linux-kernel - Re: [PATCH v2 1/2] bus: arm-ccn: Fix use of smp_processor

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Date:   Wed, 04 Oct 2017 12:26:58 +0100
From:   Pawel Moll <pawel.moll@....com>
To:     Marc Zyngier <marc.zyngier@....com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
        Suzuki Poulose <Suzuki.Poulose@....com>,
        Mark Rutland <Mark.Rutland@....com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] bus: arm-ccn: Fix use of smp_processor_id() in
 preemptible context

On Tue, 2017-10-03 at 18:14 +0100, Marc Zyngier wrote:
> Booting a DEBUG_PREEMPT enabled kernel on a CCN-based system
> results in the following splat:
>
> [...]
> arm-ccn e8000000.ccn: No access to interrupts, using timer.
> BUG: using smp_processor_id() in preemptible [00000000] code:
> swapper/0/1
> caller is debug_smp_processor_id+0x1c/0x28
> CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.13.0 #6111
> Hardware name: AMD Seattle/Seattle, BIOS 17:08:23 Jun 26 2017
> Call trace:
> [<ffff000008089e78>] dump_backtrace+0x0/0x278
> [<ffff00000808a22c>] show_stack+0x24/0x30
> [<ffff000008bc3bc4>] dump_stack+0x8c/0xb0
> [<ffff00000852b534>] check_preemption_disabled+0xfc/0x100
> [<ffff00000852b554>] debug_smp_processor_id+0x1c/0x28
> [<ffff000008551bd8>] arm_ccn_probe+0x358/0x4f0
> [...]
>
> as we use smp_processor_id() in the wrong context.
>
> Turn this into a get_cpu()/put_cpu() that extends over the CPU
> hotplug
> registration, making sure that we don't race against a CPU down
> operation.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>

Acked-by: Pawel Moll <pawel.moll@....com>

I assume you'll get this merged yourself? Or do you want me to relay
the CCN one (I've got a couple of other small changes to the driver in
the queue).

Paweł
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