Subject: Re: [PATCH v2 1/2] powerpc/eeh: fix pseries_eeh_configure_bridge()

From: Nathan Lynch <[email-masked]>
Date: Tue, 21 Apr 2020 18:33:36 -0500

Sam Bobroff <[email-masked]> writes:
> If a device is hot unplgged during EEH recovery, it's possible for the
> RTAS call to ibm,configure-pe in pseries_eeh_configure() to return
> parameter error (-3), however negative return values are not checked
> for and this leads to an infinite loop.
>
> Fix this by correctly bailing out on negative values.
>
> Signed-off-by: Sam Bobroff <[email-masked]>
> ---
>  arch/powerpc/platforms/pseries/eeh_pseries.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/platforms/pseries/eeh_pseries.c b/arch/powerpc/platforms/pseries/eeh_pseries.c
> index 893ba3f562c4..c4ef03bec0de 100644
> --- a/arch/powerpc/platforms/pseries/eeh_pseries.c
> +++ b/arch/powerpc/platforms/pseries/eeh_pseries.c
> @@ -605,7 +605,7 @@ static int pseries_eeh_configure_bridge(struct eeh_pe *pe)
>  				config_addr, BUID_HI(pe->phb->buid),
>  				BUID_LO(pe->phb->buid));
>  
> -		if (!ret)
> +		if (ret <= 0)
>  			return ret;

Note that this returns the firmware error value (e.g. -3 parameter
error) without converting it to a Linux errno. Nothing checks the error
value of this function as best I can tell, but -EINVAL would be better
than an implicit -ESRCH here.

And while this will behave correctly, the pr_warn() at the end of
pseries_eeh_configure_bridge() hints that someone had the intention
that this code should log a message on such an error:

static int pseries_eeh_configure_bridge(struct eeh_pe *pe)
{
	int config_addr;
	int ret;
	/* Waiting 0.2s maximum before skipping configuration */
	int max_wait = 200;

	/* Figure out the PE address */
	config_addr = pe->config_addr;
	if (pe->addr)
		config_addr = pe->addr;

	while (max_wait > 0) {
		ret = rtas_call(ibm_configure_pe, 3, 1, NULL,
				config_addr, BUID_HI(pe->phb->buid),
				BUID_LO(pe->phb->buid));

		if (!ret)
			return ret;

		/*
		 * If RTAS returns a delay value that's above 100ms, cut it
		 * down to 100ms in case firmware made a mistake.  For more
		 * on how these delay values work see rtas_busy_delay_time
		 */
		if (ret > RTAS_EXTENDED_DELAY_MIN+2 &&
		    ret <= RTAS_EXTENDED_DELAY_MAX)
			ret = RTAS_EXTENDED_DELAY_MIN+2;

		max_wait -= rtas_busy_delay_time(ret);

		if (max_wait < 0)
			break;

		rtas_busy_delay(ret);
	}

	pr_warn("%s: Unable to configure bridge PHB#%x-PE#%x (%d)\n",
		__func__, pe->phb->global_number, pe->addr, ret);
	return ret;
}

So perhaps the error path should be made to break out of the loop
instead of returning. Or is the parameter error result simply
uninteresting in this scenario?