Re: [RFC][PATCH -next] make pstore/kmsg_dump run after stopping other cpus in panic path

[Don Zickus <dzickus@redhat.com>]

On Tue, Oct 18, 2011 at 10:52:22AM -0400, Seiji Aguchi wrote:
> Hi,
> 
> >> afacit this assumes that (reason == KMSG_DUMP_PANIC) if in_nmi().  Is
> >> that always the case, and will it always be the case in the future?
> >
> 
> Currently, when kernel is in nmi context and kmsg_dump() are called, its reason is always "KMSG_DUMP_PANIC".
> 
> >
> >Perhaps a 'BUG_ON(in_nmi() && reason != KMSG_DUMP_PANIC)'?
> 
> I don't think BUG_ON() is needed.
> 
> If someone would like to log messages in the case of "in_nmi() && reason != KMSG_DUMP_PANIC",
> he/she will add a new trigger as follows.

The point I was trying to make with the BUG_ON is to catch future uses of
NMI and kmsg_dump that were implemented without understanding the
restriction we place (you have to be in a panic path for NMI to use
pstore/kmsg_dump).

That is part of the wider problem with kmsg_dump that Vivek talks about
with me, is that it is just a giant hook in the panic path with limited
auditing.  So we need to explicit set our expectations with BUG_ONs/WARNs
otherwise we might get bit later by them.

Cheers,
Don