[PATCH 13/29] powerpc/pseries/mobility: use stop_machine for join/suspend

[Michael Ellerman]

Hi Nathan,

Just a couple of nits ...

Nathan Lynch <nathanl at linux.ibm.com> writes:
> The partition suspend sequence as specified in the platform
> architecture requires that all active processor threads call
> H_JOIN, which:
...
> diff --git a/arch/powerpc/platforms/pseries/mobility.c b/arch/powerpc/platforms/pseries/mobility.c
> index 1b8ae221b98a..44ca7d4e143d 100644
> --- a/arch/powerpc/platforms/pseries/mobility.c
> +++ b/arch/powerpc/platforms/pseries/mobility.c
> @@ -412,6 +414,128 @@ static int wait_for_vasi_session_suspending(u64 handle)
...

> +
> +static int do_join(void *arg)
> +{
> +	atomic_t *counter = arg;
> +	long hvrc;
> +	int ret;
> +
> +	/* Must ensure MSR.EE off for H_JOIN. */
> +	hard_irq_disable();

Didn't stop_machine() already do that for us?

In the state machine in multi_cpu_stop().

> +	hvrc = plpar_hcall_norets(H_JOIN);
> +
> +	switch (hvrc) {
> +	case H_CONTINUE:
> +		/*
> +		 * All other CPUs are offline or in H_JOIN. This CPU
> +		 * attempts the suspend.
> +		 */
> +		ret = do_suspend();
> +		break;
> +	case H_SUCCESS:
> +		/*
> +		 * The suspend is complete and this cpu has received a
> +		 * prod.
> +		 */
> +		ret = 0;
> +		break;
> +	case H_BAD_MODE:
> +	case H_HARDWARE:
> +	default:
> +		ret = -EIO;
> +		pr_err_ratelimited("H_JOIN error %ld on CPU %i\n",
> +				   hvrc, smp_processor_id());
> +		break;
> +	}
> +
> +	if (atomic_inc_return(counter) == 1) {
> +		pr_info("CPU %u waking all threads\n", smp_processor_id());
> +		prod_others();
> +	}

Do we even need the counter? IIUC only one CPU receives H_CONTINUE. So
couldn't we just have that CPU do the prodding of others?

> +	/*
> +	 * Execution may have been suspended for several seconds, so
> +	 * reset the watchdog.
> +	 */
> +	touch_nmi_watchdog();
> +	return ret;
> +}
> +
> +static int pseries_migrate_partition(u64 handle)
> +{
> +	atomic_t counter = ATOMIC_INIT(0);
> +	int ret;
> +
> +	ret = wait_for_vasi_session_suspending(handle);
> +	if (ret)
> +		goto out;

Direct return would be clearer IMHO.

> +
> +	ret = stop_machine(do_join, &counter, cpu_online_mask);
> +	if (ret == 0)
> +		post_mobility_fixup();
> +out:
> +	return ret;
> +}
> +

cheers