SUNRPC: Fix a UDP transport regression

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@altium.nl>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
index 15518a152ac3db6e973a95685d50d200e6a1f475..0a4cd1093c09eb6c692ffec031d0bcd703df8590 100644 (file)
--- 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);
@@ -274,6 +275,8 @@ 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);

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 3ac978989dab467f04d315d185beddcfa0d50c02..ffba2076c42e59b2d10245e2867811c0781dcf60 100644 (file)
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -962,11 +962,11 @@ static bool xprt_dynamic_free_slot(struct rpc_xprt *xprt, struct rpc_rqst *req)
        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);
@@ -987,12 +987,29 @@ static void xprt_alloc_slot(struct rpc_task *task)
        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)
 {
@@ -1076,20 +1093,9 @@ 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)

diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
index 06cdbff79e4af433d5a4ea3a2766d6d09a9b5a01..5d9202dc7cb127f5158a2a6e275fa0656c18f0a6 100644 (file)
--- a/net/sunrpc/xprtrdma/transport.c
+++ b/net/sunrpc/xprtrdma/transport.c
@@ -713,6 +713,7 @@ static void xprt_rdma_print_stats(struct rpc_xprt *xprt, struct seq_file *seq)
 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 */

diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 1a6edc7e8c862b356e5b62f18076fdc4876f05d9..c5391af32d6a0b81c2fc6c886da5fcd6178628f7 100644 (file)
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -2422,6 +2422,7 @@ static void bc_destroy(struct rpc_xprt *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,
@@ -2438,6 +2439,7 @@ 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,
@@ -2455,6 +2457,7 @@ 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,