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Date: Tue, 20 May 2025 16:20:15 -0700
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Subject: Re: [PATCH 1/3] drivers/edac: Add L1 and L2 error detection for A72
To: Borislav Petkov <bp@alien8.de>
Cc: Tony Luck <tony.luck@intel.com>, Rob Herring <robh@kernel.org>,
 Krzysztof Kozlowski <krzk+dt@kernel.org>, Conor Dooley
 <conor+dt@kernel.org>, James Morse <james.morse@arm.com>,
 Mauro Carvalho Chehab <mchehab@kernel.org>, Robert Richter
 <rric@kernel.org>, linux-edac@vger.kernel.org, linux-kernel@vger.kernel.org,
 Tyler Hicks <code@tyhicks.com>, Marc Zyngier <maz@kernel.org>,
 Sascha Hauer <s.hauer@pengutronix.de>,
 Lorenzo Pieralisi <lpieralisi@kernel.org>, devicetree@vger.kernel.org
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From: Vijay Balakrishna <vijayb@linux.microsoft.com>
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On 5/20/2025 1:04 PM, Borislav Petkov wrote:
> On Tue, May 20, 2025 at 12:54:32PM -0700, Vijay Balakrishna wrote:
>> On 5/20/2025 9:09 AM, Vijay Balakrishna wrote:
>>> On 5/19/2025 1:51 AM, Borislav Petkov wrote:
>>>> I'd venture a guess you need to protect here against CPU hotplug...
>>>>
>>>>> +    for_each_cpu_and(cpu, cpu_online_mask, &compat_mask) {
>>>>> +        smp_call_function_single(cpu, read_errors, &merrsr, true);
>>>>> +        report_errors(edac_ctl, cpu, &merrsr);
>>>>> +    }
>>>>> +}
>>>>> +
>>>
>>> Hi Boris,
>>>
>>> I appreciate you highlighting the CPU hotplug issue. Upon further review
>>> of surrounding code, I realized we must ensure that the data passed to
>>> read_errors() is per-CPU.
>>
>> Actually, per-CPU data not needed as we are passing true -- wait until
>> function has completed on other CPUs.
> 
> What happens if @cpu above gets offlined right before you do
> smp_call_function_single() ?

We can see inconsistent behavior or kernel crash/hang. You are correct, 
we need to protect against CPU hotplug. I will add 
cpus_read_lock()/cpus_read_unlock().

Thanks,
Vijay