Re: [Qemu-devel] Re: [PATCH] fix smp with tcg mode and --enable-io-thread

[Alexander Graf]

On 22.06.2010, at 00:13, Jan Kiszka wrote:

> Jan Kiszka wrote:
>> And there is some race that cause a lock up in qemu_mutex_lock_iothread
>> after a while (the cpu_unlink_tb seems to race with the linking - just a
>> guess so far).
> 
> This seems to fix a long-standing race between cpu_exec and
> signal-driven cpu_unlink_tb:
> 
> diff --git a/cpu-exec.c b/cpu-exec.c
> index 026980a..bfc34e4 100644
> --- a/cpu-exec.c
> +++ b/cpu-exec.c
> @@ -599,8 +598,9 @@ int cpu_exec(CPUState *env1)
>                    TB, but before it is linked into a potentially
>                    infinite loop and becomes env->current_tb. Avoid
>                    starting execution if there is a pending interrupt. */
> -                if (!unlikely (env->exit_request)) {
> -                    env->current_tb = tb;
> +                env->current_tb = tb;
> +                asm("");

This is just barrier(), no?


Alex