Use rel semantics of cas instead of acq semantics with full barrier before it in...

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.

diff --git a/ChangeLog b/ChangeLog
index 48b5d02..1e9df42 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,16 @@
+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.
+
 2009-07-16  Ulrich Drepper  <drepper@redhat.com>
 
        * sysdeps/generic/ldsodefs.h: Add prototype for

diff --git a/include/atomic.h b/include/atomic.h
index 9366f78..37d0111 100644 (file)
--- a/include/atomic.h
+++ b/include/atomic.h
@@ -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
 
 

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 70e4e58..0c0182e 100644 (file)
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -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).  */