Re: [PATCH kvm-unit-tests v1 5/6] s390x: smp: Create and use a non-waiting CPU restart

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Thu,  3 Mar 2022 22:04:24 +0100
Eric Farman <farman@linux.ibm.com> wrote:

> The kvm-unit-tests infrastructure for a CPU restart waits for the
> SIGP RESTART to complete. In order to test the restart itself,
> create a variation that does not wait, and test the state of the
> CPU directly.
> 
> While here, add some better report prefixes/messages, to clarify
> which condition is being examined (similar to test_stop_store_status()).
> 
> Signed-off-by: Eric Farman <farman@linux.ibm.com>
> ---
>  lib/s390x/smp.c | 22 ++++++++++++++++++++++
>  lib/s390x/smp.h |  1 +
>  s390x/smp.c     | 18 +++++++++++++++---
>  3 files changed, 38 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/s390x/smp.c b/lib/s390x/smp.c
> index 84e536e8..85b046a5 100644
> --- a/lib/s390x/smp.c
> +++ b/lib/s390x/smp.c
> @@ -192,6 +192,28 @@ int smp_cpu_restart(uint16_t idx)
>  	return rc;
>  }
>  
> +/*
> + * Functionally equivalent to smp_cpu_restart(), but without the
> + * elements that wait/serialize matters here in the test.
> + * Used to see if KVM itself is serialized correctly.
> + */
> +int smp_cpu_restart_nowait(uint16_t idx)
> +{
> +	spin_lock(&lock);
> +
> +	/* Don't suppress a CC2 with sigp_retry() */
> +	if (smp_sigp(idx, SIGP_RESTART, 0, NULL)) {
> +		spin_unlock(&lock);
> +		return -1;
> +	}
> +
> +	cpus[idx].active = true;
> +
> +	spin_unlock(&lock);
> +
> +	return 0;
> +}
> +
>  int smp_cpu_start(uint16_t idx, struct psw psw)
>  {
>  	int rc;
> diff --git a/lib/s390x/smp.h b/lib/s390x/smp.h
> index bae03dfd..24a0e2e0 100644
> --- a/lib/s390x/smp.h
> +++ b/lib/s390x/smp.h
> @@ -42,6 +42,7 @@ uint16_t smp_cpu_addr(uint16_t idx);
>  bool smp_cpu_stopped(uint16_t idx);
>  bool smp_sense_running_status(uint16_t idx);
>  int smp_cpu_restart(uint16_t idx);
> +int smp_cpu_restart_nowait(uint16_t idx);
>  int smp_cpu_start(uint16_t idx, struct psw psw);
>  int smp_cpu_stop(uint16_t idx);
>  int smp_cpu_stop_nowait(uint16_t idx);
> diff --git a/s390x/smp.c b/s390x/smp.c
> index 11c2c673..03160b80 100644
> --- a/s390x/smp.c
> +++ b/s390x/smp.c
> @@ -55,23 +55,35 @@ static void test_restart(void)
>  	struct cpu *cpu = smp_cpu_from_idx(1);
>  	struct lowcore *lc = cpu->lowcore;
>  
> +	report_prefix_push("restart");
> +	report_prefix_push("stopped");
> +
>  	lc->restart_new_psw.mask = extract_psw_mask();
>  	lc->restart_new_psw.addr = (unsigned long)test_func;
>  
>  	/* Make sure cpu is stopped */
>  	smp_cpu_stop(1);
>  	set_flag(0);
> -	smp_cpu_restart(1);
> +	smp_cpu_restart_nowait(1);
> +	report(!smp_cpu_stopped(1), "cpu started");

can this check ^ race?
we are using the flag to check if the CPU actually restarts, right?

>  	wait_for_flag();
> +	report_pass("test flag");
> +
> +	report_prefix_pop();
> +	report_prefix_push("running");
>  
>  	/*
>  	 * Wait until cpu 1 has set the flag because it executed the
>  	 * restart function.
>  	 */
>  	set_flag(0);
> -	smp_cpu_restart(1);
> +	smp_cpu_restart_nowait(1);
> +	report(!smp_cpu_stopped(1), "cpu started");

same here

>  	wait_for_flag();
> -	report_pass("restart while running");
> +	report_pass("test flag");
> +
> +	report_prefix_pop();
> +	report_prefix_pop();
>  }
>  
>  static void test_stop(void)