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

Neil Brown
2010-02-28T23:57:43Z

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;
> }