Re: [RFC PATCH] srcu: Use try-lock lockdep annotation for NMI-safe access.

[Peter Zijlstra]

On Wed, Sep 27, 2023 at 11:06:09PM -0700, Boqun Feng wrote:

> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index e85b5ad3e206..1af8d44e5eb4 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -5727,8 +5727,9 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
>                 return;
> 
>         if (unlikely(!lockdep_enabled())) {
> +               /* Only do NMI context checking if it's a check lock */
>                 /* XXX allow trylock from NMI ?!? */
> -               if (lockdep_nmi() && !trylock) {
> +               if (check && lockdep_nmi() && !trylock) {
>                         struct held_lock hlock;
> 
>                         hlock.acquire_ip = ip;
> 
> Peter, thoughts?
> 

I think I prefer the trylock one. Fundamentally trylock conveys the 'we
wont block' thing. Making 'lock' sometimes work for NMI is just
confusing.