Re: [PATCH/RFC] I/O-check interface for driver's error handling

[Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>]

Matthew Wilcox wrote:
> I think what Jeff meant was "this new API handles none of this".
> And that's true, it doesn't handle DMA errors.  But I think that's just
> something that hasn't been written/designed yet.

Yes, this API just supports drivers wanting to be more RAS-aware.
It would be happy if how implement it could be separate in two part:
  - arch-specific part
     Capability would depend on arch, can only generic thing but couldn't
     be device specific. Device/bus isolation could be(with help of hotplug
     and so on), but re-enable them would not be easily.
  - generic part
     Capability would depend on drivers, should be more device specific.
How divide and connect them is now in discussion and consideration.

> So how should we handle it?  Obviously the driver may not be executing
> when a PCI parity error occurs, so we probably get to find out about
> this through some architecture-specific whole-system error, let's call
> it an MCA.
> 
> The MCA handler has to go and figure out what the hell just happened
> (was it a DIMM error, PCI bus error, etc).  OK, fine, it finds that it
> was an error on PCI bus 73.  At this point, I think the architecture
> error handler needs to call into the PCI subsystem and say "Hey, there
> was an error, you deal with it".
> 
> If we're lucky, we get all the information that allows us to figure
> out which device it was (eg a destination address that matches a BAR),
> then we could have a ->error method in the pci_driver that handles it.
> If there's no ->error method, at leat call ->remove so one device only
> takes itself down.
> 
> Does this make sense?

Note that here is a difficulty: the MCA handler on some arch would run on
special context - MCA environment. In other words, since some MCA handler
would be called by non-maskable interrupt(e.g. NMI), so it's difficult to
call some driver's callback using protected kernel locks from MCA context.

Therefore what MCA handler could do is just indicates a error was there,
by something like status flag which drivers can refer. And after possible
deley, we would be able to call callbacks.


Thanks,
H.Seto