On Wed, Mar 29, 2017 at 10:39:11AM -0700, Doug Berger wrote:
> On 03/29/2017 03:13 AM, Mark Rutland wrote:
> >> +static int dump_gisb_error(struct notifier_block *self, unsigned long v,
> >> + void *p)
> >> + return 0;
> >
> > I think this should be NOTIFY_OK.
> >
> I used dump_mem_limit() as a template and didn't catch this (work to
> do...). Upon review I think I would prefer NOTIFY_DONE since this call
> is opportunistic (i.e. it is taking the opportunity to check whether
> additional diagnostic data is available to display) and has no interest
> in affecting the overall handling of the event.
That's fine by me.
Does the distinction matter here?
Most notifer users treat NOTIFY_OK and NOTIFY_DONE as equivalent, and
notifier_call_chain only terminates when it sees NOTIFY_STOP_MASK.
[...]
> >> + if (list_is_singular(&brcmstb_gisb_arb_device_list)) {
> >> + register_die_notifier(&gisb_error_notifier);
> >> + atomic_notifier_chain_register(&panic_notifier_list,
> >> + &gisb_error_notifier);
> >
> > I don't think this is quite right. A notifier_block can only be
> > registered to one notifier chain at a time, and this has the potential
> > to corrupt both chains.
> >
> A VERY good point thanks for pointing this out.
>
> > I also think you only need to register the panic notifier. An SError
> > should always result in a panic.
> >
> That was my initial thought as well. However, testing revealed that the
> bad mode Oops actually exits the user space process and doesn't reach
> the panic so there was no helpful diagnostic message. This may be in
> line with your comments about insufficient fatality of failures in PATCH
> v2 6/8, but it actually is more in line with our desired behavior for
> the aborted write. Setting the notify on die gave us the result we are
> looking for, but as noted above I should have created a separate notifier.
>
> I had hoped that the same approach (i.e. die notifier) would remove the
> need for PATCH v2 6/8 as well, but I found that the Unhandled fault
> error didn't actually die from user mode.
In my mind it's a bug that we don't treat those errors more fatally.
I'll try to dig into that.
Thanks,
Mark.
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