linux-kernel - Re: [PATCH] cpu/hotplug: Fix rollback during error-out in takedown

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Message-ID: <alpine.DEB.2.21.1809051512450.1416@nanos.tec.linutronix.de>
Date:   Wed, 5 Sep 2018 15:14:01 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Mukesh Ojha <mojha@...eaurora.org>
cc:     Neeraj Upadhyay <neeraju@...eaurora.org>, josh@...htriplett.org,
        peterz@...radead.org, mingo@...nel.org, jiangshanlai@...il.com,
        dzickus@...hat.com, brendan.jackman@....com, malat@...ian.org,
        linux-kernel@...r.kernel.org, sramana@...eaurora.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] cpu/hotplug: Fix rollback during error-out in
 takedown_cpu()

On Wed, 5 Sep 2018, Mukesh Ojha wrote:
> On 9/5/2018 5:03 PM, Thomas Gleixner wrote:
> > > +		st->rollback = true;
> > > +		st->target = prev_state;
> > > +		st->bringup = !st->bringup;
> > No, this is just papering over the actual problem.
> > 
> > The state inconsistency happens in take_cpu_down() when it returns with a
> > failure from __cpu_disable() because that returns with state = TEARDOWN_CPU
> > and st->state is then incremented in undo_cpu_down().
> > 
> > That's the real issue and we need to analyze the whole cpu_down rollback
> > logic first.
> 
> Could this be done like below ?

IOW, more papering over the real root cause.

> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index aa7fe85..47bce90 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -802,17 +802,18 @@ static int take_cpu_down(void *_param)
>         int err, cpu = smp_processor_id();
>         int ret;

  ^^^^^^^

Please fix your mailer or your editor. That patch is whitespace damaged.

Thanks,

	tglx