Re: [PATCH 1/2] x86/cpu/topology: don't write to immutable cpu_present_mask

[Ingo Molnar <mingo@kernel.org>]

* Thomas Gleixner <tglx@linutronix.de> wrote:

> On Sun, Apr 07 2024 at 18:26, Alexey Dobriyan wrote:
> > Workaround the following oops:
> >
> > 	topology_hotplug_apic
> > 	topo_set_cpuids
> > 		set_cpu_possible(cpu, true);
> > 		// write to __ro_after_init section after init
> 
> Duh, yes.
> 
> > adobriyan: I'm not sure what's going on, can it set unset bit here?
> > If not, then why does it repeat the job and set already set bits.
> >
> > Anyhow, let's not oops peoples' machines for now.
> 
> Adding a bandaid to paper over the non-understood real problem is
> definitely not a good plan. I take this patch as a bug report.
> 
> Proper fix below.

BTW., independently of the fix, warning about a too late set_cpu_possible() 
might still make sense - clearly it *can* be called too late by 
architecture init code :-)

It's not a performance-sensitive function in any case, so the extra 
debugging code might not hurt.

Thanks,

	Ingo