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

[Don Zickus <dzickus@redhat.com>]

On Mon, Oct 17, 2011 at 09:56:50AM -0700, Luck, Tony wrote:
> > All this lock busting probably isn't pretty and causes one to reflect what
> > is going on here.  But as long as we are going to keep the kmsg_dump
> > design, changes like this seem necessary to make sure the locking stays
> > sane(r) for now.
> 
> So should we let the back-end know that locks have been busted?  I worry
> that we'll get through the pstore layer by blasting away at any locks that
> get in our way - but then the backend (which may well have been written on
> the assumption that pstore serialized calls to it) will not do anything
> useful (and may cause its own hang).

I was kinda alluding to something like that, when I said we probably need
follow on patches to clean up the backend.  But maybe it would be smarter
to set a flag in pstore to let the backend know we busted the locks
instead of letting them do panic checks themselves.  I agree with your
concerns.

I really can't think of a good overall solution other than slowly
step-by-step untangle things by making subtle changes, this round being
the serialization of kmsg_dump().

My brain is to small to figure this out.  I keep thinking about making an
ascii art diagram to see all the various paths and their contexts, but
then I keep finding more interesting things to do. :-)

Perhaps we should do that and make some rules about what the back-end can
and can not do when plugging into kmsg_dump.

Cheers,
Don