From: Olivier Hainque <hain...@adacore.com>
The IO thread, when it senses cpu_single_env == 0, expects exit_request
to be checked later on. A compiler scheduling constraint is not strong
enough to ensure this on modern architecture. A memory fence is needed
as well.
Signed-off-by: Fabien Chouteau <chout...@adacore.com>
---
cpu-exec.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/cpu-exec.c b/cpu-exec.c
index e74e556..aa8fa89 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -217,6 +217,14 @@ 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;
}
--
1.7.9.5
