[PATCH dlm/next 11/12] fs: dlm: handle sequence numbers as atomic

[Alexander Aring <aahringo@xxxxxxxxxx>]

Currently seq_next is only be read on the receive side which processed
in an ordered way. The seq_send is being protected by locks. To being
able to read the seq_next value on send side as well we convert it to an
atomic_t value. The atomic_cmpxchg() is probably not necessary, however
the atomic_inc() depends on a if coniditional and this should be handled
in an atomic context.

Signed-off-by: Alexander Aring <aahringo@xxxxxxxxxx>
---
 fs/dlm/midcomms.c | 40 +++++++++++++++++++++++++---------------
 1 file changed, 25 insertions(+), 15 deletions(-)

diff --git a/fs/dlm/midcomms.c b/fs/dlm/midcomms.c
index 9c66cb853d17..70286737eb0a 100644
--- a/fs/dlm/midcomms.c
+++ b/fs/dlm/midcomms.c
@@ -152,8 +152,8 @@
 struct midcomms_node {
 	int nodeid;
 	uint32_t version;
-	uint32_t seq_send;
-	uint32_t seq_next;
+	atomic_t seq_send;
+	atomic_t seq_next;
 	/* These queues are unbound because we cannot drop any message in dlm.
 	 * We could send a fence signal for a specific node to the cluster
 	 * manager if queues hits some maximum value, however this handling
@@ -317,8 +317,8 @@ static void midcomms_node_reset(struct midcomms_node *node)
 {
 	pr_debug("reset node %d\n", node->nodeid);
 
-	node->seq_next = DLM_SEQ_INIT;
-	node->seq_send = DLM_SEQ_INIT;
+	atomic_set(&node->seq_next, DLM_SEQ_INIT);
+	atomic_set(&node->seq_send, DLM_SEQ_INIT);
 	node->version = DLM_VERSION_NOT_SET;
 	node->flags = 0;
 
@@ -492,9 +492,19 @@ static void dlm_midcomms_receive_buffer(union dlm_packet *p,
 					struct midcomms_node *node,
 					uint32_t seq)
 {
-	if (seq == node->seq_next) {
-		node->seq_next++;
+	bool is_expected_seq;
+	uint32_t oval, nval;
 
+	do {
+		oval = atomic_read(&node->seq_next);
+		is_expected_seq = (oval == seq);
+		if (!is_expected_seq)
+			break;
+
+		nval = oval + 1;
+	} while (atomic_cmpxchg(&node->seq_next, oval, nval) != oval);
+
+	if (is_expected_seq) {
 		switch (p->header.h_cmd) {
 		case DLM_FIN:
 			spin_lock(&node->state_lock);
@@ -503,7 +513,7 @@ static void dlm_midcomms_receive_buffer(union dlm_packet *p,
 
 			switch (node->state) {
 			case DLM_ESTABLISHED:
-				dlm_send_ack(node->nodeid, node->seq_next);
+				dlm_send_ack(node->nodeid, nval);
 
 				/* passive shutdown DLM_LAST_ACK case 1
 				 * additional we check if the node is used by
@@ -522,14 +532,14 @@ static void dlm_midcomms_receive_buffer(union dlm_packet *p,
 				}
 				break;
 			case DLM_FIN_WAIT1:
-				dlm_send_ack(node->nodeid, node->seq_next);
+				dlm_send_ack(node->nodeid, nval);
 				node->state = DLM_CLOSING;
 				set_bit(DLM_NODE_FLAG_STOP_RX, &node->flags);
 				pr_debug("switch node %d to state %s\n",
 					 node->nodeid, dlm_state_str(node->state));
 				break;
 			case DLM_FIN_WAIT2:
-				dlm_send_ack(node->nodeid, node->seq_next);
+				dlm_send_ack(node->nodeid, nval);
 				midcomms_node_reset(node);
 				pr_debug("switch node %d to state %s\n",
 					 node->nodeid, dlm_state_str(node->state));
@@ -557,11 +567,11 @@ static void dlm_midcomms_receive_buffer(union dlm_packet *p,
 		/* retry to ack message which we already have by sending back
 		 * current node->seq_next number as ack.
 		 */
-		if (seq < node->seq_next)
-			dlm_send_ack(node->nodeid, node->seq_next);
+		if (seq < oval)
+			dlm_send_ack(node->nodeid, oval);
 
 		log_print_ratelimited("ignore dlm msg because seq mismatch, seq: %u, expected: %u, nodeid: %d",
-				      seq, node->seq_next, node->nodeid);
+				      seq, oval, node->nodeid);
 	}
 }
 
@@ -992,7 +1002,7 @@ void dlm_midcomms_receive_done(int nodeid)
 	switch (node->state) {
 	case DLM_ESTABLISHED:
 		spin_unlock(&node->state_lock);
-		dlm_send_ack(node->nodeid, node->seq_next);
+		dlm_send_ack(node->nodeid, atomic_read(&node->seq_next));
 		break;
 	default:
 		spin_unlock(&node->state_lock);
@@ -1058,7 +1068,7 @@ static void midcomms_new_msg_cb(void *data)
 	list_add_tail_rcu(&mh->list, &mh->node->send_queue);
 	spin_unlock_bh(&mh->node->send_queue_lock);
 
-	mh->seq = mh->node->seq_send++;
+	mh->seq = atomic_fetch_inc(&mh->node->seq_send);
 }
 
 static struct dlm_msg *dlm_midcomms_get_msg_3_2(struct dlm_mhandle *mh, int nodeid,
@@ -1530,7 +1540,7 @@ static void midcomms_new_rawmsg_cb(void *data)
 		switch (h->h_cmd) {
 		case DLM_OPTS:
 			if (!h->u.h_seq)
-				h->u.h_seq = cpu_to_le32(rd->node->seq_send++);
+				h->u.h_seq = cpu_to_le32(atomic_fetch_inc(&rd->node->seq_send));
 			break;
 		default:
 			break;
-- 
2.31.1