From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: John Stultz <jstultz@google.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Christian Loehle <christian.loehle@arm.com>,
Qais Yousef <qyousef@google.com>,
LKML <linux-kernel@vger.kernel.org>,
Hongyan Xia <hongyan.xia2@arm.com>,
Ingo Molnar <mingo@kernel.org>, Wei Wang <wvw@google.com>,
Patrick Bellasi <patrick.bellasi@arm.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>
Subject: Re: Uclamp races due to non-atomic static_branch_likely updates
Date: Wed, 21 Oct 2026 09:59:55 -0400 [thread overview]
Message-ID: <20261021095955.0d06a754@gandalf.local.home> (raw)
In-Reply-To: <20261021133430.GP2823843@noisy.programming.kicks-ass.net>
On Wed, 21 Oct 2026 15:34:30 +0200
Peter Zijlstra <peterz@infradead.org> wrote:
> That simply doesn't work.
>
> Even *IF* memory stores would propagate instantly (they don't) you can
> still have the boolean swap while in the middle of this state.
>
> ---
>
> B = true;
>
> CPU0 CPU1
>
> enqueue
> if (B)
> something++;
>
> B = false;
>
> dequeue
> if (B)
> something--;
>
>
> ---
>
> Will still be left with something unbalanced, even if everything is
> super duper magically atomic.
Fair point.
-- Steve
next prev parent reply other threads:[~2026-10-21 14:00 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-20 18:53 John Stultz
2026-10-20 19:29 ` Steven Rostedt
2026-10-21 11:38 ` Peter Zijlstra
2026-10-21 13:20 ` Qais Yousef
2026-10-21 13:29 ` Peter Zijlstra
2026-10-21 14:02 ` Qais Yousef
2026-10-21 13:21 ` Steven Rostedt
2026-10-21 13:34 ` Peter Zijlstra
2026-10-21 13:59 ` Steven Rostedt [this message]
2026-10-21 17:56 ` John Stultz
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