Fix a race situation for global variable dirtylimit_state.

Also, replace usleep by g_usleep to increase platform
accessibility to the sleep function.

Signed-off-by: Hyman Huang <yong.huang@smartx.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
---
 system/dirtylimit.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/system/dirtylimit.c b/system/dirtylimit.c
index fa959d7743..3666c4cb7c 100644
--- a/system/dirtylimit.c
+++ b/system/dirtylimit.c
@@ -411,12 +411,20 @@ void dirtylimit_set_all(uint64_t quota,
 
 void dirtylimit_vcpu_execute(CPUState *cpu)
 {
-    if (dirtylimit_in_service() &&
-        dirtylimit_vcpu_get_state(cpu->cpu_index)->enabled &&
-        cpu->throttle_us_per_full) {
-        trace_dirtylimit_vcpu_execute(cpu->cpu_index,
-                cpu->throttle_us_per_full);
-        usleep(cpu->throttle_us_per_full);
+    if (cpu->throttle_us_per_full) {
+        dirtylimit_state_lock();
+
+        if (dirtylimit_in_service() &&
+            dirtylimit_vcpu_get_state(cpu->cpu_index)->enabled) {
+            dirtylimit_state_unlock();
+            trace_dirtylimit_vcpu_execute(cpu->cpu_index,
+                    cpu->throttle_us_per_full);
+
+            g_usleep(cpu->throttle_us_per_full);
+            return;
+        }
+
+        dirtylimit_state_unlock();
     }
 }
 
-- 
2.39.1