SUNRPC: integrate back-channel processing with svc_recv()

Using svc_recv() for (NFSv4.1) back-channel handling means we have just
one mechanism for waking threads.

Also change kthread_freezable_should_stop() in nfs4_callback_svc() to
kthread_should_stop() as used elsewhere.
kthread_freezable_should_stop() effectively adds a try_to_freeze() call,
and svc_recv() already contains that at an appropriate place.
Signed-off-by: NeilBrown <neilb@suse.de>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfs/callback.c

@@ -78,7 +78,7 @@ nfs4_callback_svc(void *vrqstp)
 
 	set_freezable();
 
-	while (!kthread_freezable_should_stop(NULL))
+	while (!kthread_should_stop())
 		svc_recv(rqstp);
 
 	svc_exit_thread(rqstp);
@@ -86,41 +86,6 @@ nfs4_callback_svc(void *vrqstp)
 }
 
 #if defined(CONFIG_NFS_V4_1)
-/*
- * The callback service for NFSv4.1 callbacks
- */
-static int
-nfs41_callback_svc(void *vrqstp)
-{
-	struct svc_rqst *rqstp = vrqstp;
-	struct svc_serv *serv = rqstp->rq_server;
-	struct rpc_rqst *req;
-	DEFINE_WAIT(wq);
-
-	set_freezable();
-
-	while (!kthread_freezable_should_stop(NULL)) {
-		prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_IDLE);
-		spin_lock_bh(&serv->sv_cb_lock);
-		if (!list_empty(&serv->sv_cb_list)) {
-			req = list_first_entry(&serv->sv_cb_list,
-					struct rpc_rqst, rq_bc_list);
-			list_del(&req->rq_bc_list);
-			spin_unlock_bh(&serv->sv_cb_lock);
-			finish_wait(&serv->sv_cb_waitq, &wq);
-			svc_process_bc(req, rqstp);
-		} else {
-			spin_unlock_bh(&serv->sv_cb_lock);
-			if (!kthread_should_stop())
-				schedule();
-			finish_wait(&serv->sv_cb_waitq, &wq);
-		}
-	}
-
-	svc_exit_thread(rqstp);
-	return 0;
-}
-
 static inline void nfs_callback_bc_serv(u32 minorversion, struct rpc_xprt *xprt,
 		struct svc_serv *serv)
 {
@@ -233,10 +198,7 @@ static struct svc_serv *nfs_callback_create_svc(int minorversion)
 			cb_info->users);
 
 	threadfn = nfs4_callback_svc;
-#if defined(CONFIG_NFS_V4_1)
-	if (minorversion)
-		threadfn = nfs41_callback_svc;
-#else
+#if !defined(CONFIG_NFS_V4_1)
 	if (minorversion)
 		return ERR_PTR(-ENOTSUPP);
 #endif

include/linux/sunrpc/svc.h

@@ -92,8 +92,6 @@ struct svc_serv {
 						 * that arrive over the same
 						 * connection */
 	spinlock_t		sv_cb_lock;	/* protects the svc_cb_list */
-	wait_queue_head_t	sv_cb_waitq;	/* sleep here if there are no
-						 * entries in the svc_cb_list */
 	bool			sv_bc_enabled;	/* service uses backchannel */
 #endif /* CONFIG_SUNRPC_BACKCHANNEL */
 };

net/sunrpc/backchannel_rqst.c

@@ -349,10 +349,8 @@ struct rpc_rqst *xprt_lookup_bc_request(struct rpc_xprt *xprt, __be32 xid)
 }
 
 /*
- * Add callback request to callback list.  The callback
- * service sleeps on the sv_cb_waitq waiting for new
- * requests.  Wake it up after adding enqueing the
- * request.
+ * Add callback request to callback list.  Wake a thread
+ * on the first pool (usually the only pool) to handle it.
  */
 void xprt_complete_bc_request(struct rpc_rqst *req, uint32_t copied)
 {
@@ -371,6 +369,6 @@ void xprt_complete_bc_request(struct rpc_rqst *req, uint32_t copied)
 	xprt_get(xprt);
 	spin_lock(&bc_serv->sv_cb_lock);
 	list_add(&req->rq_bc_list, &bc_serv->sv_cb_list);
-	wake_up(&bc_serv->sv_cb_waitq);
 	spin_unlock(&bc_serv->sv_cb_lock);
+	svc_pool_wake_idle_thread(&bc_serv->sv_pools[0]);
 }

net/sunrpc/svc.c

@@ -440,7 +440,6 @@ __svc_init_bc(struct svc_serv *serv)
 {
 	INIT_LIST_HEAD(&serv->sv_cb_list);
 	spin_lock_init(&serv->sv_cb_lock);
-	init_waitqueue_head(&serv->sv_cb_waitq);
 }
 #else
 static void
@@ -718,6 +717,7 @@ void svc_pool_wake_idle_thread(struct svc_pool *pool)
 
 	set_bit(SP_CONGESTED, &pool->sp_flags);
 }
+EXPORT_SYMBOL_GPL(svc_pool_wake_idle_thread);
 
 static struct svc_pool *
 svc_pool_next(struct svc_serv *serv, struct svc_pool *pool, unsigned int *state)

net/sunrpc/svc_xprt.c

@@ -17,6 +17,7 @@
 #include <linux/sunrpc/svc_xprt.h>
 #include <linux/sunrpc/svcsock.h>
 #include <linux/sunrpc/xprt.h>
+#include <linux/sunrpc/bc_xprt.h>
 #include <linux/module.h>
 #include <linux/netdevice.h>
 #include <trace/events/sunrpc.h>
@@ -719,6 +720,13 @@ rqst_should_sleep(struct svc_rqst *rqstp)
 	if (freezing(current))
 		return false;
 
+#if defined(CONFIG_SUNRPC_BACKCHANNEL)
+	if (svc_is_backchannel(rqstp)) {
+		if (!list_empty(&rqstp->rq_server->sv_cb_list))
+			return false;
+	}
+#endif
+
 	return true;
 }
 
@@ -868,6 +876,25 @@ void svc_recv(struct svc_rqst *rqstp)
 		trace_svc_xprt_dequeue(rqstp);
 		svc_handle_xprt(rqstp, xprt);
 	}
+
+#if defined(CONFIG_SUNRPC_BACKCHANNEL)
+	if (svc_is_backchannel(rqstp)) {
+		struct svc_serv *serv = rqstp->rq_server;
+		struct rpc_rqst *req;
+
+		spin_lock_bh(&serv->sv_cb_lock);
+		req = list_first_entry_or_null(&serv->sv_cb_list,
+					       struct rpc_rqst, rq_bc_list);
+		if (req) {
+			list_del(&req->rq_bc_list);
+			spin_unlock_bh(&serv->sv_cb_lock);
+
+			svc_process_bc(req, rqstp);
+			return;
+		}
+		spin_unlock_bh(&serv->sv_cb_lock);
+	}
+#endif
 }
 EXPORT_SYMBOL_GPL(svc_recv);
 

net/sunrpc/xprtrdma/backchannel.c

@@ -267,7 +267,7 @@ void rpcrdma_bc_receive_call(struct rpcrdma_xprt *r_xprt,
 	list_add(&rqst->rq_bc_list, &bc_serv->sv_cb_list);
 	spin_unlock(&bc_serv->sv_cb_lock);
 
-	wake_up(&bc_serv->sv_cb_waitq);
+	svc_pool_wake_idle_thread(&bc_serv->sv_pools[0]);
 
 	r_xprt->rx_stats.bcall_count++;
 	return;