xprtrdma: Protect ia->ri_id when unmapping/invalidating MRs

Ensure ia->ri_id remains valid while invoking dma_unmap_page() or
posting LOCAL_INV during a transport reconnect. Otherwise,
ia->ri_id->device or ia->ri_id->qp is NULL, which triggers a panic.

BugLink: https://bugzilla.linux-nfs.org/show_bug.cgi?id=259
Fixes: ec62f40 'xprtrdma: Ensure ia->ri_id->qp is not NULL when reconnecting'
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Tested-by: Shirley Ma <shirley.ma@oracle.com>
Tested-by: Devesh Sharma <devesh.sharma@emulex.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index f337bda..aa08de89 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -613,6 +613,7 @@
 	/* Else will do memory reg/dereg for each chunk */
 	ia->ri_memreg_strategy = memreg;
 
+	rwlock_init(&ia->ri_qplock);
 	return 0;
 out2:
 	rdma_destroy_id(ia->ri_id);
@@ -859,7 +860,7 @@
 int
 rpcrdma_ep_connect(struct rpcrdma_ep *ep, struct rpcrdma_ia *ia)
 {
-	struct rdma_cm_id *id;
+	struct rdma_cm_id *id, *old;
 	int rc = 0;
 	int retry_count = 0;
 
@@ -905,9 +906,14 @@
 			rc = -ENETUNREACH;
 			goto out;
 		}
-		rdma_destroy_qp(ia->ri_id);
-		rdma_destroy_id(ia->ri_id);
+
+		write_lock(&ia->ri_qplock);
+		old = ia->ri_id;
 		ia->ri_id = id;
+		write_unlock(&ia->ri_qplock);
+
+		rdma_destroy_qp(old);
+		rdma_destroy_id(old);
 	} else {
 		dprintk("RPC:       %s: connecting...\n", __func__);
 		rc = rdma_create_qp(ia->ri_id, ia->ri_pd, &ep->rep_attr);
@@ -1590,9 +1596,6 @@
 	struct ib_send_wr invalidate_wr, *bad_wr;
 	int rc;
 
-	while (seg1->mr_nsegs--)
-		rpcrdma_unmap_one(ia, seg++);
-
 	memset(&invalidate_wr, 0, sizeof invalidate_wr);
 	invalidate_wr.wr_id = (unsigned long)(void *)seg1->mr_chunk.rl_mw;
 	invalidate_wr.opcode = IB_WR_LOCAL_INV;
@@ -1600,7 +1603,11 @@
 	invalidate_wr.ex.invalidate_rkey = seg1->mr_chunk.rl_mw->r.frmr.fr_mr->rkey;
 	DECR_CQCOUNT(&r_xprt->rx_ep);
 
+	read_lock(&ia->ri_qplock);
+	while (seg1->mr_nsegs--)
+		rpcrdma_unmap_one(ia, seg++);
 	rc = ib_post_send(ia->ri_id->qp, &invalidate_wr, &bad_wr);
+	read_unlock(&ia->ri_qplock);
 	if (rc)
 		dprintk("RPC:       %s: failed ib_post_send for invalidate,"
 			" status %i\n", __func__, rc);
@@ -1661,8 +1668,10 @@
 
 	list_add(&seg1->mr_chunk.rl_mw->r.fmr->list, &l);
 	rc = ib_unmap_fmr(&l);
+	read_lock(&ia->ri_qplock);
 	while (seg1->mr_nsegs--)
 		rpcrdma_unmap_one(ia, seg++);
+	read_unlock(&ia->ri_qplock);
 	if (rc)
 		dprintk("RPC:       %s: failed ib_unmap_fmr,"
 			" status %i\n", __func__, rc);
@@ -1718,7 +1727,9 @@
 
 #if RPCRDMA_PERSISTENT_REGISTRATION
 	case RPCRDMA_ALLPHYSICAL:
+		read_lock(&ia->ri_qplock);
 		rpcrdma_unmap_one(ia, seg);
+		read_unlock(&ia->ri_qplock);
 		break;
 #endif