Subject: Re: [PATCH] powerpc/eeh: Fix wrong flag passed to eeh_unfreeze_pe()

From: Gavin Shan <[email-masked]>
Date: Thu, 19 Jan 2017 09:50:38 +1100

On Wed, Jan 18, 2017 at 04:49:58PM +1100, Michael Ellerman wrote:
>Gavin Shan <[email-masked]> writes:
>
>> In __eeh_clear_pe_frozen_state(), we should pass the flag's value
>> instead of its address to eeh_unfreeze_pe(). This doesn't introduce
>> any problems, but the code is just wrong.
>
>It means any caller that passes false, will be getting the wrong
>behaviour. eg. I see at least one call in eeh_reset_device() which
>passes false to eeh_clear_pe_frozen_state(), which is then passed to
>__eeh_clear_pe_frozen_state().
>

Yes, when __eeh_clear_pe_frozen_state() succeeds on all child PEs, the
isolated flag is cleared. No failure from __eeh_clear_pe_frozen_state()
was observed previously.

>But I guess you're saying that caller doesn't actually see a bug because
>of this?
>

Yes, I'll update the changelog accordingly, to give more details as above.

>> This fixes the code by passing flag's value to eeh_unfreeze_pe().
>>
>> Cc: [email-masked] #3.18+
>> Fixes: 5cfb20b96f6 ("powerpc/eeh: Emulate EEH recovery for VFIO devices")
>> Signed-off-by: Gavin Shan <[email-masked]>
>>
>> diff --git a/arch/powerpc/kernel/eeh_driver.c b/arch/powerpc/kernel/eeh_driver.c
>> index d88573b..fa15fa6 100644
>> --- a/arch/powerpc/kernel/eeh_driver.c
>> +++ b/arch/powerpc/kernel/eeh_driver.c
>> @@ -549,7 +549,7 @@ static void *__eeh_clear_pe_frozen_state(void *data, void *flag)
>
>	bool *clear_sw_state = flag;
>
>>  	int i, rc = 1;
>>  
>>  	for (i = 0; rc && i < 3; i++)
>> -		rc = eeh_unfreeze_pe(pe, clear_sw_state);
>> +		rc = eeh_unfreeze_pe(pe, *clear_sw_state);
>
>
>I think it would be better to just do the dereference once:
>
>	bool clear_sw_state = *(bool *)flag;
>	int i, rc = 1;
>
>	for (i = 0; rc && i < 3; i++)
>		rc = eeh_unfreeze_pe(pe, clear_sw_state);
>

Thanks, Michael. I'll update in v2.

Thanks,
Gavin