Re: [RFC PATCH 02/19] system/cpus: Only kick running vCPUs

[Richard Henderson]

On 6/6/25 17:44, Philippe Mathieu-Daudé wrote:
> As an optimization, avoid kicking stopped vCPUs.
>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
>   system/cpus.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/system/cpus.c b/system/cpus.c
> index d16b0dff989..4835e5ced48 100644
> --- a/system/cpus.c
> +++ b/system/cpus.c
> @@ -494,6 +494,11 @@ void cpus_kick_thread(CPUState *cpu)
>   void qemu_cpu_kick(CPUState *cpu)
>   {
>       qemu_cond_broadcast(cpu->halt_cond);
> +
> +    if (!cpu_can_run(cpu)) {
> +        return;
> +    }
> +
This would appear to be a race condition.  The evaluation of cpu_can_run should be done 
within the context of 'cpu', not here, and not *after* we've already woken 'cpu' via the 
broadcast.

r~