From: Thomas Gleixner <tglx@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Breno Leitao" <leitao@debian.org>,
"Ingo Molnar" <mingo@redhat.com>,
"Darren Hart" <dvhart@infradead.org>,
"Davidlohr Bueso" <dave@stgolabs.net>,
"André Almeida" <andrealmeid@igalia.com>,
linux-kernel@vger.kernel.org, puranjay@kernel.org,
rmikey@meta.com, stuclar@meta.com, namhyung@kernel.org,
kernel-team@meta.com
Subject: Re: [PATCH RFC] futex: avoid false sharing between hb->chain and the bucket lock
Date: Tue, 09 Jun 2026 22:32:24 +0200 [thread overview]
Message-ID: <87jys7315z.ffs@fw13> (raw)
In-Reply-To: <20260609202527.GC187714@noisy.programming.kicks-ass.net>
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 :)
prev parent reply other threads:[~2026-06-09 20:32 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-05 16:53 [PATCH RFC] futex: avoid false sharing between hb->chain and the bucket lock Breno Leitao
2026-06-09 10:46 ` Peter Zijlstra
2026-06-09 15:28 ` Breno Leitao
2026-06-09 20:11 ` Peter Zijlstra
2026-06-09 20:18 ` Peter Zijlstra
2026-06-09 20:16 ` Thomas Gleixner
2026-06-09 20:23 ` Peter Zijlstra
2026-06-09 20:25 ` Peter Zijlstra
2026-06-09 20:32 ` Thomas Gleixner [this message]
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