[Cluster-devel] [PATCH dlm-next 3/4] fs: dlm: change handling of reconnects

[Alexander Aring <aahringo@redhat.com>]

This patch changes the handling of reconnects. At first we only close
the connection related to the communication failure. If we get a new
connection for an already existing connection we close the existing
connection and take the new one.

This patch improves significantly the stability of tcp connections while
running "tcpkill -9 -i $IFACE port 21064" while generating a lot of dlm
messages e.g. on a gfs2 mount and [0]. My test setup shows that a
deadlock is "more" unlikely. Before this patch I wasn't able to get
not a deadlock after 5 seconds. After this patch my observation is
that it's more likely to survive after 5 seconds and more, but still a
deadlock occurs after certain time. My guess is that there are still
"segments" inside the tcp writequeue or retransmit queue which get dropped
when receiving a tcp reset [1]. Hard to reproduce because the right message
need to be inside these queues, which might even be in the 5 first seconds
with this patch.

[0] https://fedorapeople.org/cgit/teigland/public_git/dct-stuff.git/tree/fs/make_panic
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/net/ipv4/tcp_input.c?h=v5.8-rc6#n4122

Signed-off-by: Alexander Aring <aahringo@redhat.com>
---
 fs/dlm/lowcomms.c | 25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
index 19b50d69babef..f5ac40db5e7c1 100644
--- a/fs/dlm/lowcomms.c
+++ b/fs/dlm/lowcomms.c
@@ -711,7 +711,7 @@ static int receive_from_sock(struct connection *con)
 out_close:
 	mutex_unlock(&con->sock_mutex);
 	if (ret != -EAGAIN) {
-		close_connection(con, true, true, false);
+		close_connection(con, false, true, false);
 		/* Reconnect when there is something to send */
 	}
 	/* Don't return success if we really got EOF */
@@ -802,21 +802,16 @@ static int accept_from_sock(struct connection *con)
 			INIT_WORK(&othercon->swork, process_send_sockets);
 			INIT_WORK(&othercon->rwork, process_recv_sockets);
 			set_bit(CF_IS_OTHERCON, &othercon->flags);
+		} else {
+			/* close other sock con if we have something new */
+			close_connection(othercon, false, true, false);
 		}
+
 		mutex_lock_nested(&othercon->sock_mutex, 2);
-		if (!othercon->sock) {
-			newcon->othercon = othercon;
-			add_sock(newsock, othercon);
-			addcon = othercon;
-			mutex_unlock(&othercon->sock_mutex);
-		}
-		else {
-			printk("Extra connection from node %d attempted\n", nodeid);
-			result = -EAGAIN;
-			mutex_unlock(&othercon->sock_mutex);
-			mutex_unlock(&newcon->sock_mutex);
-			goto accept_err;
-		}
+		newcon->othercon = othercon;
+		add_sock(newsock, othercon);
+		addcon = othercon;
+		mutex_unlock(&othercon->sock_mutex);
 	}
 	else {
 		newcon->rx_action = receive_from_sock;
@@ -1413,7 +1408,7 @@ static void send_to_sock(struct connection *con)
 
 send_error:
 	mutex_unlock(&con->sock_mutex);
-	close_connection(con, true, false, true);
+	close_connection(con, false, false, true);
 	/* Requeue the send work. When the work daemon runs again, it will try
 	   a new connection, then call this function again. */
 	queue_work(send_workqueue, &con->swork);
-- 
2.26.2