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Subject: [PATCH 08/14] SUNRPC: integrate back-channel processing with
 svc_recv() and svc_process()
From:   NeilBrown <neilb@suse.de>
To:     Chuck Lever <chuck.lever@oracle.com>,
        Jeff Layton <jlayton@kernel.org>
Cc:     linux-nfs@vger.kernel.org
Date:   Tue, 18 Jul 2023 16:38:08 +1000
Message-ID: <168966228864.11075.5425376786095915126.stgit@noble.brown>
In-Reply-To: <168966227838.11075.2974227708495338626.stgit@noble.brown>
References: <168966227838.11075.2974227708495338626.stgit@noble.brown>
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Using svc_recv() and svc_process() 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>
---
 fs/nfs/callback.c                 |   46 ++---------------------------------
 include/linux/sunrpc/svc.h        |    6 +++--
 net/sunrpc/backchannel_rqst.c     |    8 ++----
 net/sunrpc/svc.c                  |    2 +-
 net/sunrpc/svc_xprt.c             |   48 ++++++++++++++++++++++++++++++++++++-
 net/sunrpc/xprtrdma/backchannel.c |    2 +-
 6 files changed, 58 insertions(+), 54 deletions(-)

diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index c47834970224..660cec36c45c 100644
--- a/fs/nfs/callback.c
+++ b/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()) {
 		/*
 		 * Listen for a request on the socket
 		 */
@@ -90,45 +90,6 @@ 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;
-	int error;
-	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);
-			dprintk("Invoking bc_svc_process()\n");
-			error = bc_svc_process(serv, req, rqstp);
-			dprintk("bc_svc_process() returned w/ error code= %d\n",
-				error);
-		} 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)
 {
@@ -241,10 +202,7 @@ 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
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 83f31a09c853..15d468d852b5 100644
--- a/include/linux/sunrpc/svc.h
+++ b/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 */
 };
@@ -202,6 +200,10 @@ struct svc_rqst {
 	struct rcu_head		rq_rcu_head;	/* for RCU deferred kfree */
 	struct svc_xprt *	rq_xprt;	/* transport ptr */
 
+#if defined(CONFIG_SUNRPC_BACKCHANNEL)
+	struct rpc_rqst		*rq_cb;		/* callback to be handled */
+#endif
+
 	struct sockaddr_storage	rq_addr;	/* peer address */
 	size_t			rq_addrlen;
 	struct sockaddr_storage	rq_daddr;	/* dest addr of request
diff --git a/net/sunrpc/backchannel_rqst.c b/net/sunrpc/backchannel_rqst.c
index 65a6c6429a53..60b8d310bb27 100644
--- a/net/sunrpc/backchannel_rqst.c
+++ b/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, &bc_serv->sv_pools[0]);
 }
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 170eabc03988..56b4a88776d5 100644
--- a/net/sunrpc/svc.c
+++ b/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
@@ -724,6 +723,7 @@ struct svc_rqst *svc_pool_wake_idle_thread(struct svc_serv *serv,
 	percpu_counter_inc(&pool->sp_threads_starved);
 	return NULL;
 }
+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)
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index c7095ff7d5fd..4fdf1aaa514b 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/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>
@@ -732,6 +733,13 @@ 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;
 }
 
@@ -754,12 +762,31 @@ static void svc_wait_for_work(struct svc_rqst *rqstp)
 
 	set_bit(RQ_BUSY, &rqstp->rq_flags);
 	smp_mb__after_atomic();
+
 	rqstp->rq_xprt = svc_xprt_dequeue(pool);
 	if (rqstp->rq_xprt) {
 		trace_svc_pool_awoken(rqstp);
 		goto out_found;
 	}
 
+#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);
+			rqstp->rq_cb = req;
+		}
+		spin_unlock_bh(&serv->sv_cb_lock);
+		if (rqstp->rq_cb)
+			goto out_found;
+	}
+#endif
+
 	if (!kthread_should_stop())
 		percpu_counter_inc(&pool->sp_threads_no_work);
 	return;
@@ -853,7 +880,7 @@ void svc_recv(struct svc_rqst *rqstp)
 	svc_wait_for_work(rqstp);
 
 	if (rqstp->rq_xprt) {
-		struct svc_serv	*serv = rqstp->rq_server;
+		struct svc_serv *serv = rqstp->rq_server;
 		struct svc_xprt *xprt = rqstp->rq_xprt;
 		int len;
 
@@ -878,6 +905,25 @@ void svc_recv(struct svc_rqst *rqstp)
 			svc_process(rqstp);
 		}
 	}
+#if defined(CONFIG_SUNRPC_BACKCHANNEL)
+	if (svc_is_backchannel(rqstp)) {
+		struct rpc_rqst *cb;
+		int error;
+
+		if (!rqstp->rq_cb)
+			return;
+
+		cb = rqstp->rq_cb;
+		rqstp->rq_cb = NULL;
+
+		dprintk("Invoking bc_svc_process()\n");
+		error = bc_svc_process(rqstp->rq_server, cb, rqstp);
+		dprintk("bc_svc_process() returned w/ error code= %d\n",
+			error);
+		return;
+	}
+#endif
+
 }
 EXPORT_SYMBOL_GPL(svc_recv);
 
diff --git a/net/sunrpc/xprtrdma/backchannel.c b/net/sunrpc/xprtrdma/backchannel.c
index e4d84a13c566..f1e1d4909434 100644
--- a/net/sunrpc/xprtrdma/backchannel.c
+++ b/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, &bc_serv->sv_pools[0]);
 
 	r_xprt->rx_stats.bcall_count++;
 	return;