Re: [PATCH RFC] futex: avoid false sharing between hb->chain and the bucket lock

[Peter Zijlstra]

On Tue, Jun 09, 2026 at 10:16:31PM +0200, Thomas Gleixner wrote:
> @@ -301,13 +304,12 @@ struct futex_private_hash *futex_private
>  
>  struct futex_hash_bucket *futex_hash(union futex_key *key)
>  {
> -	struct futex_private_hash *fph;
> +	struct futex_private_hash *fph = NULL;
>  	struct futex_hash_bucket *hb;
>  
>  again:
>  	scoped_guard(rcu) {
> -		hb = __futex_hash(key, NULL);
> -		fph = hb->priv;
> +		hb = __futex_hash(key, &fph);
>  
>  		if (!fph || futex_private_hash_get(fph))
>  			return hb;

Also, same bug I had in my first patch, you need to re-set fph to NULL
on the goto again :-)