linux-kernel - Re: Issue related cpuhotplug failure path on 4.9.x version

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Date:   Mon, 23 Jul 2018 14:49:27 +0530
From:   Mukesh Ojha <mojha@...eaurora.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>, gkohli@...eaurora.org,
        Maria Yu <aiquny@...eaurora.org>,
        Prasad Sodagudi <psodagud@...eaurora.org>,
        neeraju@...eaurora.org, stable@...r.kernel.org
Cc:     lkml <linux-kernel@...r.kernel.org>
Subject: Re: Issue related cpuhotplug failure path on 4.9.x version

Adding stable and lkml.

Sorry for spam others.

-Mukesh

On 7/23/2018 1:57 PM, Mukesh Ojha wrote:
>
> Hi All,
>
> I wanted to discuss about one of the corner case exists in 4.9 kernel 
> (4.9.x) where
> If hotplug of one of the CPU fails due to failure in one of the callback,
> which is to be called after "notify:online"(as notify_online will 
> create sysfs nodes
> for the hotplug cpu) .
>
> So, while cleaning up notify_dead() does not get called as step 
> <https://elixir.bootlin.com/linux/v4.9/ident/step>->skip_onerr set to
> true for "notify:prepare"and due to that sysfs nodes of that cpu does 
> not get
> cleaned up which can cause issue in next hotplug attempt of that cpu.
>
>                                                    Fails
> cpuhp_up_callbacks 
> <https://elixir.bootlin.com/linux/v4.9/ident/cpuhp_up_callbacks> => 
> cpuhp_invoke_callback 
> <https://elixir.bootlin.com/linux/v4.9/ident/cpuhp_invoke_callback> => 
> undo_cpu_up <https://elixir.bootlin.com/linux/v4.9/ident/undo_cpu_up>
>
> .name = "notify:prepare",
> .teardown.single = notify_dead 
> <https://elixir.bootlin.com/linux/v4.9/ident/notify_dead>,
> .skip_onerr = true,
>
> I think the possible solution here could be to remove the
> -            .skip_onerr = true,
>
> for "notify:prepare"so that CPU_DEAD notification get send.
>
> Please, feel free to suggest if it has any side-effect as i don't feel 
> any.
>
> Ref:
>
> https://elixir.bootlin.com/linux/v4.9/source/kernel/cpu.c#L458
>
> Cheers,
> Mukesh
>
>
>
>
>
>


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