Re: [RFC PATCH 06/13] arm64: percpu: Add infrastructure for preemptible this_cpu_*() ops

[Peter Zijlstra]

On Tue, Jul 28, 2026 at 04:19:58PM +0200, Peter Zijlstra wrote:
> On Tue, Jul 28, 2026 at 01:38:52PM +0100, Mark Rutland wrote:
> 
> > With the scheme added in this patch, this can be compiled as:
> > 
> > | <outline_this_cpu_add_u64>:
> > |        mrs     x2, sp_el0
> > |        mov     x4, #0xc80
> > |        strh    w4, [x2, #20]
> > |        mrs     x4, tpidr_el1
> > |        add     x3, x0, x4
> 
> Which it then recomputes, and so is harmless.

Here!

> > | 1:     ldxr    x6, [x3]
> > |        add     x6, x6, x1
> > |        stxr    w5, x6, [x3]
> > |        cbnz    w5, 1b
> 
> If we get here and interrupts happens, we recompute pointlessly, no harm
> done.
> 
> Anyway, per this sequence there is no point in ever doing the fixup. So
> perhaps give a better example?

Nevermind, brain just wasn't working right, when interrupt happens at
'Here!' above, it needs the fixup, irrespective of the atomic type.

> > |        strh    wzr, [x2, #20]
> > |        ret