Re: [PATCH v2 3/5] powerpc: Use preemption model accessors

On 16/11/21 14:41, Christophe Leroy wrote:

Le 10/11/2021 à 21:24, Valentin Schneider a écrit :

quoted

Per PREEMPT_DYNAMIC, checking CONFIG_PREEMPT doesn't tell you the actual
preemption model of the live kernel. Use the newly-introduced accessors
instead.

Is that change worth it for now ? As far as I can see powerpc doesn't
have DYNAMIC PREEMPT, a lot of work needs to be done before being able
to use it:
- Implement GENERIC_ENTRY
- Implement STATIC_CALLS (already done on PPC32, to be done on PPC64)

You're right, I ditched this patch for v3 - AFAICT the change wasn't even
valid as the preempt_schedule_irq() call needs to be replaced with
irqentry_exit_cond_resched() (IOW this needs to make use of the generic
entry code).

quoted

sched_init() -> preempt_dynamic_init() happens way before IRQs are set up,
so this should be fine.

It looks like you are mixing up interrupts and IRQs (also known as
"external interrupts").

ISI (Instruction Storage Interrupt) and DSI (Data Storage Interrupt) for
instance are also interrupts. They happen everytime there is a page
fault so may happen pretty early.

Traps generated by WARN_ON() are also interrupts that may happen at any
time.

Michael pointed this out and indeed triggering a WARN_ON() there is not
super smart. Thanks for teaching me a bit of what I'm putting my grubby
hands in :)