linux-kernel - Re: [PATCH] powerpc: Drop lockdep_assert_cpus_held call from arch_update_cpu

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Date:   Thu, 5 Oct 2017 14:38:55 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Daniel Black <daniel.black@....ibm.com>
Subject: Re: [PATCH] powerpc: Drop lockdep_assert_cpus_held call from
 arch_update_cpu_topology

On Wed, 4 Oct 2017, Thiago Jung Bauermann wrote:

> It turns out that not all paths calling arch_update_cpu_topology hold
> cpu_hotplug_lock, but that's ok because those paths aren't supposed to race
> with any concurrent hotplug events.
> 
> Callers of arch_update_cpu_topology are expected to know what they are
> doing when they call the function without holding the lock, so remove the
> lockdep warning.

"Expected to know what they are doing" is not really a good approach as
it's way too simple to screw things up.

You might consider to have two functions where one does the check and the
other does not, but I leave that to the PPC maintainers.

Thanks,

	tglx