libceph: pick a different monitor when reconnecting

Don't try to reconnect to the same monitor when we fail to establish
a session within a timeout or it's lost.

For that, pick_new_mon() needs to see the old value of cur_mon, so
don't clear it in __close_session() - all calls to __close_session()
but one are followed by __open_session() anyway.  __open_session() is
only called when a new session needs to be established, so the "already
open?" branch, which is now in the way, is simply dropped.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

1 files changed, 57 insertions, 28 deletions

diff --git a/net/ceph/mon_client.c b/net/ceph/mon_client.c
index 89029916315c..accfded53bae 100644
--- a/net/ceph/mon_client.c
+++ b/net/ceph/mon_client.c
@@ -122,45 +122,74 @@ static void __close_session(struct ceph_mon_client *monc)
         ceph_msg_revoke(monc->m_subscribe);
         ceph_msg_revoke_incoming(monc->m_subscribe_ack);
         ceph_con_close(&monc->con);
-        monc->cur_mon = -1;
+
         monc->pending_auth = 0;
         ceph_auth_reset(monc->auth);
 }
 
 /*
- * Open a session with a (new) monitor.
+ * Pick a new monitor at random and set cur_mon.  If we are repicking
+ * (i.e. cur_mon is already set), be sure to pick a different one.
  */
-static int __open_session(struct ceph_mon_client *monc)
+static void pick_new_mon(struct ceph_mon_client *monc)
 {
-        char r;
-        int ret;
+        int old_mon = monc->cur_mon;
 
-        if (monc->cur_mon < 0) {
-                get_random_bytes(&r, 1);
-                monc->cur_mon = r % monc->monmap->num_mon;
-                dout("open_session num=%d r=%d -> mon%d\n",
-                     monc->monmap->num_mon, r, monc->cur_mon);
-                monc->sub_renew_after = jiffies;  /* i.e., expired */
-                monc->sub_renew_sent = 0;
+        BUG_ON(monc->monmap->num_mon < 1);
 
-                dout("open_session mon%d opening\n", monc->cur_mon);
-                ceph_con_open(&monc->con,
-                              CEPH_ENTITY_TYPE_MON, monc->cur_mon,
-                              &monc->monmap->mon_inst[monc->cur_mon].addr);
+        if (monc->monmap->num_mon == 1) {
+                monc->cur_mon = 0;
+        } else {
+                int max = monc->monmap->num_mon;
+                int o = -1;
+                int n;
+
+                if (monc->cur_mon >= 0) {
+                        if (monc->cur_mon < monc->monmap->num_mon)
+                                o = monc->cur_mon;
+                        if (o >= 0)
+                                max--;
+                }
 
-                /* send an initial keepalive to ensure our timestamp is
-                 * valid by the time we are in an OPENED state */
-                ceph_con_keepalive(&monc->con);
+                n = prandom_u32() % max;
+                if (o >= 0 && n >= o)
+                        n++;
 
-                /* initiatiate authentication handshake */
-                ret = ceph_auth_build_hello(monc->auth,
-                                            monc->m_auth->front.iov_base,
-                                            monc->m_auth->front_alloc_len);
-                __send_prepared_auth_request(monc, ret);
-        } else {
-                dout("open_session mon%d already open\n", monc->cur_mon);
+                monc->cur_mon = n;
         }
-        return 0;
+
+        dout("%s mon%d -> mon%d out of %d mons\n", __func__, old_mon,
+             monc->cur_mon, monc->monmap->num_mon);
+}
+
+/*
+ * Open a session with a new monitor.
+ */
+static void __open_session(struct ceph_mon_client *monc)
+{
+        int ret;
+
+        pick_new_mon(monc);
+
+        monc->sub_renew_after = jiffies; /* i.e., expired */
+        monc->sub_renew_sent = 0;
+
+        dout("%s opening mon%d\n", __func__, monc->cur_mon);
+        ceph_con_open(&monc->con, CEPH_ENTITY_TYPE_MON, monc->cur_mon,
+                      &monc->monmap->mon_inst[monc->cur_mon].addr);
+
+        /*
+         * send an initial keepalive to ensure our timestamp is valid
+         * by the time we are in an OPENED state
+         */
+        ceph_con_keepalive(&monc->con);
+
+        /* initiate authentication handshake */
+        ret = ceph_auth_build_hello(monc->auth,
+                                    monc->m_auth->front.iov_base,
+                                    monc->m_auth->front_alloc_len);
+        BUG_ON(ret <= 0);
+        __send_prepared_auth_request(monc, ret);
 }
 
 static bool __sub_expired(struct ceph_mon_client *monc)
@@ -907,7 +936,7 @@ void ceph_monc_stop(struct ceph_mon_client *monc)
 
         mutex_lock(&monc->mutex);
         __close_session(monc);
-
+        monc->cur_mon = -1;
         mutex_unlock(&monc->mutex);
 
         /*