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Date: Fri, 28 Sep 2012 19:46:57 +0000
From: "Myklebust, Trond" <Trond.Myklebust@...app.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"stable@...r.kernel.org" <stable@...r.kernel.org>,
"alan@...rguk.ukuu.org.uk" <alan@...rguk.ukuu.org.uk>,
Dick Streefland <dick.streefland@...ium.nl>
Subject: Re: [ 089/262] SUNRPC: Fix a UDP transport regression
On Fri, 2012-09-28 at 11:50 -0700, Greg Kroah-Hartman wrote:
> From: Greg KH <gregkh@...uxfoundation.org>
>
> 3.5-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: Trond Myklebust <Trond.Myklebust@...app.com>
>
> commit f39c1bfb5a03e2d255451bff05be0d7255298fa4 upstream.
>
> Commit 43cedbf0e8dfb9c5610eb7985d5f21263e313802 (SUNRPC: Ensure that
> we grab the XPRT_LOCK before calling xprt_alloc_slot) is causing
> hangs in the case of NFS over UDP mounts.
>
> Since neither the UDP or the RDMA transport mechanism use dynamic slot
> allocation, we can skip grabbing the socket lock for those transports.
> Add a new rpc_xprt_op to allow switching between the TCP and UDP/RDMA
> case.
>
> Note that the NFSv4.1 back channel assigns the slot directly
> through rpc_run_bc_task, so we can ignore that case.
>
> Reported-by: Dick Streefland <dick.streefland@...ium.nl>
> Signed-off-by: Trond Myklebust <Trond.Myklebust@...app.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>
> ---
> include/linux/sunrpc/xprt.h | 3 +++
> net/sunrpc/xprt.c | 34 ++++++++++++++++++++--------------
> net/sunrpc/xprtrdma/transport.c | 1 +
> net/sunrpc/xprtsock.c | 3 +++
> 4 files changed, 27 insertions(+), 14 deletions(-)
>
> --- a/include/linux/sunrpc/xprt.h
> +++ b/include/linux/sunrpc/xprt.h
> @@ -114,6 +114,7 @@ struct rpc_xprt_ops {
> void (*set_buffer_size)(struct rpc_xprt *xprt, size_t sndsize, size_t rcvsize);
> int (*reserve_xprt)(struct rpc_xprt *xprt, struct rpc_task *task);
> void (*release_xprt)(struct rpc_xprt *xprt, struct rpc_task *task);
> + void (*alloc_slot)(struct rpc_xprt *xprt, struct rpc_task *task);
> void (*rpcbind)(struct rpc_task *task);
> void (*set_port)(struct rpc_xprt *xprt, unsigned short port);
> void (*connect)(struct rpc_task *task);
> @@ -279,6 +280,8 @@ void xprt_connect(struct rpc_task *tas
> void xprt_reserve(struct rpc_task *task);
> int xprt_reserve_xprt(struct rpc_xprt *xprt, struct rpc_task *task);
> int xprt_reserve_xprt_cong(struct rpc_xprt *xprt, struct rpc_task *task);
> +void xprt_alloc_slot(struct rpc_xprt *xprt, struct rpc_task *task);
> +void xprt_lock_and_alloc_slot(struct rpc_xprt *xprt, struct rpc_task *task);
> int xprt_prepare_transmit(struct rpc_task *task);
> void xprt_transmit(struct rpc_task *task);
> void xprt_end_transmit(struct rpc_task *task);
> --- a/net/sunrpc/xprt.c
> +++ b/net/sunrpc/xprt.c
> @@ -969,11 +969,11 @@ static bool xprt_dynamic_free_slot(struc
> return false;
> }
>
> -static void xprt_alloc_slot(struct rpc_task *task)
> +void xprt_alloc_slot(struct rpc_xprt *xprt, struct rpc_task *task)
> {
> - struct rpc_xprt *xprt = task->tk_xprt;
> struct rpc_rqst *req;
>
> + spin_lock(&xprt->reserve_lock);
> if (!list_empty(&xprt->free)) {
> req = list_entry(xprt->free.next, struct rpc_rqst, rq_list);
> list_del(&req->rq_list);
> @@ -994,12 +994,29 @@ static void xprt_alloc_slot(struct rpc_t
> default:
> task->tk_status = -EAGAIN;
> }
> + spin_unlock(&xprt->reserve_lock);
> return;
> out_init_req:
> task->tk_status = 0;
> task->tk_rqstp = req;
> xprt_request_init(task, xprt);
> + spin_unlock(&xprt->reserve_lock);
> +}
> +EXPORT_SYMBOL_GPL(xprt_alloc_slot);
> +
> +void xprt_lock_and_alloc_slot(struct rpc_xprt *xprt, struct rpc_task *task)
> +{
> + /* Note: grabbing the xprt_lock_write() ensures that we throttle
> + * new slot allocation if the transport is congested (i.e. when
> + * reconnecting a stream transport or when out of socket write
> + * buffer space).
