Re: [PATCH] locking: Generic ticket lock

[Mark Rutland]

Hi Peter,

On Thu, Oct 21, 2021 at 03:05:15PM +0200, Peter Zijlstra wrote:
> +static __always_inline void ticket_lock(arch_spinlock_t *lock)
> +{
> +	u32 val = atomic_fetch_add_acquire(ONE_TICKET, lock);

I wonder, should these atomics be arch_atomic_*(), in case an arch_ or raw_
lock is used in noinstr code? The plain atomic_*() forms can have explicit
inline instrumentation.

I haven't seen any issues with qspinlock so far, and that also uses the
(instrumented) atomics, so maybe that's not actually a problem, but I'm not
sure what we intend here w.r.t.  instrumentability.

Thanks,
Mark.