linux-kernel - Re: [PATCH v3] ARM64: Dynamically allocate cpumasks and increase supported CPUs to 512

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Message-ID: <e3952dc0-ec28-e7c7-e858-c47f146c93de@linux.com>
Date: Fri, 8 Mar 2024 09:08:59 -0800 (PST)
From: "Christoph Lameter (Ampere)" <cl@...ux.com>
To: Marek Szyprowski <m.szyprowski@...sung.com>
cc: Catalin Marinas <catalin.marinas@....com>, 
    Mark Rutland <mark.rutland@....com>, 
    "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>, 
    "Rafael J. Wysocki" <rafael@...nel.org>, Viresh Kumar <vireshk@...nel.org>, 
    Will Deacon <will@...nel.org>, Jonathan.Cameron@...wei.com, 
    Matteo.Carlini@....com, Valentin.Schneider@....com, 
    akpm@...ux-foundation.org, anshuman.khandual@....com, 
    Eric Mackay <eric.mackay@...cle.com>, dave.kleikamp@...cle.com, 
    linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
    linux-mm@...ck.org, linux@...linux.org.uk, robin.murphy@....com, 
    vanshikonda@...amperecomputing.com, yang@...amperecomputing.com, 
    Nishanth Menon <nm@...com>, Stephen Boyd <sboyd@...nel.org>
Subject: Re: [PATCH v3] ARM64: Dynamically allocate cpumasks and increase
 supported CPUs to 512

On Fri, 8 Mar 2024, Marek Szyprowski wrote:

>>>
>>> It looks that cpufreq-dt and/or opp drivers needs some adjustments
>>> related with this change.
>> That's strange. Is this with defconfig? I wonder whether NR_CPUS being
>> larger caused the issue with this specific code. Otherwise
>> CPUMASK_OFFSTACK may not work that well on arm64.

cpumask handling must use the accessor functions provided in 
include/linux/cpumask.h for declaring and accessing cpumasks. It is likely 
related to the driver opencoding one of the accessors.

I.e. you must use alloc_cpumask_var() and not allocate yourself on the 
stack.