glusterd: Protect the peer list and peerinfos with RCU.

The peer list and the peerinfo objects are now protected using RCU.
Design patterns described in the Paul McKenney's RCU dissertation [1]
(sections 5 and 6) have been used to convert existing non-RCU protected
code to RCU protected code.

Currently, we are only targetting guaranteeing the existence of the
peerinfo objects, ie., we are only looking to protect deletes, not all
updaters. We chose this, as protecting all updates is a much more
complex task.

The steps used to accomplish this are,

1. Remove all long lived direct references to peerinfo objects (apart
from the peerinfo list). This includes references in glusterd_peerctx_t
(RPC), glusterd_friend_sm_event_t (friend state machine) and others.
This way no one has a reference to deleted peerinfo object.

2. Replace the direct references with indirect references, ie., use
peer uuid and peer hostname as indirect references to the peerinfo
object. Any reader or updater now uses the indirect references to get to
the actual peerinfo object, using glusterd_peerinfo_find. Cases where a
peerinfo cannot be found are handled gracefully.

3. The readers get and use the peerinfo object only within a RCU read
critical section. This prevents the object from being deleted/freed when
in actual use.

4. The deletion of a peerinfo object is done in a ordered manner
(glusterd_peerinfo_destroy). The object is first removed from the
peerinfo list using an atomic list remove, but the list head is not
reset to allow existing list readers to complete correctly. We wait for
readers to complete, before resetting the list head. This removes the
object from the list completely. After this no new readers can get a
reference to the object, and it can be freed.

This change was developed on the git branch at [2]. This commit is a
combination of the following commits on the development branch.
  d7999b9 Protect the glusterd_conf_t->peers_list with RCU.
  0da85c4 Synchronize before INITing peerinfo list head after removing
          from list.
  32ec28a Add missing rcu_read_unlock
  8fed0b8 Correctly exit read critical section once peer is found.
  63db857 Free peerctx only on rpc destruction
  56eff26 Cleanup style issues
  e5f38b0 Indirection for events and friend_sm
  3c84ac4 In __glusterd_probe_cbk goto unlock only if peer already
          exists
  141d855 Address review comments on 9695/1
  aaeefed Protection during peer updates
  6eda33d Revert "Synchronize before INITing peerinfo list head after
          removing from list."
  f69db96 Remove unneeded line
  b43d2ec Address review comments on 9695/4
  7781921 Address review comments on 9695/5
  eb6467b Add some missing semi-colons
  328a47f Remove synchronize_rcu from
          glusterd_friend_sm_transition_state
  186e429 Run part of glusterd_friend_remove in critical section
  55c0a2e Fix gluster (peer status/ pool list) with no peers
  93f8dcf Use call_rcu to free peerinfo
  c36178c Introduce composite struct, gd_rcu_head

[1]: http://www.rdrop.com/~paulmck/RCU/RCUdissertation.2004.07.14e1.pdf
[2]: https://github.com/kshlm/glusterfs/tree/urcu

Change-Id: Ic1480e59c86d41d25a6a3d159aa3e11fbb3cbc7b
BUG: 1191030
Signed-off-by: Kaushal M <kaushal@redhat.com>
Reviewed-on: http://review.gluster.org/9695
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Atin Mukherjee <amukherj@redhat.com>
Reviewed-by: Anand Nekkunti <anekkunt@redhat.com>
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Krishnan Parthasarathi <kparthas@redhat.com>

1 files changed, 124 insertions, 49 deletions

diff --git a/xlators/mgmt/glusterd/src/glusterd-rpc-ops.c b/xlators/mgmt/glusterd/src/glusterd-rpc-ops.c
index 8dd65168bb6..6025a0748a0 100644
--- a/xlators/mgmt/glusterd/src/glusterd-rpc-ops.c
+++ b/xlators/mgmt/glusterd/src/glusterd-rpc-ops.c
@@ -264,9 +264,13 @@ __glusterd_probe_cbk (struct rpc_req *req, struct iovec *iov,
                 goto out;
         }
 
+        rcu_read_lock ();
         peerinfo = glusterd_peerinfo_find (rsp.uuid, rsp.hostname);
         if (peerinfo == NULL) {
-                GF_ASSERT (0);
+                ret = -1;
+                gf_log (this->name, GF_LOG_ERROR, "Could not find peerd %s(%s)",
+                        rsp.hostname, uuid_utoa (rsp.uuid));
+                goto unlock;
         }
 
