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Date:   Mon, 4 Sep 2023 23:23:24 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Elliot Berman <quic_eberman@quicinc.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Pavel Machek <pavel@ucw.cz>,
        Thomas Gleixner <tglx@linutronix.de>, kernel@quicinc.com,
        linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-pm@vger.kernel.org,
        Prakash Viswalingam <quic_prakashv@quicinc.com>
Subject: Re: [PATCH v2] freezer,sched: Use saved_state to reduce some
 spurious wakeups
Message-ID: <20230904212324.GA2568@noisy.programming.kicks-ass.net>
References: <20230830-avoid-spurious-freezer-wakeups-v2-1-8877245cdbdc@quicinc.com>
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On Wed, Aug 30, 2023 at 10:42:39AM -0700, Elliot Berman wrote:

> Avoid the spurious wakeups by saving the state of TASK_FREEZABLE tasks.
> If the task was running before entering TASK_FROZEN state
> (__refrigerator()) or if the task received a wake up for the saved
> state, then the task is woken on thaw. saved_state from PREEMPT_RT locks
> can be re-used because freezer would not stomp on the rtlock wait flow:
> TASK_RTLOCK_WAIT isn't considered freezable.

You don't actually assert that anywhere I think, so the moment someone
makes that happen you crash and burn.

Also:

> -#ifdef CONFIG_PREEMPT_RT
> +#if IS_ENABLED(CONFIG_PREEMPT_RT) || IS_ENABLED(CONFIG_FREEZER)

That makes wakeup more horrible for everyone :/