linux-kernel - Re: [PATCH v2] vmstat: disable vmstat_work on vmstat_cpu_down

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Message-ID: <e0b0fb6e-b00e-4256-98c7-c1c42edd6d97@lucifer.local>
Date: Mon, 6 Jan 2025 12:58:31 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Charalampos Mitrodimas <charmitro@...teo.net>
Cc: Koichiro Den <koichiro.den@...onical.com>, linux-mm@...ck.org,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2] vmstat: disable vmstat_work on vmstat_cpu_down_prep()

On Mon, Jan 06, 2025 at 12:53:36PM +0000, Charalampos Mitrodimas wrote:
> > I did a bit of printk output and it seems like this _didn't_ online CPU 0,
> > presumably the boot CPU which calls this function in the first instance?
>
> FWIW with the proposed fix I can see that all CPUs are online,
>   grep -H . /sys/devices/system/cpu/cpu*/online
>   /sys/devices/system/cpu/cpu0/online:1
>   /sys/devices/system/cpu/cpu1/online:1
>   /sys/devices/system/cpu/cpu2/online:1
>   /sys/devices/system/cpu/cpu3/online:1
>   /sys/devices/system/cpu/cpu4/online:1
>   /sys/devices/system/cpu/cpu5/online:1
>   /sys/devices/system/cpu/cpu6/online:1
>   /sys/devices/system/cpu/cpu7/online:1
>

Sorry maybe I phrased this badly, I'm not suggesting CPUs aren't coming
online, I'm saying it doesn't look like vmstat_cpu_online() will be called
for the boot CPU, which breaks the proposed fix (the delayed work for this
CPU will simply never be enabled in this case).

Naturally, the boot CPU is _already_ online at this point, which is I
imagine why this is the case.

I had wondered if the function would be invoked on the boot CPU _anyway_
but it appears not.