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

J. Bruce Fields
2010-04-28T21:43:21Z

On Mon, Mar 01, 2010 at 04:51:14PM +1100, Neil Brown wrote:
> On Sun, 28 Feb 2010 22:46:47 -0500
> "J. Bruce Fields" <bfields@fieldses.org> wrote:
> > I also agree with the cleanup that moves the svc_xprt_received to one
> > place, I'm just hoping you won't mind regenerating it against this.
>
> See below.
> There is still room to tidy up svc_recv, including getting the xpo_recvfrom
> routines to report -EAGAIN when that is what they mean, rather than '0',
> but I'm not really happy with what I have so-far so I won't post it yet.

I've applied this for 2.6.35; apologies for the delay.

Did you get another chance to look the further cleanup you were
considering?

--b.

>
> NeilBrown
>
>
> From 1e75b9d1232957cd44e0d8ea704c9af431cc85be Mon Sep 17 00:00:00 2001
> From: NeilBrown <neilb@suse.de>
> Date: Mon, 1 Mar 2010 15:49:11 +1100
> Subject: [PATCH] sunrpc: centralise most calls to svc_xprt_received
>
> svc_xprt_received must be called when ->xpo_recvfrom has finished
> receiving a message, so that the XPT_BUSY flag will be cleared and
> if necessary, requeued for further work.
>
> This call is currently made in each ->xpo_recvfrom function, often
> from multiple different point, in each case it is the earliest point
> on a particular path where it is known that the protection provided by
> XPT_BUSY is no longer needed.
>
> However there are (still) some error paths which do not call
> svc_xprt_received, and requiring each ->xpo_recvfrom to make the call
> does not encourage robustness.
>
> So: move the svc_xprt_received call to be made just after the
> call to ->xpo_recvfrom(), and move it of the various ->xpo_recvfrom
> methods.
>
> This means that it may not be called at the earliest possible instant,
> but this is unlikely to be a measurable performance issue.
>
> Note that there are still other calls to svc_xprt_received as it is
> also needed when an xprt is newly created.
>
> Signed-off-by: NeilBrown <neilb@suse.de>
>
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index 6bd41a9..70b74be 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -736,8 +736,10 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
> if (rqstp->rq_deferred) {
> svc_xprt_received(xprt);
> len = svc_deferred_recv(rqstp);
> - } else
> + } else {
> len = xprt->xpt_ops->xpo_recvfrom(rqstp);
> + svc_xprt_received(xprt);
> + }
> dprintk("svc: got len=%d\n", len);
> }
>
> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
> index 528efef..7425029 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;
> @@ -961,14 +953,11 @@ 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);
> - svc_xprt_received(&svsk->sk_xprt);
> err_again:
> return -EAGAIN;
> }
> @@ -1110,7 +1099,6 @@ 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++;
>
> @@ -1119,7 +1107,6 @@ out:
> err_again:
> if (len == -EAGAIN) {
> dprintk("RPC: TCP recvfrom got EAGAIN\n");
> - svc_xprt_received(&svsk->sk_xprt);
> return len;
> }
> error:
> 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;
> }