qom: aggressively optimize qom casting

[qemu.git] / cpu-exec.c

diff --git a/cpu-exec.c b/cpu-exec.c
index 235ddeed78f7e23f533967d99cd546c722bff26d..31c089dac0a7db66ac4d6270c293d1294bbc598a 100644 (file)
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -215,6 +215,14 @@ int cpu_exec(CPUArchState *env)
 
     cpu_single_env = env;
 
+    /* As long as cpu_single_env is null, up to the assignment just above,
+     * requests by other threads to exit the execution loop are expected to
+     * be issued using the exit_request global. We must make sure that our
+     * evaluation of the global value is performed past the cpu_single_env
+     * value transition point, which requires a memory barrier as well as
+     * an instruction scheduling constraint on modern architectures.  */
+    smp_mb();
+
     if (unlikely(exit_request)) {
         cpu->exit_request = 1;
     }