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.

4 files changed, 23 insertions, 8 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 3e901d84db9..705b9c771df 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,13 @@
+2013-09-01  Eli Zaretskii  <eliz@gnu.org>
+
+        * 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.
+
+        * thread.c (post_acquire_global_lock): Update current_thread
+        before calling unbind_for_thread_switch.  Pass the previous thread
+        to unbind_for_thread_switch.
+
 2013-08-31  Eli Zaretskii  <eliz@gnu.org>
 
         * systhread.c (sys_cond_init): Set the 'initialized' member to
diff --git a/src/eval.c b/src/eval.c
index 68a3691ad9b..b8a61590387 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -3484,11 +3484,11 @@ unbind_to (ptrdiff_t count, Lisp_Object value)
 }
 
 void
-unbind_for_thread_switch (void)
+unbind_for_thread_switch (struct thread_state *thr)
 {
   union specbinding *bind;
 
-  for (bind = specpdl_ptr; bind != specpdl; --bind)
+  for (bind = thr->m_specpdl_ptr; bind != thr->m_specpdl; --bind)
     {
       if (bind->kind >= SPECPDL_LET)
         {
diff --git a/src/lisp.h b/src/lisp.h
index 51c09e0abb3..03628e13ac2 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3828,7 +3828,7 @@ extern void set_unwind_protect (ptrdiff_t, void (*) (Lisp_Object), Lisp_Object);
 extern void set_unwind_protect_ptr (ptrdiff_t, void (*) (void *), void *);
 extern Lisp_Object unbind_to (ptrdiff_t, Lisp_Object);
 extern void rebind_for_thread_switch (void);
-extern void unbind_for_thread_switch (void);
+extern void unbind_for_thread_switch (struct thread_state *);
 extern _Noreturn void error (const char *, ...) ATTRIBUTE_FORMAT_PRINTF (1, 2);
 extern _Noreturn void verror (const char *, va_list)
   ATTRIBUTE_FORMAT_PRINTF (1, 0);
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 ();
     }