGAIN;
>  	}
>  	len = svc_addr_len(svc_addr(rqstp));
> @@ -562,11 +561,6 @@ static int svc_udp_recvfrom(struct svc_rqst *rqstp)
>  	svsk->sk_sk->sk_stamp = skb->tstamp;
>  	set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags); /* there may be more data... */
>  
> -	/*
> -	 * Maybe more packets - kick another thread ASAP.
> -	 */
> -	svc_xprt_received(&svsk->sk_xprt);
> -
>  	len  = skb->len - sizeof(struct udphdr);
>  	rqstp->rq_arg.len = len;
>  
> @@ -917,7 +911,6 @@ static int svc_tcp_recv_record(struct svc_sock *svsk, struct svc_rqst *rqstp)
>  		if (len < want) {
>  			dprintk("svc: short recvfrom while reading record "
>  				"length (%d of %d)\n", len, want);
> -			svc_xprt_received(&svsk->sk_xprt);
>  			goto err_again; /* record header not complete */
>  		}
>  
> @@ -953,7 +946,6 @@ static int svc_tcp_recv_record(struct svc_sock *svsk, struct svc_rqst *rqstp)
>  	if (len < svsk->sk_reclen) {
>  		dprintk("svc: incomplete TCP record (%d of %d)\n",
>  			len, svsk->sk_reclen);
> -		svc_xprt_received(&svsk->sk_xprt);
>  		goto err_again;	/* record not complete */
>  	}
>  	len = svsk->sk_reclen;
> @@ -961,10 +953,9 @@ static int svc_tcp_recv_record(struct svc_sock *svsk, struct svc_rqst *rqstp)
>  
>  	return len;
>   error:
> -	if (len == -EAGAIN) {
> +	if (len == -EAGAIN)
>  		dprintk("RPC: TCP recv_record got EAGAIN\n");
> -		svc_xprt_received(&svsk->sk_xprt);
> -	}
> +
>  	return len;
>   err_delete:
>  	set_bit(XPT_CLOSE, &svsk->sk_xprt.xpt_flags);
> @@ -1109,18 +1100,14 @@ out:
>  	svsk->sk_tcplen = 0;
>  
>  	svc_xprt_copy_addrs(rqstp, &svsk->sk_xprt);
> -	svc_xprt_received(&svsk->sk_xprt);
>  	if (serv->sv_stats)
>  		serv->sv_stats->nettcpcnt++;
>  
>  	return len;
>  
>  err_again:
> -	if (len == -EAGAIN) {
> +	if (len == -EAGAIN)
>  		dprintk("RPC: TCP recvfrom got EAGAIN\n");
> -		svc_xprt_received(&svsk->sk_xprt);
> -		return len;
> -	}
>  error:
>  	if (len != -EAGAIN) {
>  		printk(KERN_NOTICE "%s: recvfrom returned errno %d\n",
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> index f92e37e..0194de8 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> @@ -566,7 +566,6 @@ static int rdma_read_complete(struct svc_rqst *rqstp,
>  		ret, rqstp->rq_arg.len,	rqstp->rq_arg.head[0].iov_base,
>  		rqstp->rq_arg.head[0].iov_len);
>  
> -	svc_xprt_received(rqstp->rq_xprt);
>  	return ret;
>  }
>  
> @@ -665,7 +664,6 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
>  		rqstp->rq_arg.head[0].iov_len);
>  	rqstp->rq_prot = IPPROTO_MAX;
>  	svc_xprt_copy_addrs(rqstp, xprt);
> -	svc_xprt_received(xprt);
>  	return ret;
>  
>   close_out:
> @@ -678,6 +676,5 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
>  	 */
>  	set_bit(XPT_CLOSE, &xprt->xpt_flags);
>  defer:
> -	svc_xprt_received(xprt);
>  	return 0;
>  }