SUNRPC: Fix a UDP transport regression

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@altium.nl>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@vger.kernel.org [>= 3.1]

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
index cff40aa7db62..bf8c49ff7530 100644
--- 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);
@@ -281,6 +282,8 @@ void			xprt_connect(struct rpc_task *task);
 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);