linux-kernel - Re: [RFC][PATCH 5/7] sched,livepatch: Use wake_up_if

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Date:   Wed, 22 Sep 2021 15:05:03 +0200 (CEST)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     gor@...ux.ibm.com, jpoimboe@...hat.com, jikos@...nel.org,
        pmladek@...e.com, mingo@...nel.org, linux-kernel@...r.kernel.org,
        joe.lawrence@...hat.com, fweisbec@...il.com, tglx@...utronix.de,
        hca@...ux.ibm.com, svens@...ux.ibm.com, sumanthk@...ux.ibm.com,
        live-patching@...r.kernel.org, paulmck@...nel.org
Subject: Re: [RFC][PATCH 5/7] sched,livepatch: Use wake_up_if_idle()

> @@ -405,8 +405,10 @@ void klp_try_complete_transition(void)
>  	for_each_possible_cpu(cpu) {
>  		task = idle_task(cpu);
>  		if (cpu_online(cpu)) {
> -			if (!klp_try_switch_task(task))
> -				complete = false;
> +			int ret = klp_try_switch_task(task);
> +			if (ret == -EBUSY)
> +				wake_up_if_idle(cpu);
> +			complete = !ret;

This is broken. You can basically change "complete" only to false (when it 
applies). This could leave some tasks in the old patching state.

Anyway, I like the patch set a lot. It moves our infrastructure to a 
proper (I hope so) API and it removes few quirks we have along the way. 
I'll play with it some more.

Thanks

Miroslav