linux-kernel - Re: [PATCH] x86/microcode: Fix the microcode load on CPU hotplug for real

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Message-ID: <CAE=gft6=TPF9xYmVbzR2WQJ8LDQjPm_cZ17cyHaPrh-K9UCgHA@mail.gmail.com>
Date:   Wed, 26 Jun 2019 10:20:12 -0700
From:   Evan Green <evgreen@...omium.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86/microcode: Fix the microcode load on CPU hotplug for real

On Tue, Jun 18, 2019 at 1:31 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> A recent change moved the microcode loader hotplug callback into the early
> startup phase, which is running with interrupts disabled. It missed that
> the callbacks invoke sysfs functions which might sleep causing nice 'might
> sleep' splats with proper debugging enabled.
>
> Split the callbacks and only load the microcode in the early startup phase
> and move the sysfs handling back into the later threaded and preemptible
> bringup phase where it was before.
>
> Fixes: 78f4e932f776 ("x86/microcode, cpuhotplug: Add a microcode loader CPU hotplug callback")
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

I ran into the bug fixed by this. For 4.19:
Tested-by: Evan Green <evgreen@...omium.org>