Re: [PATCH bpf-next v8 3/6] locking/local_lock: Introduce localtry_lock_t

[Vlastimil Babka <vbabka@suse.cz>]

On 2/13/25 04:35, Alexei Starovoitov wrote:
> From: Sebastian Andrzej Siewior <bigeasy@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.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>

I'm not the maintainer of this area, but with the fixes/addition I proposed,
and having use for this lock variant myself, I think it's fair to add, fwiw:

Acked-by: Vlastimil Babka <vbabka@suse.cz>

Thanks.