linux-kernel - Re: [PATCH] x86/microcode, cpuhotplug: move microcode hotplug callback after cpu teardown

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Date:   Wed, 3 Jul 2019 11:17:04 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Song liwei <liwei.song@...driver.com>
cc:     linux-kernel@...r.kernel.org,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Will Deacon <will@...nel.org>, Borislav Petkov <bp@...e.de>,
        Kulkarni <Ganapatrao.Kulkarni@...ium.com>,
        Guo Ren <ren_guo@...ky.com>, Joseph Lo <josephl@...dia.com>,
        Hoan Tran <Hoan@...amperecomputing.com>,
        Anju T Sudhakar <anju@...ux.vnet.ibm.com>,
        Rafael J <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH] x86/microcode, cpuhotplug: move microcode hotplug callback
 after cpu teardown

On Wed, 3 Jul 2019, Song liwei wrote:

> After CPUHP_TEARDOWN_CPU callback was invoked, the context will become
> atomic and IRQ disabled, while mc_cpu_down_prep will called
> kernfs_find_and_get_ns which will try to acquire mutext lock which may
> sleep.
> 
> Adjust CPUHP_AP_MICROCODE_LOADER callback function run before
> CPUHP_TEARDOWN_CPU to fix this bug.

That's just wrong and reintroduces the bug which was fixed with that commit
as perf will access a non existing MSR which is brought in by the micro
code update.

Aside of that the mutex issue _is_ fixed in rc7 already:

 5423f5ce5ca4 ("x86/microcode: Fix the microcode load on CPU hotplug for real")

Thanks,

	tglx