[PATCH] pthread_once hangs when init routine throws an exception [BZ #18435]

This is another attempt at making pthread_once handle throwing exceptions
from the init routine callback.  As the new testcases show, just switching
to the cleanup attribute based cleanup does fix the tst-once5 test, but
breaks the new tst-oncey3 test.  That is because when throwing exceptions,
only the unwind info registered cleanups (i.e. C++ destructors or cleanup
attribute), when cancelling threads and there has been unwind info from the
cancellation point up to whatever needs cleanup both unwind info registered
cleanups and THREAD_SETMEM (self, cleanup, ...) registered cleanups are
invoked, but once we hit some frame with no unwind info, only the
THREAD_SETMEM (self, cleanup, ...) registered cleanups are invoked.
So, to stay fully backwards compatible (allow init routines without
unwind info which encounter cancellation points) and handle exception throwing
we actually need to register the pthread_once cleanups in both unwind info
and in the THREAD_SETMEM (self, cleanup, ...) way.
If an exception is thrown, only the former will happen and we in that case
need to also unregister the THREAD_SETMEM (self, cleanup, ...) registered
handler, because otherwise after catching the exception the user code could
call deeper into the stack some cancellation point, get cancelled and then
a stale cleanup handler would clobber stack and probably crash.
If a thread calling init routine is cancelled and unwind info ends before
the pthread_once frame, it will be cleaned up through self->cleanup as
before.  And if unwind info is present, unwind_stop first calls the
self->cleanup registered handler for the frame, then it will call the
unwind info registered handler but that will already see __do_it == 0
and do nothing.

4 files changed, 64 insertions, 9 deletions

diff --git a/nptl/Makefile b/nptl/Makefile
index 5f85dd7..33766ea 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -386,10 +386,6 @@ xtests += tst-eintr1
 
 test-srcs = tst-oddstacklimit
 
-# Test expected to fail on most targets (except x86_64) due to bug
-# 18435 - pthread_once hangs when init routine throws an exception.
-test-xfail-tst-once5 = yes
-
 gen-as-const-headers = unwindbuf.sym \
 		       pthread-pi-defines.sym
 
diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
index d2fd082..93f3cef 100644
--- a/nptl/pthreadP.h
+++ b/nptl/pthreadP.h
@@ -604,6 +604,67 @@ extern void __pthread_cleanup_pop (struct _pthread_cleanup_buffer *buffer,
 # undef pthread_cleanup_pop
 # define pthread_cleanup_pop(execute)                   \
   __pthread_cleanup_pop (&_buffer, (execute)); }
+
+# if defined __EXCEPTIONS && !defined __cplusplus
+/* Structure to hold the cleanup handler information.  */
+struct __pthread_cleanup_combined_frame
+{
+  void (*__cancel_routine) (void *);
+  void *__cancel_arg;
+  int __do_it;
+  struct _pthread_cleanup_buffer __buffer;
+};
+
+/* Special cleanup macros which register cleanup both using
+   __pthread_cleanup_{push,pop} and using cleanup attribute.  This is needed
+   for pthread_once, so that it supports both throwing exceptions from the
+   pthread_once callback (only cleanup attribute works there) and cancellation
+   of the thread running the callback if the callback or some routines it
+   calls don't have unwind information.  */
+
+static __always_inline void
+__pthread_cleanup_combined_routine (struct __pthread_cleanup_combined_frame
+				    *__frame)
+{
+  if (__frame->__do_it)
+    {
+      __frame->__cancel_routine (__frame->__cancel_arg);
+      __frame->__do_it = 0;
+      __pthread_cleanup_pop (&__frame->__buffer, 0);
+    }
+}
+
+static inline void
+__pthread_cleanup_combined_routine_voidptr (void *__arg)
+{
+  struct __pthread_cleanup_combined_frame *__frame
+    = (struct __pthread_cleanup_combined_frame *) __arg;
+  if (__frame->__do_it)
+    {
+      __frame->__cancel_routine (__frame->__cancel_arg);
+      __frame->__do_it = 0;
+    }
+}
+
+#  define pthread_cleanup_combined_push(routine, arg) \
+  do {									      \
+    void (*__cancel_routine) (void *) = (routine);			      \
+    struct __pthread_cleanup_combined_frame __clframe			      \
+      __attribute__ ((__cleanup__ (__pthread_cleanup_combined_routine)))      \
+      = { .__cancel_routine = __cancel_routine, .__cancel_arg = (arg),	      \
+	  .__do_it = 1 };						      \
+    __pthread_cleanup_push (&__clframe.__buffer,			      \
+			    __pthread_cleanup_combined_routine_voidptr,	      \
+			    &__clframe);
+
+#  define pthread_cleanup_combined_pop(execute) \
+    __pthread_cleanup_pop (&__clframe.__buffer, 0);			      \
+    __clframe.__do_it = 0;						      \
+    if (execute)							      \
+      __cancel_routine (__clframe.__cancel_arg);			      \
+  } while (0)
+
+# endif
 #endif
 
 extern void __pthread_cleanup_push_defer (struct _pthread_cleanup_buffer *buffer,
diff --git a/nptl/pthread_once.c b/nptl/pthread_once.c
index 28d9709..7645da2 100644
--- a/nptl/pthread_once.c
+++ b/nptl/pthread_once.c
@@ -111,11 +111,11 @@ __pthread_once_slow (pthread_once_t *once_control, void (*init_routine) (void))
       /* This thread is the first here.  Do the initialization.
 	 Register a cleanup handler so that in case the thread gets
 	 interrupted the initialization can be restarted.  */
-      pthread_cleanup_push (clear_once_control, once_control);
+      pthread_cleanup_combined_push (clear_once_control, once_control);
 
       init_routine ();
 
-      pthread_cleanup_pop (0);
+      pthread_cleanup_combined_pop (0);
 
 
       /* Mark *once_control as having finished the initialization.  We need
diff --git a/nptl/tst-once5.cc b/nptl/tst-once5.cc
index b797ab3..60fe1ef 100644
--- a/nptl/tst-once5.cc
+++ b/nptl/tst-once5.cc
@@ -59,7 +59,7 @@ do_test (void)
                " throwing an exception", stderr);
     }
     catch (OnceException) {
-      if (1 < niter)
+      if (niter > 1)
         fputs ("pthread_once unexpectedly threw", stderr);
       result = 0;
     }
@@ -75,7 +75,5 @@ do_test (void)
   return result;
 }
 
-// The test currently hangs and is XFAILed.  Reduce the timeout.
-#define TIMEOUT 1
 #define TEST_FUNCTION do_test ()
 #include "../test-skeleton.c"