         /*
@@ -315,7 +319,9 @@ __glusterd_probe_cbk (struct rpc_req *req, struct iovec *iov,
                 ret = glusterd_friend_sm_new_event (GD_FRIEND_EVENT_LOCAL_ACC,
                                                     &event);
                 if (!ret) {
-                        event->peerinfo = peerinfo;
+                        event->peername = gf_strdup (peerinfo->hostname);
+                        uuid_copy (event->peerid, peerinfo->uuid);
+
                         ret = glusterd_friend_sm_inject_event (event);
                 }
                 rsp.op_errno = GF_PROBE_FRIEND;
@@ -324,7 +330,10 @@ reply:
                 ctx = ((call_frame_t *)myframe)->local;
                 ((call_frame_t *)myframe)->local = NULL;
 
-                GF_ASSERT (ctx);
+                if (!ctx) {
+                        ret = -1;
+                        goto unlock;
+                }
 
                 if (ctx->req) {
                         glusterd_xfer_cli_probe_resp (ctx->req, ret,
@@ -336,7 +345,7 @@ reply:
 
                 glusterd_destroy_probe_ctx (ctx);
 
-                goto out;
+                goto unlock;
 
         } else if (strncasecmp (rsp.hostname, peerinfo->hostname, 1024)) {
                 gf_log (THIS->name, GF_LOG_INFO, "Host: %s  with uuid: %s "
@@ -346,7 +355,10 @@ reply:
                 ctx = ((call_frame_t *)myframe)->local;
                 ((call_frame_t *)myframe)->local = NULL;
 
-                GF_ASSERT (ctx);
+                if (!ctx) {
+                        ret = -1;
+                        goto unlock;
+                }
 
                 rsp.op_errno = GF_PROBE_FRIEND;
                 if (ctx->req) {
@@ -360,8 +372,10 @@ reply:
                 glusterd_destroy_probe_ctx (ctx);
                 (void) glusterd_friend_remove (NULL, rsp.hostname);
                 ret = rsp.op_ret;
-                goto out;
+
+                goto unlock;
         }
+
 cont:
         uuid_copy (peerinfo->uuid, rsp.uuid);
 
@@ -371,25 +385,34 @@ cont:
         if (ret) {
                 gf_log ("glusterd", GF_LOG_ERROR,
                          "Unable to get event");
-                goto out;
+                goto unlock;
         }
 
-        event->peerinfo = peerinfo;
+        event->peername = gf_strdup (peerinfo->hostname);
+        uuid_copy (event->peerid, peerinfo->uuid);
+
         event->ctx      = ((call_frame_t *)myframe)->local;
         ((call_frame_t *)myframe)->local = NULL;
         ret = glusterd_friend_sm_inject_event (event);
 
 
-        if (!ret) {
-                glusterd_friend_sm ();
-                glusterd_op_sm ();
-        }
-
         gf_log ("glusterd", GF_LOG_INFO, "Received resp to probe req");
 
+unlock:
+        rcu_read_unlock ();
+
 out:
         free (rsp.hostname);//malloced by xdr
         GLUSTERD_STACK_DESTROY (((call_frame_t *)myframe));
+
+        /* Attempt to start the state machine. Needed as no state machine could
+         * be running at time this RPC reply was recieved
+         */
+        if (!ret) {
+                glusterd_friend_sm ();
+                glusterd_op_sm ();
+        }
+
         return ret;
 }
 
@@ -437,12 +460,14 @@ __glusterd_friend_add_cbk (struct rpc_req * req, struct iovec *iov,
                 "Received %s from uuid: %s, host: %s, port: %d",
                 (op_ret)?"RJT":"ACC", uuid_utoa (rsp.uuid), rsp.hostname, rsp.port);
 
+        rcu_read_lock ();
+
         peerinfo = glusterd_peerinfo_find (rsp.uuid, rsp.hostname);
         if (peerinfo == NULL) {
                 ret = -1;
                 gf_log ("", GF_LOG_ERROR, "received friend add response from"
                         " unknown peer uuid: %s", uuid_utoa (rsp.uuid));
-                goto out;
+                goto unlock;
         }
 
         if (op_ret)
@@ -455,25 +480,26 @@ __glusterd_friend_add_cbk (struct rpc_req * req, struct iovec *iov,
         if (ret) {
                 gf_log ("glusterd", GF_LOG_ERROR,
                          "Unable to get event");
-                goto out;
+                goto unlock;
         }
-        event->peerinfo = peerinfo;
+
         ev_ctx = GF_CALLOC (1, sizeof (*ev_ctx),
                                 gf_gld_mt_friend_update_ctx_t);
         if (!ev_ctx) {
                 ret = -1;
-                goto out;
+                goto unlock;
         }
 
         uuid_copy (ev_ctx->uuid, rsp.uuid);
         ev_ctx->hostname = gf_strdup (rsp.hostname);
 
