Fix segfault in LG_lane_new

STACK_END macro was used to check stack size of child Lua state _after_
its thread was launched. That could lead to the check failing as the child
thread started manipulating the stack. The macro then called lua_error
on the child state from the parent thread, causing a segfault as Lua C API
is not thread-safe.

The fix is to place STACK_END statements before THREAD_CREATE statement.

1 files changed, 3 insertions, 3 deletions

diff --git a/src/lanes.c b/src/lanes.c
index 9b95469..8852687 100644
--- a/src/lanes.c
+++ b/src/lanes.c
@@ -2419,13 +2419,13 @@ LUAG_FUNC( lane_new)
                 lua_sethook( L2, cancel_hook, LUA_MASKCOUNT, cancelstep_idx);
         }
 
+        STACK_END( L, 1);
+        STACK_END( L2, 1 + nargs);
+
         DEBUGSPEW_CODE( fprintf( stderr, INDENT_BEGIN "lane_new: launching thread\n" INDENT_END));
         THREAD_CREATE( &s->thread, lane_main, s, priority);
 
         DEBUGSPEW_CODE( -- U->debugspew_indent_depth);
-
-        STACK_END( L, 1);
-        STACK_END( L2, 1 + nargs);
         return 1;
 }