[RFC PATCH 04/10] preempt: use atomic_t to for preempt_count

[Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>]

This ensures that preempt_count will be accounted correctly
during in-hypevisor context switches.

Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
---
 xen/common/preempt.c      | 6 +++---
 xen/include/xen/preempt.h | 9 ++++-----
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/xen/common/preempt.c b/xen/common/preempt.c
index 3b4178fd44..ad61c8419a 100644
--- a/xen/common/preempt.c
+++ b/xen/common/preempt.c
@@ -23,17 +23,17 @@
 #include <xen/irq.h>
 #include <asm/system.h>
 
-DEFINE_PER_CPU(unsigned int, __preempt_count);
+DEFINE_PER_CPU(atomic_t, __preempt_count);
 
 bool_t in_atomic(void)
 {
-    return preempt_count() || in_irq() || !local_irq_is_enabled();
+    return atomic_read(&preempt_count()) || in_irq() || local_irq_is_enabled();
 }
 
 #ifndef NDEBUG
 void ASSERT_NOT_IN_ATOMIC(void)
 {
-    ASSERT(!preempt_count());
+    ASSERT(!atomic_read(&preempt_count()));
     ASSERT(!in_irq());
     ASSERT(local_irq_is_enabled());
 }
diff --git a/xen/include/xen/preempt.h b/xen/include/xen/preempt.h
index bef83135a1..e217900d6e 100644
--- a/xen/include/xen/preempt.h
+++ b/xen/include/xen/preempt.h
@@ -9,21 +9,20 @@
 #ifndef __XEN_PREEMPT_H__
 #define __XEN_PREEMPT_H__
 
+#include <asm/atomic.h>
 #include <xen/types.h>
 #include <xen/percpu.h>
 
-DECLARE_PER_CPU(unsigned int, __preempt_count);
+DECLARE_PER_CPU(atomic_t, __preempt_count);
 
 #define preempt_count() (this_cpu(__preempt_count))
 
 #define preempt_disable() do {                  \
-    preempt_count()++;                          \
-    barrier();                                  \
+    atomic_inc(&preempt_count());               \
 } while (0)
 
 #define preempt_enable() do {                   \
-    barrier();                                  \
-    preempt_count()--;                          \
+    atomic_dec(&preempt_count());               \
 } while (0)
 
 bool_t in_atomic(void);
-- 
2.29.2