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

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Message-ID: <alpine.DEB.2.21.1809051514070.1416@nanos.tec.linutronix.de>
Date:   Wed, 5 Sep 2018 15:17:06 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Neeraj Upadhyay <neeraju@...eaurora.org>
cc:     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, Neeraj Upadhyay wrote:
> On 09/05/2018 05:53 PM, Thomas Gleixner wrote:
> >
> > And looking closer this is a general issue. Just that the TEARDOWN state
> > makes it simple to observe. It's universaly broken, when the first teardown
> > callback fails because, st->state is only decremented _AFTER_ the callback
> > returns success, but undo_cpu_down() increments unconditionally.
> >
>
> As per my understanding, there are 2 problems here; one is fixed with your
> patch, and other is cpuhp_reset_state() is used during rollback from non-AP to
> AP state, which seem to result in 2 increments of st->state (one increment
> done by cpuhp_reset_state() and another by cpu_thread_fun()) .

And how did your hack fix that up magically? I'll have a look later today.

Thanks,

	tglx