I was just now trying to track down my other issue, whereby somewhere
along the tree kexec stops working properly. In the process of doing
that I realized I had initially made one change to the original 4.9
config beyond oldconfig: I'd turned off WX debugging.

I've now compiled a bunch of versions with WX debugging back on, and
new behavior arises. I am attaching the joournalctl log of a booted
4.13 kernel (from Linus' tree, commit 569dbb8).

It boots and logs me in, but returns a call trace I wasn't seeing
without the WX debugging. I am sending over in case it provides any
information.

The trace bears the 23:24:09 timestamp.

On Sat, Dec 23, 2017 at 01:35:12AM +0000, Dexuan Cui wrote:
> > From: Alexandru Chirvasitu [mailto:achirvasub@gmail.com]
> > Sent: Friday, December 22, 2017 14:29
> > 
> > The output of that precise command run just now on a freshly-compiled
> > copy of that commit is attached.
> > 
> > On Fri, Dec 22, 2017 at 09:31:28PM +0000, Dexuan Cui wrote:
> > > > From: Alexandru Chirvasitu [mailto:achirvasub@gmail.com]
> > > > Sent: Friday, December 22, 2017 06:21
> > > >
> > > > In the absence of logs, the best I can do at the moment is attach a
> > > > picture of the screen I am presented with on the apic=debug boot
> > > > attempt.
> > > > Alex
> > >
> > > The panic happens in irq_matrix_assign_system+0x4e/0xd0 in your picture.
> > > IMO we should find which line of code causes the panic. I suppose
> > > "objdump -D kernel/irq/matrix.o" can help to do that.
> > >
> > > Thanks,
> > > -- Dexuan
> 
> The BUG_ON panic happens at line 147:
>                    BUG_ON(!test_and_clear_bit(bit, cm->alloc_map));
> 
> I'm sure Thomas and Dou know it better than me. 
> 
> 137 void irq_matrix_assign_system(struct irq_matrix *m, unsigned int bit,
> 138                               bool replace)
> 139 {
> 140         struct cpumap *cm = this_cpu_ptr(m->maps);
> 141
> 142         BUG_ON(bit > m->matrix_bits);
> 143         BUG_ON(m->online_maps > 1 || (m->online_maps && !replace));
> 144
> 145         set_bit(bit, m->system_map);
> 146         if (replace) {
> 147                 BUG_ON(!test_and_clear_bit(bit, cm->alloc_map));
> 148                 cm->allocated--;
> 149                 m->total_allocated--;
> 150         }
> 151         if (bit >= m->alloc_start && bit < m->alloc_end)
> 152                 m->systembits_inalloc++;
> 153
> 154         trace_irq_matrix_assign_system(bit, m);
> 155 }
> 
> -- Dexuan
>