> + */
> + if (xprt_lock_write(xprt, task)) {
> + xprt_alloc_slot(xprt, task);
> + xprt_release_write(xprt, task);
> + }
> }
> +EXPORT_SYMBOL_GPL(xprt_lock_and_alloc_slot);
>
> static void xprt_free_slot(struct rpc_xprt *xprt, struct rpc_rqst *req)
> {
> @@ -1083,20 +1100,9 @@ void xprt_reserve(struct rpc_task *task)
> if (task->tk_rqstp != NULL)
> return;
>
> - /* Note: grabbing the xprt_lock_write() here is not strictly needed,
> - * but ensures that we throttle new slot allocation if the transport
> - * is congested (e.g. if reconnecting or if we're out of socket
> - * write buffer space).
> - */
> task->tk_timeout = 0;
> task->tk_status = -EAGAIN;
> - if (!xprt_lock_write(xprt, task))
> - return;
> -
> - spin_lock(&xprt->reserve_lock);
> - xprt_alloc_slot(task);
> - spin_unlock(&xprt->reserve_lock);
> - xprt_release_write(xprt, task);
> + xprt->ops->alloc_slot(xprt, task);
> }
>
> static inline __be32 xprt_alloc_xid(struct rpc_xprt *xprt)
> --- a/net/sunrpc/xprtrdma/transport.c
> +++ b/net/sunrpc/xprtrdma/transport.c
> @@ -713,6 +713,7 @@ static void xprt_rdma_print_stats(struct
> static struct rpc_xprt_ops xprt_rdma_procs = {
> .reserve_xprt = xprt_rdma_reserve_xprt,
> .release_xprt = xprt_release_xprt_cong, /* sunrpc/xprt.c */
> + .alloc_slot = xprt_alloc_slot,
> .release_request = xprt_release_rqst_cong, /* ditto */
> .set_retrans_timeout = xprt_set_retrans_timeout_def, /* ditto */
> .rpcbind = rpcb_getport_async, /* sunrpc/rpcb_clnt.c */
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -2433,6 +2433,7 @@ static void bc_destroy(struct rpc_xprt *
> static struct rpc_xprt_ops xs_local_ops = {
> .reserve_xprt = xprt_reserve_xprt,
> .release_xprt = xs_tcp_release_xprt,
> + .alloc_slot = xprt_alloc_slot,
> .rpcbind = xs_local_rpcbind,
> .set_port = xs_local_set_port,
> .connect = xs_connect,
> @@ -2449,6 +2450,7 @@ static struct rpc_xprt_ops xs_udp_ops =
> .set_buffer_size = xs_udp_set_buffer_size,
> .reserve_xprt = xprt_reserve_xprt_cong,
> .release_xprt = xprt_release_xprt_cong,
> + .alloc_slot = xprt_alloc_slot,
> .rpcbind = rpcb_getport_async,
> .set_port = xs_set_port,
> .connect = xs_connect,
> @@ -2466,6 +2468,7 @@ static struct rpc_xprt_ops xs_udp_ops =
> static struct rpc_xprt_ops xs_tcp_ops = {
> .reserve_xprt = xprt_reserve_xprt,
> .release_xprt = xs_tcp_release_xprt,
> + .alloc_slot = xprt_lock_and_alloc_slot,
> .rpcbind = rpcb_getport_async,
> .set_port = xs_set_port,
> .connect = xs_connect,
>
>
Hi Greg,
Can we please hold on this one for now. It appears that it requires an
extra initialiser in the 'bc_tcp_ops' declaration in
net/sunrpc/xprtsock.c (to set '.alloc_slot = xprt_alloc_slot').
I have a separate patch for that, but it has not yet made it upstream.
Cheers
Trond
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@...app.com
www.netapp.com
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