From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@kernel.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, 9 Jun 2026 22:25:27 +0200 [thread overview]
Message-ID: <20260609202527.GC187714@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <87mrx331wg.ffs@fw13>
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 :-)
next prev parent reply other threads:[~2026-06-09 20:25 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-05 16:53 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
2026-06-10 11:22 ` Thomas Gleixner
2026-06-10 11:25 ` Peter Zijlstra
2026-06-10 13:55 ` Peter Zijlstra
2026-06-12 7:11 ` [tip: locking/core] futex: Optimize futex hash bucket access patterns tip-bot2 for Peter Zijlstra
2026-06-12 8:13 ` Breno Leitao
2026-06-10 13:56 ` [PATCH RFC] futex: avoid false sharing between hb->chain and the bucket lock Breno Leitao
2026-06-23 10:30 ` Breno Leitao
2026-06-09 20:16 ` Thomas Gleixner
2026-06-09 20:23 ` Peter Zijlstra
2026-06-09 20:25 ` Peter Zijlstra [this message]
2026-06-09 20:32 ` Thomas Gleixner
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