Re: git: 80cf427b8dc1 - main - proc: shave a lock trip on exit if possible

On Wed, Mar 29, 2023 at 09:19:09AM +0000, Mateusz Guzik wrote:
> The branch main has been updated by mjg:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=80cf427b8dc18bc5c26fed6d07bc5c5eda4545b0
> 
> commit 80cf427b8dc18bc5c26fed6d07bc5c5eda4545b0
> Author:     Mateusz Guzik <mjg@FreeBSD.org>
> AuthorDate: 2023-03-29 08:45:46 +0000
> Commit:     Mateusz Guzik <mjg@FreeBSD.org>
> CommitDate: 2023-03-29 09:19:03 +0000
> 
>     proc: shave a lock trip on exit if possible
>     
>     ... which happens to be vast majority of the time
> ---
>  sys/kern/kern_exit.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
> index 3f64343aea0e..a92d5cc0f642 100644
> --- a/sys/kern/kern_exit.c
> +++ b/sys/kern/kern_exit.c
> @@ -477,9 +477,11 @@ exit1(struct thread *td, int rval, int signo)
>  	sx_xunlock(&allproc_lock);
>  
>  	sx_xlock(&proctree_lock);
> -	PROC_LOCK(p);
> -	p->p_flag &= ~(P_TRACED | P_PPWAIT | P_PPTRACE);
> -	PROC_UNLOCK(p);
> +	if ((p->p_flag & (P_TRACED | P_PPWAIT | P_PPTRACE)) != 0) {
> +		PROC_LOCK(p);
> +		p->p_flag &= ~(P_TRACED | P_PPWAIT | P_PPTRACE);
> +		PROC_UNLOCK(p);
> +	}

just out of curiosuty, is this can be replaced by a single
atomic_clear_rel ?

>  
>  	/*
>  	 * killjobc() might drop and re-acquire proctree_lock to