[Crash-utility] [PATCH] Crash-Utility: s390x: Auto-detect the correct MAX_PHYSMEM_BITS used in vmcore being analyzed.

[Dave Anderson]

----- Original Message -----
> 
> 
> ----- Original Message -----
> 
> > > This would seem to be a little extreme.  If by chance CONFIG_SPARSEMEM
> > > is not configured, or for that matter, in old pre-sparsemem kernels,
> > > "mem_section" doesn't even exist as a symbol.  So there should be an
> > > IS_SPARSEMEM() qualifier to prevent the FATAL session-ending
> > > error.
> > > 
> > > I'm waiting for an s390x reservation as we speak, and I'll change
> > > (and test) the patch to do something like:
> > > 
> > >                if (IS_SPARSEMEM() &&
> > >                !set_s390x_max_physmem_bits())
> > >                        error(FATAL, ...
> > 
> > Actually that won't suffice, because the POST_GDB init call is done
> > before vm_init().  I'll add a new POST_VM case label to the s390x_init()
> > switch statement, and move the set_s390x_max_physmem_bits() call
> > there.
> 
> ... which won't work either, because vm_init() calls sparse_mem_init()
> which needs the MAX_PHYSMEM_BITS to be already set.
> 
> I guess we'll have to check for the existence of the mem_section array
> and preemptively/redundantly make the STRUCT_SIZE_INIT() call in your
> function so that we can still do it all POST_GDB.

And complicating matters even further, your patch presumes that the
kernel has configured CONFIG_SPARSEMEM_EXTREME in conjunction with 
CONFIG_SPARSEMEM.  Would it be possible for an s390x to be configured
with just CONFIG_SPARSEMEM alone?  If so, your patch breaks down.

Or is there another way you can determine which MAX_PHYSMEM_BITS value
is in use?

Dave