Elf: Fix also _module_index_list

Fix also concurrent use of _module_index_list (for the per-module TLS).
Use a new mutex _module_index_list mutex to protect it. We could
probably have done something with the RCU instead, but just adding a
new mutex is a lot easier.

Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>

core/elf.cc

@@ -1100,6 +1100,7 @@ init_table get_init(Elf64_Ehdr* header)
 
 ulong program::register_dtv(object* obj)
 {
+    SCOPE_LOCK(_module_index_list_mutex);
     auto i = find(_module_index_list, nullptr);
     if (i != _module_index_list.end()) {
         *i = obj;
@@ -1112,6 +1113,7 @@ ulong program::register_dtv(object* obj)
 
 void program::free_dtv(object* obj)
 {
+    SCOPE_LOCK(_module_index_list_mutex);
     auto i = find(_module_index_list, obj);
     assert(i != _module_index_list.end());
     *i = nullptr;
@@ -1119,6 +1121,7 @@ void program::free_dtv(object* obj)
 
 void* program::tls_addr(ulong module)
 {
+    SCOPE_LOCK(_module_index_list_mutex);
     return _module_index_list[module]->tls_addr();
 }
 

include/osv/elf.hh

@@ -475,6 +475,7 @@ private:
     // used to determine object::_module_index, so indexes
     // are stable even when objects are deleted:
     std::vector<object*> _module_index_list;
+    mutex _module_index_list_mutex;
     std::vector<std::string> _search_path;
     osv::rcu_ptr<modules_list> _modules_rcu;
     modules_list modules_get() const;