linux-kernel - Re: [RFC 1/2] refcount: introduce generic lockptr funcs

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Date:   Fri, 3 Nov 2023 19:54:14 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexander Aring <aahringo@...hat.com>
Cc:     will@...nel.org, gfs2@...ts.linux.dev, boqun.feng@...il.com,
        mark.rutland@....com, linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/2] refcount: introduce generic lockptr funcs

On Fri, Nov 03, 2023 at 12:16:34PM -0400, Alexander Aring wrote:

> diff --git a/lib/refcount.c b/lib/refcount.c
> index a207a8f22b3c..e28678f0f473 100644
> --- a/lib/refcount.c
> +++ b/lib/refcount.c
> @@ -94,6 +94,34 @@ bool refcount_dec_not_one(refcount_t *r)
>  }
>  EXPORT_SYMBOL(refcount_dec_not_one);
>  
> +bool refcount_dec_and_lockptr(refcount_t *r, void (*lock)(void *lockptr),
> +			      void (*unlock)(void *lockptr),  void *lockptr)
> +{
> +	if (refcount_dec_not_one(r))
> +		return false;
> +
> +	lock(lockptr);
> +	if (!refcount_dec_and_test(r)) {
> +		unlock(lockptr);
> +		return false;
> +	}
> +
> +	return true;
> +}
> +EXPORT_SYMBOL(refcount_dec_and_lockptr);

This is terrible, you're forcing indirect calls on everything.