linux-kernel - Re: [v5 PATCH 5/8] RISC-V: Compare cpuid with NR

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Date:   Thu, 14 Feb 2019 15:33:22 -0800
From:   Atish Patra <atish.patra@....com>
To:     Christopher Lameter <cl@...ux.com>
Cc:     "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Jason Cooper <jason@...edaemon.net>,
        Alan Kao <alankao@...estech.com>,
        Dmitriy Cherkasov <dmitriy@...-tech.org>,
        Anup Patel <anup@...infault.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Johan Hovold <johan@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Palmer Dabbelt <palmer@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Andreas Schwab <schwab@...e.de>,
        Marc Zyngier <marc.zyngier@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Guenter Roeck <linux@...ck-us.net>
Subject: Re: [v5 PATCH 5/8] RISC-V: Compare cpuid with NR_CPUS before mapping.

On 2/14/19 9:59 AM, Christopher Lameter wrote:
> On Wed, 13 Feb 2019, Atish Patra wrote:
> 
>> --- a/arch/riscv/kernel/smpboot.c
>> +++ b/arch/riscv/kernel/smpboot.c
>> @@ -66,6 +66,11 @@ void __init setup_smp(void)
>>   			found_boot_cpu = 1;
>>   			continue;
>>   		}
>> +		if (cpuid >= NR_CPUS) {
> 
> Use nr_cpu_ids instead? Its initialized to NR_CPUS but can be restricted
> if we can determine on boot how many processor we truly have.
> 
nr_cpu_ids can be modified by nr_cpus in boot command line. If nr_cpus 
is set to a value less than number of cpus described in the DT, kernel 
may not boot depending on the boot hartid. This happens because we break 
out of the while loop and BUG_ON(!found_boot_cpu).

As the required fix will be different from the current fix, I would like 
to do this in a follow up patch if that's ok.

Btw, thanks for bringing this up.

Regards,
Atish