Postpone cb() to set_immediate() to prevent stack overflows in kv_db

src/client/cluster_client.h

@@ -86,8 +86,8 @@ class cluster_client_t
 #ifdef __MOCK__
 public:
 #endif
-    timerfd_manager_t *tfd;
-    ring_loop_t *ringloop;
+    timerfd_manager_t *tfd = NULL;
+    ring_loop_t *ringloop = NULL;
 
     std::map<pool_id_t, uint64_t> pg_counts;
     std::map<pool_pg_num_t, osd_num_t> pg_primary;

src/kv/kv_db.cpp

@@ -870,7 +870,7 @@ static void get_block(kv_db_t *db, uint64_t offset, int cur_level, int recheck_p
         }
         // Block already in cache, we can proceed
         blk->usage = db->usage_counter;
-        cb(0, BLK_UPDATING);
+        db->cli->msgr.ringloop->set_immediate([=] { cb(0, BLK_UPDATING); });
         return;
     }
     cluster_op_t *op = new cluster_op_t;