fs: dlm: change handling of reconnects

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 with many files. 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.

[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>
Signed-off-by: David Teigland <teigland@redhat.com>

diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
index 9e6acbb..289439f 100644 (file)
--- a/fs/dlm/lowcomms.c
+++ b/fs/dlm/lowcomms.c
@@ -713,7 +713,7 @@ out_resched:
 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 */
@@ -804,21 +804,16 @@ 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;
@@ -1415,7 +1410,7 @@ out:
 
 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);