linux-kernel - Re: [PATCH v3 6/6] freezer,sched: Rewrite core freezer logic

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Date:   Mon, 26 Sep 2022 14:55:45 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christian Borntraeger <borntraeger@...ux.ibm.com>
Cc:     bigeasy@...utronix.de, dietmar.eggemann@....com,
        ebiederm@...ssion.com, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, mgorman@...e.de, mingo@...nel.org,
        oleg@...hat.com, rjw@...ysocki.net, rostedt@...dmis.org,
        tj@...nel.org, vincent.guittot@...aro.org, will@...nel.org,
        Marc Hartmayer <mhartmay@...ux.ibm.com>,
        Amit Shah <amit@...nel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH v3 6/6] freezer,sched: Rewrite core freezer logic

On Mon, Sep 26, 2022 at 02:32:24PM +0200, Christian Borntraeger wrote:
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index 9fa3c76a267f..e93df4f735fe 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -790,7 +790,7 @@ static int wait_port_writable(struct port *port, bool nonblock)
>                 if (nonblock)
>                         return -EAGAIN;
> -               ret = wait_event_freezable(port->waitqueue,
> +               ret = wait_event_interruptible(port->waitqueue,
>                                            !will_write_block(port));
>                 if (ret < 0)
>                         return ret;
> 
> Does fix the problem.

It's almost as if someone does try_to_wake_up(.state = TASK_FREEZABLE)
-- which would be quite insane.

Could you please test with something like the below on? I can boot that
with KVM, but obviously I didn't suffer any weirdness to begin with :/

---
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4e6a6417211f..ef9ccfc3a8c0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4051,6 +4051,8 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
 	unsigned long flags;
 	int cpu, success = 0;
 
+	WARN_ON_ONCE(state & TASK_FREEZABLE);
+
 	preempt_disable();
 	if (p == current) {
 		/*