ndb - fix dd drop table race condition

  add list of pages being unmaped, so we can wait for it to be empty before dropping extents

storage/ndb/src/kernel/blocks/dbtup/Dbtup.hpp

@@ -563,6 +563,8 @@ typedef Ptr<Fragoperrec> FragoperrecPtr;
      */
     Page_request_list::Head m_page_requests[MAX_FREE_LIST];
 
+    DLList<Page>::Head m_unmap_pages;
+
     /**
      * Current extent
      */

storage/ndb/src/kernel/blocks/dbtup/DbtupDiskAlloc.cpp

@@ -956,7 +956,9 @@ Dbtup::disk_page_unmap_callback(Uint32 when,
 
     ArrayPool<Page> *pool= (ArrayPool<Page>*)&m_global_page_pool;
     LocalDLList<Page> list(*pool, alloc.m_dirty_pages[idx]);
+    LocalDLList<Page> list2(*pool, alloc.m_unmap_pages);
     list.remove(pagePtr);
+    list2.add(pagePtr);
 
     if (dirty_count == 0)
     {
@@ -999,6 +1001,10 @@ Dbtup::disk_page_unmap_callback(Uint32 when,
 	     << " cnt: " << dirty_count << " " << (idx & ~0x8000) << endl;
     }
 
+    ArrayPool<Page> *pool= (ArrayPool<Page>*)&m_global_page_pool;
+    LocalDLList<Page> list(*pool, alloc.m_unmap_pages);
+    list.remove(pagePtr);
+
     Tablespace_client tsman(0, c_tsman,
 			    fragPtr.p->fragTableId,
 			    fragPtr.p->fragmentId,

storage/ndb/src/kernel/blocks/dbtup/DbtupMeta.cpp

@@ -1005,7 +1005,20 @@ Dbtup::drop_fragment_unmap_pages(Signal *signal,
 {
   if (tabPtr.p->m_no_of_disk_attributes)
   {
+    jam();
     Disk_alloc_info& alloc_info= fragPtr.p->m_disk_alloc_info;
+
+    if (!alloc_info.m_unmap_pages.isEmpty())
+    {
+      jam();
+      ndbout_c("waiting for unmape pages");
+      signal->theData[0] = ZUNMAP_PAGES;
+      signal->theData[1] = tabPtr.i;
+      signal->theData[2] = fragPtr.i;
+      signal->theData[3] = pos;
+      sendSignal(cownref, GSN_CONTINUEB, signal, 4, JBB);  
+      return;
+    }
     while(alloc_info.m_dirty_pages[pos].isEmpty() && pos < MAX_FREE_LIST)
       pos++;