[PATCH RFC v2 03/10] locking/local_lock: Introduce localtry_lock_t

[Davidlohr Bueso]

On Fri, 14 Feb 2025, Vlastimil Babka wrote:

>From: Sebastian Andrzej Siewior <bigeasy at linutronix.de>
>
>In !PREEMPT_RT local_lock_irqsave() disables interrupts to protect
>critical section, but it doesn't prevent NMI, so the fully reentrant
>code cannot use local_lock_irqsave() for exclusive access.
>
>Introduce localtry_lock_t and localtry_lock_irqsave() that
>disables interrupts and sets acquired=1, so localtry_lock_irqsave()
>from NMI attempting to acquire the same lock will return false.
>
>In PREEMPT_RT local_lock_irqsave() maps to preemptible spin_lock().
>Map localtry_lock_irqsave() to preemptible spin_trylock().
>When in hard IRQ or NMI return false right away, since
>spin_trylock() is not safe due to PI issues.
>
>Note there is no need to use local_inc for acquired variable,
>since it's a percpu variable with strict nesting scopes.
>

LGTM.

Acked-by: Davidlohr Bueso <dave at stgolabs.net>