Fix semaphore destruction (bug 12674).

This commit fixes semaphore destruction by either using 64b atomic
operations (where available), or by using two separate fields when only
32b atomic operations are available.  In the latter case, we keep a
conservative estimate of whether there are any waiting threads in one
bit of the field that counts the number of available tokens, thus
allowing sem_post to atomically both add a token and determine whether
it needs to call futex_wake.

See:
https://sourceware.org/ml/libc-alpha/2014-12/msg00155.html

1 files changed, 23 insertions, 1 deletions

diff --git a/sysdeps/nptl/internaltypes.h b/sysdeps/nptl/internaltypes.h
index 2f105459ee..7c0d2402a3 100644
--- a/sysdeps/nptl/internaltypes.h
+++ b/sysdeps/nptl/internaltypes.h
@@ -20,6 +20,8 @@
 #define _INTERNALTYPES_H	1
 
 #include <stdint.h>
+#include <atomic.h>
+#include <endian.h>
 
 
 struct pthread_attr
@@ -141,9 +143,29 @@ struct pthread_key_struct
 /* Semaphore variable structure.  */
 struct new_sem
 {
+#if __HAVE_64B_ATOMICS
+  /* The data field holds both value (in the least-significant 32 bytes) and
+     nwaiters.  */
+# if __BYTE_ORDER == __LITTLE_ENDIAN
+#  define SEM_VALUE_OFFSET 0
+# elif __BYTE_ORDER == __BIG_ENDIAN
+#  define SEM_VALUE_OFFSET 1
+# else
+# error Unsupported byte order.
+# endif
+# define SEM_NWAITERS_SHIFT 32
+# define SEM_VALUE_MASK (~(unsigned int)0)
+  unsigned long int data;
+  int private;
+  int pad;
+#else
+# define SEM_VALUE_SHIFT 1
+# define SEM_NWAITERS_MASK ((unsigned int)1)
   unsigned int value;
   int private;
-  unsigned long int nwaiters;
+  int pad;
+  unsigned int nwaiters;
+#endif
 };
 
 struct old_sem