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Subject: Re: [PATCH v2 1/2] bus: arm-ccn: Fix use of smp_processor_id() in
 preemptible context
To: Pawel Moll <pawel.moll@arm.com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
        Suzuki Poulose <Suzuki.Poulose@arm.com>,
        Mark Rutland <Mark.Rutland@arm.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20171003171413.18592-1-marc.zyngier@arm.com>
 <20171003171413.18592-2-marc.zyngier@arm.com>
 <1507116418.3164.97.camel@arm.com>
From: Marc Zyngier <marc.zyngier@arm.com>
Organization: ARM Ltd
Message-ID: <a6bab179-0284-c394-3042-3147a01bde6d@arm.com>
Date: Wed, 4 Oct 2017 13:32:11 +0100
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On 04/10/17 12:26, Pawel Moll wrote:
> 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@arm.com>
> 
> Acked-by: Pawel Moll <pawel.moll@arm.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).

I'd rather you take care of it if you already have a queue of patches.
Otherwise, I'll bundle the two patches and ask the armsoc folks to do
something with them.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...