Fix crashes when unbind_for_thread_switch signals an error.

 src/eval.c (unbind_for_thread_switch): Accept a 'struct
 thread_state *' argument and use specpdl_ptr and specpdl of that
 thread.  Fixes crashes if find_symbol_value signals an error.
 src/thread.c (post_acquire_global_lock): Update current_thread
 before calling unbind_for_thread_switch.  Pass the previous thread
 to unbind_for_thread_switch.

1 files changed, 10 insertions, 5 deletions

diff --git a/src/thread.c b/src/thread.c
index 39a21518ec6..f060a002a3a 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -55,15 +55,20 @@ static void
 post_acquire_global_lock (struct thread_state *self)
 {
   Lisp_Object buffer;
+  struct thread_state *prev_thread = current_thread;
 
-  if (self != current_thread)
+  /* Do this early on, so that code below could signal errors (e.g.,
+     unbind_for_thread_switch might) correctly, because we are already
+     running in the context of the thread pointed by SELF.  */
+  current_thread = self;
+
+  if (prev_thread != current_thread)
     {
-      /* CURRENT_THREAD is NULL if the previously current thread
+      /* PREV_THREAD is NULL if the previously current thread
          exited.  In this case, there is no reason to unbind, and
          trying will crash.  */
-      if (current_thread != NULL)
-        unbind_for_thread_switch ();
-      current_thread = self;
+      if (prev_thread != NULL)
+        unbind_for_thread_switch (prev_thread);
       rebind_for_thread_switch ();
     }