mon/OSDMonitor: disallow pg_num changes until after pool is created

The pg create handling OSD code does not handle races between a mon create
message and a split message.

Signed-off-by: Sage Weil <sage@redhat.com>

src/mon/CreatingPGs.h

@@ -47,6 +47,17 @@ struct creating_pgs_t {
   /// pools that exist in the osdmap for which at least one pg has been created
   std::set<int64_t> created_pools;
 
+  bool is_creating_pool(int64_t poolid) {
+    if (queue.count(poolid)) {
+      return true;
+    }
+    for (auto& i : pgs) {
+      if ((int64_t)i.first.pool() == poolid) {
+	return true;
+      }
+    }
+    return false;
+  }
   bool create_pool(int64_t poolid, uint32_t pg_num,
 		   epoch_t created, utime_t modified) {
     if (created_pools.count(poolid) == 0) {

src/mon/OSDMonitor.cc

@@ -6065,6 +6065,10 @@ int OSDMonitor::prepare_command_pool_set(const cmdmap_t& cmdmap,
          << " (you may adjust 'mon max pool pg num' for higher values)";
       return -ERANGE;
     }
+    if (creating_pgs.is_creating_pool(pool)) {
+      ss << "still creating initial PGs; cannot update pg_num yet";
+      return -EBUSY;
+    }
     int r = check_pg_num(pool, n, p.get_size(), &ss);
     if (r) {
       return r;