Re: [PATCH] irqchip/gic-v3-its: Don't acquire rt_spin_lock in allocate_vpe_l1_table()

On Fri, Jan 09 2026 at 16:13, Marc Zyngier wrote:

On Thu, 08 Jan 2026 22:11:33 +0000,
Thomas Gleixner [off-list ref] wrote:

quoted

At the point where a CPU is brought up, the topology should be known
already, which means this can be allocated on the control CPU _before_
the new CPU comes up, no?

No. Each CPU finds *itself* in the forest of redistributors, and from
there tries to find whether it has some shared resource with a CPU
that has booted before it. That's because firmware is absolutely awful
and can't present a consistent view of the system.

Groan....

Anyway, I expect it could be solved by moving this part of the init to
an ONLINE HP callback.

Which needs to be before CPUHP_AP_IRQ_AFFINITY_ONLINE, but even that
might be to late because there are callbacks in the STARTING section,
i.e. timer, perf, which might rely on interrupts being accessible.

Also that patch seems to be incomplete because there is another
allocation further down in allocate_vpe_l1_table()....

Thanks,

        tglx