+        event->peername = gf_strdup (peerinfo->hostname);
+        uuid_copy (event->peerid, peerinfo->uuid);
         event->ctx = ev_ctx;
         ret = glusterd_friend_sm_inject_event (event);
 
-        if (ret)
-                goto out;
-
+unlock:
+        rcu_read_unlock ();
 out:
         ctx = ((call_frame_t *)myframe)->local;
         ((call_frame_t *)myframe)->local = NULL;
@@ -548,12 +574,14 @@ __glusterd_friend_remove_cbk (struct rpc_req * req, struct iovec *iov,
                 (op_ret)?"RJT":"ACC", uuid_utoa (rsp.uuid), rsp.hostname, rsp.port);
 
 inject:
+        rcu_read_lock ();
+
         peerinfo = glusterd_peerinfo_find (rsp.uuid, ctx->hostname);
         if (peerinfo == NULL) {
                 //can happen as part of rpc clnt connection cleanup
                 //when the frame timeout happens after 30 minutes
                 ret = -1;
-                goto respond;
+                goto unlock;
         }
 
         event_type = GD_FRIEND_EVENT_REMOVE_FRIEND;
@@ -563,14 +591,15 @@ inject:
         if (ret) {
                 gf_log ("glusterd", GF_LOG_ERROR,
                          "Unable to get event");
-                goto respond;
+                goto unlock;
         }
-        event->peerinfo = peerinfo;
+        event->peername = gf_strdup (peerinfo->hostname);
+        uuid_copy (event->peerid, peerinfo->uuid);
 
         ret = glusterd_friend_sm_inject_event (event);
 
         if (ret)
-                goto respond;
+                goto unlock;
 
         /*friend_sm would be moved on CLNT_DISCONNECT, consequently
           cleaning up peerinfo. Else, we run the risk of triggering
@@ -578,6 +607,8 @@ inject:
         */
         op_ret = 0;
 
+unlock:
+        rcu_read_unlock ();
 
 respond:
         ret = glusterd_xfer_cli_deprobe_resp (ctx->req, op_ret, op_errno, NULL,
@@ -695,8 +726,11 @@ __glusterd_cluster_lock_cbk (struct rpc_req *req, struct iovec *iov,
                 "Received lock %s from uuid: %s", (op_ret) ? "RJT" : "ACC",
                 uuid_utoa (rsp.uuid));
 
-        peerinfo = glusterd_peerinfo_find (rsp.uuid, NULL);
-        if (peerinfo == NULL) {
+        rcu_read_lock ();
+        ret = (glusterd_peerinfo_find (rsp.uuid, NULL) == NULL);
+        rcu_read_unlock ();
+
+        if (ret) {
                 gf_log (this->name, GF_LOG_CRITICAL,
                         "cluster lock response received from unknown peer: %s."
                         "Ignoring response", uuid_utoa (rsp.uuid));
@@ -751,7 +785,6 @@ glusterd_mgmt_v3_lock_peers_cbk_fn (struct rpc_req *req, struct iovec *iov,
         int                           ret   = -1;
         int32_t                       op_ret = -1;
         glusterd_op_sm_event_type_t   event_type = GD_OP_EVENT_NONE;
-        glusterd_peerinfo_t           *peerinfo = NULL;
         xlator_t                      *this = NULL;
         call_frame_t                  *frame  = NULL;
         uuid_t                        *txn_id = NULL;
@@ -794,8 +827,11 @@ glusterd_mgmt_v3_lock_peers_cbk_fn (struct rpc_req *req, struct iovec *iov,
                 "Received mgmt_v3 lock %s from uuid: %s",
                 (op_ret) ? "RJT" : "ACC", uuid_utoa (rsp.uuid));
 
