[PATCH] Use rel semantics of cas instead of acq semantics withfull barrier before it in _int_free

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

The following patch fixes catomic_compare_and_exchange_*_rel definitions
(which were never used and weren't correct) and uses
catomic_compare_and_exchange_val_rel in _int_free.  Comparing to the
pre-2009-07-02 --enable-experimental-malloc state the generated code should
be identical on all arches other than ppc/ppc64 and on ppc/ppc64 should use
lwsync instead of isync barrier.

2009-07-13  Jakub Jelinek  <jakub@redhat.com>

	* include/atomic.h (catomic_compare_and_exchange_val_rel): If arch
	overrides atomic_compare_and_exchange_val_rel, define to
	atomic_compare_and_exchange_val_rel by default, otherwise default
	to catomic_compare_and_exchange_val_acq.
	(catomic_compare_and_exchange_bool_rel): If arch overrides
	atomic_compare_and_exchange_bool_rel, define to
	atomic_compare_and_exchange_bool_rel by default.
	* malloc/malloc.c (_int_free): Revert 2009-07-02 change.
	Use catomic_compare_and_exchange_val_rel instead of
	catomic_compare_and_exchange_val_acq.

--- libc/include/atomic.h.jj	2009-05-16 19:23:35.000000000 +0200
+++ libc/include/atomic.h	2009-07-13 17:47:02.000000000 +0200
@@ -107,14 +107,19 @@
 #endif
 
 
-#ifndef atomic_compare_and_exchange_val_rel
-# define atomic_compare_and_exchange_val_rel(mem, newval, oldval)	      \
-  atomic_compare_and_exchange_val_acq (mem, newval, oldval)
+#ifndef catomic_compare_and_exchange_val_rel
+# ifndef atomic_compare_and_exchange_val_rel
+#  define catomic_compare_and_exchange_val_rel(mem, newval, oldval)	      \
+  catomic_compare_and_exchange_val_acq (mem, newval, oldval)
+# else
+#  define catomic_compare_and_exchange_val_rel(mem, newval, oldval)	      \
+  atomic_compare_and_exchange_val_rel (mem, newval, oldval)
+# endif
 #endif
 
 
-#ifndef catomic_compare_and_exchange_val_rel
-# define catomic_compare_and_exchange_val_rel(mem, newval, oldval)	      \
+#ifndef atomic_compare_and_exchange_val_rel
+# define atomic_compare_and_exchange_val_rel(mem, newval, oldval)	      \
   atomic_compare_and_exchange_val_acq (mem, newval, oldval)
 #endif
 
@@ -155,15 +160,20 @@
 #endif
 
 
-#ifndef atomic_compare_and_exchange_bool_rel
-# define atomic_compare_and_exchange_bool_rel(mem, newval, oldval) \
-  atomic_compare_and_exchange_bool_acq (mem, newval, oldval)
+#ifndef catomic_compare_and_exchange_bool_rel
+# ifndef atomic_compare_and_exchange_bool_rel
+#  define catomic_compare_and_exchange_bool_rel(mem, newval, oldval)	      \
+  catomic_compare_and_exchange_bool_acq (mem, newval, oldval)
+# else
+#  define catomic_compare_and_exchange_bool_rel(mem, newval, oldval)	      \
+  atomic_compare_and_exchange_bool_rel (mem, newval, oldval)
+# endif
 #endif
 
 
-#ifndef catomic_compare_and_exchange_bool_rel
-# define catomic_compare_and_exchange_bool_rel(mem, newval, oldval) \
-  catomic_compare_and_exchange_bool_acq (mem, newval, oldval)
+#ifndef atomic_compare_and_exchange_bool_rel
+# define atomic_compare_and_exchange_bool_rel(mem, newval, oldval) \
+  atomic_compare_and_exchange_bool_acq (mem, newval, oldval)
 #endif
 
 
--- libc/malloc/malloc.c.jj	2009-07-07 19:10:19.000000000 +0200
+++ libc/malloc/malloc.c	2009-07-13 17:47:52.000000000 +0200
@@ -4822,9 +4822,8 @@ _int_free(mstate av, mchunkptr p)
 	    goto errout;
 	  }
 	p->fd = fd = old;
-	atomic_full_barrier ();
       }
-    while ((old = catomic_compare_and_exchange_val_acq (fb, p, fd)) != fd);
+    while ((old = catomic_compare_and_exchange_val_rel (fb, p, fd)) != fd);
 #else
     /* Another simple check: make sure the top of the bin is not the
        record we are going to add (i.e., double free).  */

	Jakub