changelog/rpc: Fix rpc_clnt_t mem leaks

PROBLEM:
   1. Freeing up rpc_clnt object might lead to crashes. Well,
      it was not a necessity to free rpc-clnt object till now
      because all the existing use cases needs to reconnect
      back on disconnects. Hence timer code was not taking
      ref on rpc-clnt object.

      Glusterd had some use-cases that led to crash due to
      ping-timer and they fixed only those code paths that
      involve ping-timer.

      Now, since changelog has an use-case where rpc-clnt
      need to be freed up, we need to fix timer code to take
      refs

   2. In changelog, because of issue 1, only mydata was being
      freed which is incorrect. And there are races where
      rpc-clnt object would access the freed mydata which
      would lead to crashes.

      Since changelog xlator resides on brick side and is long
      living process, if multiple libgfchangelog consumers
      register to changelog and disconnect/reconnect mulitple
      times, it would result in leak of 'rpc-clnt' object
      for every connect/disconnect.

SOLUTION:
   1. Handle ref/unref of 'rpc_clnt' structure in timer
      functions properly.
   2. In changelog, unref 'rpc_clnt' in RPC_CLNT_DISCONNECT
      after disabling timers and free mydata on RPC_CLNT_DESTROY.

RPC SETUP IN CHANGELOG:
   1. changelog xlator initiates rpc server say 'changelog_rpc_server'
   2. libgfchangelog initiates one rpc server say 'libgfchangelog_rpc_server'
   3. libgfchangelog initiates rpc client and connects to 'changelog_rpc_server'
   4. In return changelog_rpc_server initiates a rpc client and connects back
      to 'libgfchangelog_rpc_server'

REF/UNREF HANDLING IN TIMER FUNCTIONS:
Let's say rpc clnt refcount = 1
   1. Take the ref before reigstering callback to timer queue
           >>>>  rpc_clnt_ref (say ref count becomes = 2)
   2. Register a callback to timer say 'callback1'
   3. If register fails:
           >>>> rpc_clnt_unref (ref count = 1)
   4. On timer expiration, 'callback1' gets called. So unref rpc clnt at the end
      in 'callback1'. This is corresponding to ref taken in step 1
           >>>> rpc_clnt_unref (ref count = 1)
   5. The cycle from step-1 to step-4 continues....until timer cancel event happens
   6. timer cancel of say 'callback1'
           If timer cancel fails:
                 Do nothing, Step-4 would have unrefd
           If timer cancel succeeds:
                 >>>> rpc_clnt_unref (ref count = 1)

Change-Id: I91389bc511b8b1a17824941970ee8d2c29a74a09
BUG: 1316178
Signed-off-by: Kotresh HR <khiremat@redhat.com>
Reviewed-on: http://review.gluster.org/13658
Smoke: Gluster Build System <jenkins@build.gluster.org>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Raghavendra G <rgowdapp@redhat.com>

2 files changed, 16 insertions, 1 deletions

diff --git a/xlators/features/changelog/src/changelog-ev-handle.c b/xlators/features/changelog/src/changelog-ev-handle.c
index 79652a969bd..77637c7beec 100644
--- a/xlators/features/changelog/src/changelog-ev-handle.c
+++ b/xlators/features/changelog/src/changelog-ev-handle.c
@@ -157,6 +157,13 @@ changelog_rpc_notify (struct rpc_clnt *rpc,
                 break;
         case RPC_CLNT_DISCONNECT:
                 rpc_clnt_disable (crpc->rpc);
+
+                /* rpc_clnt_disable doesn't unref the rpc. It just marks
+                 * the rpc as disabled and cancels reconnection timer.
+                 * Hence unref the rpc object to free it.
+                 */
+                rpc_clnt_unref (crpc->rpc);
+
                 selection = &priv->ev_selection;
 
                 LOCK (&crpc->lock);
@@ -170,6 +177,8 @@ changelog_rpc_notify (struct rpc_clnt *rpc,
                 break;
         case RPC_CLNT_MSG:
         case RPC_CLNT_DESTROY:
+                /* Free up mydata */
+                changelog_rpc_clnt_unref (crpc);
                 break;
         }
 
@@ -253,7 +262,9 @@ get_client (changelog_clnt_t *c_clnt, struct list_head **next)
                 if (*next == &c_clnt->active)
                         goto unblock;
                 crpc = list_entry (*next, changelog_rpc_clnt_t, list);
+                /* ref rpc as DISCONNECT might unref the rpc asynchronously */
                 changelog_rpc_clnt_ref (crpc);
+                rpc_clnt_ref (crpc->rpc);
                 *next = (*next)->next;
         }
  unblock:
@@ -267,6 +278,7 @@ put_client (changelog_clnt_t *c_clnt, changelog_rpc_clnt_t *crpc)
 {
         LOCK (&c_clnt->active_lock);
         {
+                rpc_clnt_unref (crpc->rpc);
                 changelog_rpc_clnt_unref (crpc);
         }
         UNLOCK (&c_clnt->active_lock);
diff --git a/xlators/features/changelog/src/changelog-rpc.c b/xlators/features/changelog/src/changelog-rpc.c
index 76addf18545..4bc24203118 100644
--- a/xlators/features/changelog/src/changelog-rpc.c
+++ b/xlators/features/changelog/src/changelog-rpc.c
@@ -199,7 +199,10 @@ changelog_rpc_clnt_init (xlator_t *this,
                 goto error_return;
         INIT_LIST_HEAD (&crpc->list);
 
-        crpc->ref = 0;
+        /* Take a ref, the last unref will be on RPC_CLNT_DESTROY
+         * which comes as a result of last rpc_clnt_unref.
+         */
+        crpc->ref = 1;
         changelog_set_disconnect_flag (crpc, _gf_false);
 
         crpc->filter = rpc_req->filter;