-        peerinfo = glusterd_peerinfo_find (rsp.uuid, NULL);
-        if (peerinfo == NULL) {
+        rcu_read_lock ();
+        ret = (glusterd_peerinfo_find (rsp.uuid, NULL) == NULL);
+        rcu_read_unlock ();
+
+        if (ret) {
                 gf_log (this->name, GF_LOG_CRITICAL,
                         "mgmt_v3 lock response received "
                         "from unknown peer: %s. Ignoring response",
@@ -841,7 +877,6 @@ glusterd_mgmt_v3_unlock_peers_cbk_fn (struct rpc_req *req, struct iovec *iov,
         int                           ret   = -1;
         int32_t                       op_ret = -1;
         glusterd_op_sm_event_type_t   event_type = GD_OP_EVENT_NONE;
-        glusterd_peerinfo_t           *peerinfo = NULL;
         xlator_t                      *this = NULL;
         call_frame_t                  *frame = NULL;
         uuid_t                        *txn_id = NULL;
@@ -888,8 +923,11 @@ glusterd_mgmt_v3_unlock_peers_cbk_fn (struct rpc_req *req, struct iovec *iov,
                 (op_ret) ? "RJT" : "ACC",
                 uuid_utoa (rsp.uuid));
 
-        peerinfo = glusterd_peerinfo_find (rsp.uuid, NULL);
-        if (peerinfo == NULL) {
+        rcu_read_lock ();
+        ret = (glusterd_peerinfo_find (rsp.uuid, NULL) == NULL);
+        rcu_read_unlock ();
+
+        if (ret) {
                 gf_msg (this->name, GF_LOG_CRITICAL, 0,
                         GD_MSG_CLUSTER_UNLOCK_FAILED,
                         "mgmt_v3 unlock response received "
@@ -980,8 +1018,11 @@ __glusterd_cluster_unlock_cbk (struct rpc_req *req, struct iovec *iov,
                 "Received unlock %s from uuid: %s",
                 (op_ret)?"RJT":"ACC", uuid_utoa (rsp.uuid));
 
-        peerinfo = glusterd_peerinfo_find (rsp.uuid, NULL);
-        if (peerinfo == NULL) {
+        rcu_read_lock ();
+        ret = (glusterd_peerinfo_find (rsp.uuid, NULL) == NULL);
+        rcu_read_unlock ();
+
+        if (ret) {
                 gf_msg (this->name, GF_LOG_CRITICAL, 0,
                         GD_MSG_CLUSTER_UNLOCK_FAILED,
                         "Unlock response received from unknown peer %s",
@@ -1091,6 +1132,7 @@ out:
         gf_log (this->name, GF_LOG_DEBUG, "transaction ID = %s",
                 uuid_utoa (*txn_id));
 
+        rcu_read_lock ();
         peerinfo = glusterd_peerinfo_find (rsp.uuid, NULL);
         if (peerinfo == NULL) {
                 gf_log (this->name, GF_LOG_CRITICAL, "Stage response received "
@@ -1118,6 +1160,8 @@ out:
                 event_type = GD_OP_EVENT_RCVD_ACC;
         }
 
+        rcu_read_unlock ();
+
         switch (rsp.op) {
         case GD_OP_REPLACE_BRICK:
                 glusterd_rb_use_rsp_dict (NULL, dict);
@@ -1227,6 +1271,7 @@ __glusterd_commit_op_cbk (struct rpc_req *req, struct iovec *iov,
         gf_log (this->name, GF_LOG_DEBUG, "transaction ID = %s",
                 uuid_utoa (*txn_id));
 
+        rcu_read_lock ();
         peerinfo = glusterd_peerinfo_find (rsp.uuid, NULL);
         if (peerinfo == NULL) {
                 gf_log (this->name, GF_LOG_CRITICAL, "Commit response for "
@@ -1250,7 +1295,7 @@ __glusterd_commit_op_cbk (struct rpc_req *req, struct iovec *iov,
                 }
                 if (!opinfo.op_errstr) {
                         ret = -1;
-                        goto out;
+                        goto unlock;
                 }
         } else {
                 event_type = GD_OP_EVENT_RCVD_ACC;
@@ -1258,44 +1303,44 @@ __glusterd_commit_op_cbk (struct rpc_req *req, struct iovec *iov,
                 case GD_OP_REPLACE_BRICK:
                         ret = glusterd_rb_use_rsp_dict (NULL, dict);
                         if (ret)
-                                goto out;
+                                goto unlock;
                 break;
 
                 case GD_OP_SYNC_VOLUME:
                         ret = glusterd_sync_use_rsp_dict (NULL, dict);
                         if (ret)
-                                goto out;
+                                goto unlock;
                 break;
 
                 case GD_OP_PROFILE_VOLUME:
                         ret = glusterd_profile_volume_use_rsp_dict (NULL, dict);
                         if (ret)
-                                goto out;
+                                goto unlock;
                 break;
 
                 case GD_OP_GSYNC_SET:
                         ret = glusterd_gsync_use_rsp_dict (NULL, dict, rsp.op_errstr);
                         if (ret)
-                                goto out;
+                                goto unlock;
                 break;
 
