SUNRPC: Ensure that we grab the XPRT_LOCK before calling xprt_alloc_slot

This throttles the allocation of new slots when the socket is busy
reconnecting and/or is out of buffer space.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 42 insertions, 24 deletions

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index fbdbaf2cd58d..ccd583a46ff6 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -191,10 +191,9 @@ EXPORT_SYMBOL_GPL(xprt_load_transport);
  * transport connects from colliding with writes.  No congestion control
  * is provided.
  */
-int xprt_reserve_xprt(struct rpc_task *task)
+int xprt_reserve_xprt(struct rpc_xprt *xprt, struct rpc_task *task)
 {
         struct rpc_rqst *req = task->tk_rqstp;
-        struct rpc_xprt *xprt = req->rq_xprt;
 
         if (test_and_set_bit(XPRT_LOCKED, &xprt->state)) {
                 if (task == xprt->snd_task)
@@ -202,8 +201,10 @@ int xprt_reserve_xprt(struct rpc_task *task)
                 goto out_sleep;
         }
         xprt->snd_task = task;
-        req->rq_bytes_sent = 0;
-        req->rq_ntrans++;
+        if (req != NULL) {
+                req->rq_bytes_sent = 0;
+                req->rq_ntrans++;
+        }
 
         return 1;
 
@@ -212,7 +213,7 @@ out_sleep:
                         task->tk_pid, xprt);
         task->tk_timeout = 0;
         task->tk_status = -EAGAIN;
-        if (req->rq_ntrans)
+        if (req != NULL && req->rq_ntrans)
                 rpc_sleep_on(&xprt->resend, task, NULL);
         else
                 rpc_sleep_on(&xprt->sending, task, NULL);
@@ -239,9 +240,8 @@ static void xprt_clear_locked(struct rpc_xprt *xprt)
  * integrated into the decision of whether a request is allowed to be
  * woken up and given access to the transport.
  */
-int xprt_reserve_xprt_cong(struct rpc_task *task)
+int xprt_reserve_xprt_cong(struct rpc_xprt *xprt, struct rpc_task *task)
 {
-        struct rpc_xprt *xprt = task->tk_xprt;
         struct rpc_rqst *req = task->tk_rqstp;
 
         if (test_and_set_bit(XPRT_LOCKED, &xprt->state)) {
@@ -249,12 +249,14 @@ int xprt_reserve_xprt_cong(struct rpc_task *task)
                         return 1;
                 goto out_sleep;
         }
+        if (req == NULL) {
+                xprt->snd_task = task;
+                return 1;
+        }
         if (__xprt_get_cong(xprt, task)) {
                 xprt->snd_task = task;
-                if (req) {
-                        req->rq_bytes_sent = 0;
-                        req->rq_ntrans++;
-                }
+                req->rq_bytes_sent = 0;
+                req->rq_ntrans++;
                 return 1;
         }
         xprt_clear_locked(xprt);
@@ -262,7 +264,7 @@ out_sleep:
         dprintk("RPC: %5u failed to lock transport %p\n", task->tk_pid, xprt);
         task->tk_timeout = 0;
         task->tk_status = -EAGAIN;
-        if (req && req->rq_ntrans)
+        if (req != NULL && req->rq_ntrans)
                 rpc_sleep_on(&xprt->resend, task, NULL);
         else
                 rpc_sleep_on(&xprt->sending, task, NULL);
@@ -275,7 +277,7 @@ static inline int xprt_lock_write(struct rpc_xprt *xprt, struct rpc_task *task)
         int retval;
 
         spin_lock_bh(&xprt->transport_lock);
-        retval = xprt->ops->reserve_xprt(task);
+        retval = xprt->ops->reserve_xprt(xprt, task);
         spin_unlock_bh(&xprt->transport_lock);
         return retval;
 }
@@ -291,7 +293,7 @@ static void __xprt_lock_write_next(struct rpc_xprt *xprt)
         task = rpc_wake_up_next(&xprt->resend);
         if (!task) {
                 task = rpc_wake_up_next(&xprt->sending);
-                if (!task)
+                if (task == NULL)
                         goto out_unlock;
         }
 
@@ -310,6 +312,7 @@ out_unlock:
 static void __xprt_lock_write_next_cong(struct rpc_xprt *xprt)
 {
         struct rpc_task *task;
+        struct rpc_rqst *req;
 
         if (test_and_set_bit(XPRT_LOCKED, &xprt->state))
                 return;
@@ -318,16 +321,19 @@ static void __xprt_lock_write_next_cong(struct rpc_xprt *xprt)
         task = rpc_wake_up_next(&xprt->resend);
         if (!task) {
                 task = rpc_wake_up_next(&xprt->sending);
-                if (!task)
+                if (task == NULL)
                         goto out_unlock;
         }
+
+        req = task->tk_rqstp;
+        if (req == NULL) {
+                xprt->snd_task = task;
+                return;
+        }
         if (__xprt_get_cong(xprt, task)) {
-                struct rpc_rqst *req = task->tk_rqstp;
                 xprt->snd_task = task;
-                if (req) {
-                        req->rq_bytes_sent = 0;
-                        req->rq_ntrans++;
-                }
+                req->rq_bytes_sent = 0;
+                req->rq_ntrans++;
                 return;
         }
 out_unlock:
@@ -852,7 +858,7 @@ int xprt_prepare_transmit(struct rpc_task *task)
                 err = req->rq_reply_bytes_recvd;
                 goto out_unlock;
         }
-        if (!xprt->ops->reserve_xprt(task))
+        if (!xprt->ops->reserve_xprt(xprt, task))
                 err = -EAGAIN;
 out_unlock:
         spin_unlock_bh(&xprt->transport_lock);
@@ -933,8 +939,6 @@ static void xprt_alloc_slot(struct rpc_task *task)
         struct rpc_xprt *xprt = task->tk_xprt;
 
         task->tk_status = 0;
-        if (task->tk_rqstp)
-                return;
         if (!list_empty(&xprt->free)) {
                 struct rpc_rqst *req = list_entry(xprt->free.next, struct rpc_rqst, rq_list);
                 list_del_init(&req->rq_list);
@@ -944,7 +948,6 @@ static void xprt_alloc_slot(struct rpc_task *task)
         }
         dprintk("RPC:       waiting for request slot\n");
         task->tk_status = -EAGAIN;
-        task->tk_timeout = 0;
         rpc_sleep_on(&xprt->backlog, task, NULL);
 }
 
@@ -1001,10 +1004,25 @@ void xprt_reserve(struct rpc_task *task)
 {
         struct rpc_xprt *xprt = task->tk_xprt;
 
+        task->tk_status = 0;
+        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;
+
         task->tk_status = -EIO;
         spin_lock(&xprt->reserve_lock);
         xprt_alloc_slot(task);
         spin_unlock(&xprt->reserve_lock);
+        xprt_release_write(xprt, task);
 }
 
 static inline __be32 xprt_alloc_xid(struct rpc_xprt *xprt)