Re: [PATCH] PCI / PM: Allow runtime PM without callback functions

[Jarkko Nikula <jarkko.nikula@linux.intel.com>]

On 10/20/2018 07:19 PM, Bjorn Helgaas wrote:
> On Fri, Oct 19, 2018 at 03:21:05PM +0200, Jean Delvare wrote:
>> Later in this function, pm is dereferenced again. It happens twice in
>> the "if (error)" condition where it is currently safe (error can't be
>> non-zero if pm->runtime_suspend() has not been called, and obviously
>> pm->runtime_suspend() can't have been called if pm was NULL). However
>> it also happens later without the condition:
>>
>> 	if (!pci_dev->state_saved && pci_dev->current_state != PCI_D0
>> 	    && pci_dev->current_state != PCI_UNKNOWN) {
>> 		WARN_ONCE(pci_dev->current_state != prev,
>> 			"PCI PM: State of device not saved by %pF\n",
>> 			pm->runtime_suspend);
>> 		return 0;
>> 	}
>>
>> I am no expert of the PM framework but is there no risk to dereference
>> NULL at this point? Or even if pm is non-NULL, pm->runtime_suspend may
>> be NULL, leading to a confusing warning message?
>>
Thanks for spotting this! I don't have any excuse why I was so 
completely blind.

>> More generally, I would feel better if instead of initializing error to
>> 0, we would move under the "if (pm && pm->runtime_suspend)" condition
>> everything that must not be run if pm->runtime_suspend is not defined.
>> That would make the possible code flows a lot clearer.
> 
> I agree, this isn't good.  Even if it's safe (and I don't think that
> second spot is safe), it's too hard to analyze.  I'm going to drop
> this for now.
> 
Thanks. I'll cook a better version.

-- 
Jarkko