[Xen-devel] [PATCHv1 1/4] atomic: replace atomic_compareandswap() with atomic_cmpxchg()

[David Vrabel <david.vrabel@xxxxxxxxxx>]

atomic_compareandswap() used atomic_t as the new, old and returned
values which is less convinient than using just int.

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
 xen/common/domain.c          |  5 +----
 xen/include/asm-arm/atomic.h |  8 --------
 xen/include/asm-x86/atomic.h |  8 --------
 xen/include/xen/atomic.h     | 43 +++++++++++++++++++++++++++++++++++++++++++
 xen/include/xen/sched.h      | 11 +++++------
 5 files changed, 49 insertions(+), 26 deletions(-)
 create mode 100644 xen/include/xen/atomic.h

diff --git a/xen/common/domain.c b/xen/common/domain.c
index c4661d8..3960f06 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -851,14 +851,11 @@ static void complete_domain_destroy(struct rcu_head *head)
 void domain_destroy(struct domain *d)
 {
     struct domain **pd;
-    atomic_t old = ATOMIC_INIT(0);
-    atomic_t new = ATOMIC_INIT(DOMAIN_DESTROYED);
 
     BUG_ON(!d->is_dying);
 
     /* May be already destroyed, or get_domain() can race us. */
-    old = atomic_compareandswap(old, new, &d->refcnt);
-    if ( _atomic_read(old) != 0 )
+    if ( atomic_cmpxchg(&d->refcnt, 0, DOMAIN_DESTROYED) != 0 )
         return;
 
     cpupool_rm_domain(d);
diff --git a/xen/include/asm-arm/atomic.h b/xen/include/asm-arm/atomic.h
index 5a38c67..29ab265 100644
--- a/xen/include/asm-arm/atomic.h
+++ b/xen/include/asm-arm/atomic.h
@@ -138,14 +138,6 @@ static inline void _atomic_set(atomic_t *v, int i)
 # error "unknown ARM variant"
 #endif
 
-static inline atomic_t atomic_compareandswap(
-    atomic_t old, atomic_t new, atomic_t *v)
-{
-    atomic_t rc;
-    rc.counter = __cmpxchg(&v->counter, old.counter, new.counter, sizeof(int));
-    return rc;
-}
-
 #endif /* __ARCH_ARM_ATOMIC__ */
 /*
  * Local variables:
diff --git a/xen/include/asm-x86/atomic.h b/xen/include/asm-x86/atomic.h
index 2b8c877..a40319e 100644
--- a/xen/include/asm-x86/atomic.h
+++ b/xen/include/asm-x86/atomic.h
@@ -272,12 +272,4 @@ static inline int atomic_add_negative(int i, atomic_t *v)
     return c;
 }
 
-static inline atomic_t atomic_compareandswap(
-    atomic_t old, atomic_t new, atomic_t *v)
-{
-    atomic_t rc;
-    rc.counter = __cmpxchg(&v->counter, old.counter, new.counter, sizeof(int));
-    return rc;
-}
-
 #endif /* __ARCH_X86_ATOMIC__ */
diff --git a/xen/include/xen/atomic.h b/xen/include/xen/atomic.h
new file mode 100644
index 0000000..387ac04
--- /dev/null
+++ b/xen/include/xen/atomic.h
@@ -0,0 +1,43 @@
+/******************************************************************************
+ * atomic.h
+ *
+ * Generic atomic variables.
+ *
+ * Copyright (c) 2015 Citrix R&D Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef __ATOMIC_H__
+#define __ATOMIC_H__
+
+#include <asm/atomic.h>
+
+static inline int atomic_cmpxchg(atomic_t *v, int old, int new)
+{
+    return cmpxchg(&v->counter, old, new);
+}
+
+/**
+ * atomic_add_return - add integer and return
+ * @i: integer value to add
+ * @v: pointer of type atomic_t
+ *
+ * Atomically adds @i to @v and returns @i + @v
+ */
+static inline int atomic_add_return(int i, atomic_t *v)
+{
+    return i + arch_fetch_and_add(&v->counter, i);
+}
+
+#endif /* __ATOMIC_H__ */
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 3729b0f..cca5547 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -17,7 +17,7 @@
 #include <xen/mm.h>
 #include <xen/smp.h>
 #include <xen/perfc.h>
-#include <asm/atomic.h>
+#include <xen/atomic.h>
 #include <xen/wait.h>
 #include <public/xen.h>
 #include <public/domctl.h>
@@ -481,16 +481,15 @@ extern struct vcpu *idle_vcpu[NR_CPUS];
  */
 static always_inline int get_domain(struct domain *d)
 {
-    atomic_t old, new, seen = d->refcnt;
+    int old, seen = atomic_read(&d->refcnt);
     do
     {
         old = seen;
-        if ( unlikely(_atomic_read(old) & DOMAIN_DESTROYED) )
+        if ( unlikely(old & DOMAIN_DESTROYED) )
             return 0;
-        _atomic_set(&new, _atomic_read(old) + 1);
-        seen = atomic_compareandswap(old, new, &d->refcnt);
+        seen = atomic_cmpxchg(&d->refcnt, old, old + 1);
     }
-    while ( unlikely(_atomic_read(seen) != _atomic_read(old)) );
+    while ( unlikely(seen != old) );
     return 1;
 }
 
-- 
2.1.4


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