                 case GD_OP_STATUS_VOLUME:
                         ret = glusterd_volume_status_copy_to_op_ctx_dict (NULL, dict);
                         if (ret)
-                                goto out;
+                                goto unlock;
                 break;
 
                 case GD_OP_REBALANCE:
                 case GD_OP_DEFRAG_BRICK_VOLUME:
                         ret = glusterd_volume_rebalance_use_rsp_dict (NULL, dict);
                         if (ret)
-                                goto out;
+                                goto unlock;
                 break;
 
                 case GD_OP_HEAL_VOLUME:
                         ret = glusterd_volume_heal_use_rsp_dict (NULL, dict);
                         if (ret)
-                                goto out;
+                                goto unlock;
 
                 break;
 
@@ -1303,6 +1348,8 @@ __glusterd_commit_op_cbk (struct rpc_req *req, struct iovec *iov,
                 break;
                 }
         }
+unlock:
+        rcu_read_unlock ();
 
 out:
         ret = glusterd_op_sm_inject_event (event_type, txn_id, NULL);
@@ -1397,7 +1444,22 @@ glusterd_rpc_friend_add (call_frame_t *frame, xlator_t *this,
 
         GF_ASSERT (priv);
 
-        peerinfo = event->peerinfo;
+        rcu_read_lock ();
+
+        peerinfo = glusterd_peerinfo_find (event->peerid, event->peername);
+        if (!peerinfo) {
+                rcu_read_unlock ();
+                ret = -1;
+                gf_log (this->name, GF_LOG_ERROR, "Could not find peer %s(%s)",
+                        event->peername, uuid_utoa (event->peerid));
+                goto out;
+        }
+
+        uuid_copy (req.uuid, MY_UUID);
+        req.hostname = gf_strdup (peerinfo->hostname);
+        req.port = peerinfo->port;
+
+        rcu_read_unlock ();
 
         ret = glusterd_add_volumes_to_export_dict (&peer_data);
         if (ret) {
@@ -1425,10 +1487,6 @@ glusterd_rpc_friend_add (call_frame_t *frame, xlator_t *this,
                 }
         }
 
-        uuid_copy (req.uuid, MY_UUID);
-        req.hostname = peerinfo->hostname;
-        req.port = peerinfo->port;
-
         ret = dict_allocate_and_serialize (peer_data, &req.vols.vols_val,
                                            &req.vols.vols_len);
         if (ret)
@@ -1442,6 +1500,7 @@ glusterd_rpc_friend_add (call_frame_t *frame, xlator_t *this,
 
 out:
         GF_FREE (req.vols.vols_val);
+        GF_FREE (req.hostname);
 
         if (peer_data)
                 dict_unref (peer_data);
@@ -1470,17 +1529,31 @@ glusterd_rpc_friend_remove (call_frame_t *frame, xlator_t *this,
 
         GF_ASSERT (priv);
 
-        peerinfo = event->peerinfo;
+        rcu_read_lock ();
+
+        peerinfo = glusterd_peerinfo_find (event->peerid, event->peername);
+        if (!peerinfo) {
+                rcu_read_unlock ();
+                ret = -1;
+                gf_log (this->name, GF_LOG_ERROR, "Could not find peer %s(%s)",
+                        event->peername, uuid_utoa (event->peerid));
+                goto out;
+        }
 
         uuid_copy (req.uuid, MY_UUID);
-        req.hostname = peerinfo->hostname;
+        req.hostname = gf_strdup (peerinfo->hostname);
         req.port = peerinfo->port;
+
+        rcu_read_unlock ();
+
         ret = glusterd_submit_request (peerinfo->rpc, &req, frame, peerinfo->peer,
                                        GLUSTERD_FRIEND_REMOVE, NULL,
                                        this, glusterd_friend_remove_cbk,
                                        (xdrproc_t)xdr_gd1_mgmt_friend_req);
 
 out:
+        GF_FREE (req.hostname);
+
         gf_log ("glusterd", GF_LOG_DEBUG, "Returning %d", ret);
         return ret;
 }
@@ -1507,6 +1580,8 @@ glusterd_rpc_friend_update (call_frame_t *frame, xlator_t *this,
         ret = dict_get_ptr (friends, "peerinfo", VOID(&peerinfo));
         if (ret)
                 goto out;
+        /* Don't want to send the pointer over */
+        dict_del (friends, "peerinfo");
 
         ret = dict_allocate_and_serialize (friends, &req.friends.friends_val,
                                            &req.friends.friends_len);