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

[Thomas Gleixner]

On Tue, Jun 09 2026 at 22:25, Peter Zijlstra wrote:
> 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 :-)

Figured that out by now :)