svcrdma: Use standard Linux lists for context cache

Replace the one-off linked list implementation used to implement the
context cache with the standard Linux list_head lists. Add a context
counter to catch resource leaks. A WARN_ON will be added later to
ensure that we've freed all contexts.
Signed-off-by: Tom Tucker <tom@opengridcomputing.com>

include/linux/sunrpc/svc_rdma.h

@@ -72,7 +72,7 @@ extern atomic_t rdma_stat_sq_prod;
  */
 struct svc_rdma_op_ctxt {
 	struct svc_rdma_op_ctxt *read_hdr;
-	struct svc_rdma_op_ctxt *next;
+	struct list_head free_list;
 	struct xdr_buf arg;
 	struct list_head dto_q;
 	enum ib_wr_opcode wr_op;
@@ -104,7 +104,8 @@ struct svcxprt_rdma {
 
 	struct ib_pd         *sc_pd;
 
-	struct svc_rdma_op_ctxt  *sc_ctxt_head;
+	atomic_t	     sc_ctxt_used;
+	struct list_head     sc_ctxt_free;
 	int		     sc_ctxt_cnt;
 	int		     sc_ctxt_bump;
 	int		     sc_ctxt_max;

net/sunrpc/xprtrdma/svc_rdma_transport.c

@@ -103,8 +103,8 @@ static int rdma_bump_context_cache(struct svcxprt_rdma *xprt)
 		spin_lock_bh(&xprt->sc_ctxt_lock);
 		if (ctxt) {
 			at_least_one = 1;
-			ctxt->next = xprt->sc_ctxt_head;
-			xprt->sc_ctxt_head = ctxt;
+			INIT_LIST_HEAD(&ctxt->free_list);
+			list_add(&ctxt->free_list, &xprt->sc_ctxt_free);
 		} else {
 			/* kmalloc failed...give up for now */
 			xprt->sc_ctxt_cnt--;
@@ -123,7 +123,7 @@ struct svc_rdma_op_ctxt *svc_rdma_get_context(struct svcxprt_rdma *xprt)
 
 	while (1) {
 		spin_lock_bh(&xprt->sc_ctxt_lock);
-		if (unlikely(xprt->sc_ctxt_head == NULL)) {
+		if (unlikely(list_empty(&xprt->sc_ctxt_free))) {
 			/* Try to bump my cache. */
 			spin_unlock_bh(&xprt->sc_ctxt_lock);
 
@@ -136,12 +136,15 @@ struct svc_rdma_op_ctxt *svc_rdma_get_context(struct svcxprt_rdma *xprt)
 			schedule_timeout_uninterruptible(msecs_to_jiffies(500));
 			continue;
 		}
-		ctxt = xprt->sc_ctxt_head;
-		xprt->sc_ctxt_head = ctxt->next;
+		ctxt = list_entry(xprt->sc_ctxt_free.next,
+				  struct svc_rdma_op_ctxt,
+				  free_list);
+		list_del_init(&ctxt->free_list);
 		spin_unlock_bh(&xprt->sc_ctxt_lock);
 		ctxt->xprt = xprt;
 		INIT_LIST_HEAD(&ctxt->dto_q);
 		ctxt->count = 0;
+		atomic_inc(&xprt->sc_ctxt_used);
 		break;
 	}
 	return ctxt;
@@ -163,10 +166,11 @@ void svc_rdma_put_context(struct svc_rdma_op_ctxt *ctxt, int free_pages)
 				 ctxt->sge[i].addr,
 				 ctxt->sge[i].length,
 				 ctxt->direction);
+
 	spin_lock_bh(&xprt->sc_ctxt_lock);
-	ctxt->next = xprt->sc_ctxt_head;
-	xprt->sc_ctxt_head = ctxt;
+	list_add(&ctxt->free_list, &xprt->sc_ctxt_free);
 	spin_unlock_bh(&xprt->sc_ctxt_lock);
+	atomic_dec(&xprt->sc_ctxt_used);
 }
 
 /* ib_cq event handler */
@@ -412,28 +416,29 @@ static void create_context_cache(struct svcxprt_rdma *xprt,
 	xprt->sc_ctxt_max = ctxt_max;
 	xprt->sc_ctxt_bump = ctxt_bump;
 	xprt->sc_ctxt_cnt = 0;
-	xprt->sc_ctxt_head = NULL;
+	atomic_set(&xprt->sc_ctxt_used, 0);
+
+	INIT_LIST_HEAD(&xprt->sc_ctxt_free);
 	for (i = 0; i < ctxt_count; i++) {
 		ctxt = kmalloc(sizeof(*ctxt), GFP_KERNEL);
 		if (ctxt) {
-			ctxt->next = xprt->sc_ctxt_head;
-			xprt->sc_ctxt_head = ctxt;
+			INIT_LIST_HEAD(&ctxt->free_list);
+			list_add(&ctxt->free_list, &xprt->sc_ctxt_free);
 			xprt->sc_ctxt_cnt++;
 		}
 	}
 }
 
-static void destroy_context_cache(struct svc_rdma_op_ctxt *ctxt)
+static void destroy_context_cache(struct svcxprt_rdma *xprt)
 {
-	struct svc_rdma_op_ctxt *next;
-	if (!ctxt)
-		return;
-
-	do {
-		next = ctxt->next;
+	while (!list_empty(&xprt->sc_ctxt_free)) {
+		struct svc_rdma_op_ctxt *ctxt;
+		ctxt = list_entry(xprt->sc_ctxt_free.next,
+				  struct svc_rdma_op_ctxt,
+				  free_list);
+		list_del_init(&ctxt->free_list);
 		kfree(ctxt);
-		ctxt = next;
-	} while (next);
+	}
 }
 
 static struct svcxprt_rdma *rdma_create_xprt(struct svc_serv *serv,
@@ -470,7 +475,7 @@ static struct svcxprt_rdma *rdma_create_xprt(struct svc_serv *serv,
 				     reqs +
 				     cma_xprt->sc_sq_depth +
 				     RPCRDMA_MAX_THREADS + 1); /* max */
-		if (!cma_xprt->sc_ctxt_head) {
+		if (list_empty(&cma_xprt->sc_ctxt_free)) {
 			kfree(cma_xprt);
 			return NULL;
 		}
@@ -976,7 +981,7 @@ static void svc_rdma_free(struct svc_xprt *xprt)
 	if (rdma->sc_pd && !IS_ERR(rdma->sc_pd))
 		ib_dealloc_pd(rdma->sc_pd);
 
-	destroy_context_cache(rdma->sc_ctxt_head);
+	destroy_context_cache(rdma);
 	kfree(rdma);
 }