linux-kernel - Re: [PATCH v2] NUMA: Early use of cpu_to_node() returns 0 instead of the correct node id

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Date: Wed, 24 Jan 2024 09:41:18 -0800
From: Yury Norov <yury.norov@...il.com>
To: "Lameter, Christopher" <cl@...amperecomputing.com>
Cc: Huang Shijie <shijie@...amperecomputing.com>,
	gregkh@...uxfoundation.org, patches@...erecomputing.com,
	rafael@...nel.org, paul.walmsley@...ive.com, palmer@...belt.com,
	aou@...s.berkeley.edu, kuba@...nel.org, vschneid@...hat.com,
	mingo@...nel.org, akpm@...ux-foundation.org, vbabka@...e.cz,
	rppt@...nel.org, tglx@...utronix.de, jpoimboe@...nel.org,
	ndesaulniers@...gle.com, mikelley@...rosoft.com,
	mhiramat@...nel.org, arnd@...db.de, linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com,
	will@...nel.org, mark.rutland@....com, mpe@...erman.id.au,
	linuxppc-dev@...ts.ozlabs.org, chenhuacai@...nel.org,
	jiaxun.yang@...goat.com, linux-mips@...r.kernel.org
Subject: Re: [PATCH v2] NUMA: Early use of cpu_to_node() returns 0 instead of
 the correct node id

On Wed, Jan 24, 2024 at 09:19:00AM -0800, Lameter, Christopher wrote:
> On Tue, 23 Jan 2024, Huang Shijie wrote:
> 
> > During the kernel booting, the generic cpu_to_node() is called too early in
> > arm64, powerpc and riscv when CONFIG_NUMA is enabled.
> > 
> > For arm64/powerpc/riscv, there are at least four places in the common code
> > where the generic cpu_to_node() is called before it is initialized:
> > 	   1.) early_trace_init()         in kernel/trace/trace.c
> > 	   2.) sched_init()               in kernel/sched/core.c
> > 	   3.) init_sched_fair_class()    in kernel/sched/fair.c
> > 	   4.) workqueue_init_early()     in kernel/workqueue.c
> > 
> > In order to fix the bug, the patch changes generic cpu_to_node to
> > function pointer, and export it for kernel modules.
> > Introduce smp_prepare_boot_cpu_start() to wrap the original
> > smp_prepare_boot_cpu(), and set cpu_to_node with early_cpu_to_node.
> > Introduce smp_prepare_cpus_done() to wrap the original smp_prepare_cpus(),
> > and set the cpu_to_node to formal _cpu_to_node().
> 
> Would  you please fix this cleanly without a function pointer?
> 
> What I think needs to be done is a patch series.
> 
> 1. Instrument cpu_to_node so that some warning is issued if it is used too
> early. Preloading the array with NUMA_NO_NODE would allow us to do that.

By preloading do you mean compile-time initialization?
 
> 2. Implement early_cpu_to_node on platforms that currently do not have it.
> 
> 3. A series of patches that fix each place where cpu_to_node is used too
> early.

Agree. This is the right way to go. And pretty well all of it was discussed
in v1, isn't?

Thanks,
Yury