[PATCH v5 16/30] xprtrdma: Simplify locking that protects the rl_allreqs list

[Chuck Lever <chuck.lever@xxxxxxxxxx>]

Clean up: There's little chance of contention between the use of
rb_lock and rb_reqslock, so merge the two. This avoids having to
take both in some (possibly future) cases.

Transport tear-down is already serialized, thus there is no need for
locking at all when destroying rpcrdma_reqs.

Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
 net/sunrpc/xprtrdma/backchannel.c |   20 +++-----------------
 net/sunrpc/xprtrdma/verbs.c       |   31 +++++++++++++++++--------------
 net/sunrpc/xprtrdma/xprt_rdma.h   |    7 +++----
 3 files changed, 23 insertions(+), 35 deletions(-)

diff --git a/net/sunrpc/xprtrdma/backchannel.c b/net/sunrpc/xprtrdma/backchannel.c
index e2704db..aae2eb1 100644
--- a/net/sunrpc/xprtrdma/backchannel.c
+++ b/net/sunrpc/xprtrdma/backchannel.c
@@ -19,29 +19,16 @@
 
 #undef RPCRDMA_BACKCHANNEL_DEBUG
 
-static void rpcrdma_bc_free_rqst(struct rpcrdma_xprt *r_xprt,
-				 struct rpc_rqst *rqst)
-{
-	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
-	struct rpcrdma_req *req = rpcr_to_rdmar(rqst);
-
-	spin_lock(&buf->rb_reqslock);
-	list_del(&req->rl_all);
-	spin_unlock(&buf->rb_reqslock);
-
-	rpcrdma_destroy_req(req);
-}
-
 static int rpcrdma_bc_setup_reqs(struct rpcrdma_xprt *r_xprt,
 				 unsigned int count)
 {
 	struct rpc_xprt *xprt = &r_xprt->rx_xprt;
+	struct rpcrdma_req *req;
 	struct rpc_rqst *rqst;
 	unsigned int i;
 
 	for (i = 0; i < (count << 1); i++) {
 		struct rpcrdma_regbuf *rb;
-		struct rpcrdma_req *req;
 		size_t size;
 
 		req = rpcrdma_create_req(r_xprt);
@@ -67,7 +54,7 @@ static int rpcrdma_bc_setup_reqs(struct rpcrdma_xprt *r_xprt,
 	return 0;
 
 out_fail:
-	rpcrdma_bc_free_rqst(r_xprt, rqst);
+	rpcrdma_req_destroy(req);
 	return -ENOMEM;
 }
 
@@ -225,7 +212,6 @@ int xprt_rdma_bc_send_reply(struct rpc_rqst *rqst)
  */
 void xprt_rdma_bc_destroy(struct rpc_xprt *xprt, unsigned int reqs)
 {
-	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
 	struct rpc_rqst *rqst, *tmp;
 
 	spin_lock(&xprt->bc_pa_lock);
@@ -233,7 +219,7 @@ void xprt_rdma_bc_destroy(struct rpc_xprt *xprt, unsigned int reqs)
 		list_del(&rqst->rq_bc_pa_list);
 		spin_unlock(&xprt->bc_pa_lock);
 
-		rpcrdma_bc_free_rqst(r_xprt, rqst);
+		rpcrdma_req_destroy(rpcr_to_rdmar(rqst));
 
 		spin_lock(&xprt->bc_pa_lock);
 	}
diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index 0cce7b2..51e09ae1 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -1043,9 +1043,9 @@ struct rpcrdma_req *
 	req->rl_buffer = buffer;
 	INIT_LIST_HEAD(&req->rl_registered);
 
-	spin_lock(&buffer->rb_reqslock);
+	spin_lock(&buffer->rb_lock);
 	list_add(&req->rl_all, &buffer->rb_allreqs);
-	spin_unlock(&buffer->rb_reqslock);
+	spin_unlock(&buffer->rb_lock);
 	return req;
 }
 
@@ -1113,7 +1113,6 @@ struct rpcrdma_req *
 
 	INIT_LIST_HEAD(&buf->rb_send_bufs);
 	INIT_LIST_HEAD(&buf->rb_allreqs);
-	spin_lock_init(&buf->rb_reqslock);
 	for (i = 0; i < buf->rb_max_requests; i++) {
 		struct rpcrdma_req *req;
 
@@ -1154,9 +1153,18 @@ struct rpcrdma_req *
 	kfree(rep);
 }
 
+/**
+ * rpcrdma_req_destroy - Destroy an rpcrdma_req object
+ * @req: unused object to be destroyed
+ *
+ * This function assumes that the caller prevents concurrent device
+ * unload and transport tear-down.
+ */
 void
-rpcrdma_destroy_req(struct rpcrdma_req *req)
+rpcrdma_req_destroy(struct rpcrdma_req *req)
 {
+	list_del(&req->rl_all);
+
 	rpcrdma_free_regbuf(req->rl_recvbuf);
 	rpcrdma_free_regbuf(req->rl_sendbuf);
 	rpcrdma_free_regbuf(req->rl_rdmabuf);
@@ -1214,19 +1222,14 @@ struct rpcrdma_req *
 		rpcrdma_destroy_rep(rep);
 	}
 
-	spin_lock(&buf->rb_reqslock);
-	while (!list_empty(&buf->rb_allreqs)) {
+	while (!list_empty(&buf->rb_send_bufs)) {
 		struct rpcrdma_req *req;
 
-		req = list_first_entry(&buf->rb_allreqs,
-				       struct rpcrdma_req, rl_all);
-		list_del(&req->rl_all);
-
-		spin_unlock(&buf->rb_reqslock);
-		rpcrdma_destroy_req(req);
-		spin_lock(&buf->rb_reqslock);
+		req = list_first_entry(&buf->rb_send_bufs,
+				       struct rpcrdma_req, rl_list);
+		list_del(&req->rl_list);
+		rpcrdma_req_destroy(req);
 	}
-	spin_unlock(&buf->rb_reqslock);
 
 	rpcrdma_mrs_destroy(buf);
 }
diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
index ff4eab1..a1cdc85 100644
--- a/net/sunrpc/xprtrdma/xprt_rdma.h
+++ b/net/sunrpc/xprtrdma/xprt_rdma.h
@@ -392,14 +392,13 @@ struct rpcrdma_buffer {
 	spinlock_t		rb_lock;	/* protect buf lists */
 	struct list_head	rb_send_bufs;
 	struct list_head	rb_recv_bufs;
+	struct list_head	rb_allreqs;
+
 	unsigned long		rb_flags;
 	u32			rb_max_requests;
 	u32			rb_credits;	/* most recent credit grant */
 
 	u32			rb_bc_srv_max_requests;
-	spinlock_t		rb_reqslock;	/* protect rb_allreqs */
-	struct list_head	rb_allreqs;
-
 	u32			rb_bc_max_requests;
 
 	struct workqueue_struct *rb_completion_wq;
@@ -522,7 +521,7 @@ int rpcrdma_ep_post(struct rpcrdma_ia *, struct rpcrdma_ep *,
  * Buffer calls - xprtrdma/verbs.c
  */
 struct rpcrdma_req *rpcrdma_create_req(struct rpcrdma_xprt *);
-void rpcrdma_destroy_req(struct rpcrdma_req *);
+void rpcrdma_req_destroy(struct rpcrdma_req *req);
 int rpcrdma_buffer_create(struct rpcrdma_xprt *);
 void rpcrdma_buffer_destroy(struct rpcrdma_buffer *);
 struct rpcrdma_sendctx *rpcrdma_sendctx_get_locked(struct rpcrdma_buffer *buf);