From ec9bd89fa48147e1d16e078217513c1235f9132a Mon Sep 17 00:00:00 2001 From: Olivier Hainque Date: Tue, 9 Apr 2013 18:06:54 +0200 Subject: Ensure good ordering of memory instruction in cpu_exec 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: Olivier Hainque Signed-off-by: Fabien Chouteau Reviewed-by: Paolo Bonzini Signed-off-by: Stefan Weil --- cpu-exec.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'cpu-exec.c') diff --git a/cpu-exec.c b/cpu-exec.c index e74e55656a..aa8fa893d9 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; } -- cgit v1.2.1