linux-kernel - Re: [PATCH] riscv: BUG_ON() for no cpu nodes in setup

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Message-ID: <20230630-tightrope-clatter-6eed9875a76f@wendy>
Date:   Fri, 30 Jun 2023 07:33:55 +0100
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     Song Shuai <suagrfillet@...il.com>
CC:     <paul.walmsley@...ive.com>, <palmer@...belt.com>,
        <aou@...s.berkeley.edu>, <ajones@...tanamicro.com>,
        <sunilvl@...tanamicro.com>, <heiko.stuebner@...ll.eu>,
        <apatel@...tanamicro.com>, <evan@...osinc.com>,
        <greentime.hu@...ive.com>, <leyfoon.tan@...rfivetech.com>,
        <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] riscv: BUG_ON() for no cpu nodes in setup_smp

Hey,

On Fri, Jun 30, 2023 at 11:02:18AM +0800, Song Shuai wrote:
> 在 2023/6/29 20:33, Conor Dooley 写道:
> > On Thu, Jun 29, 2023 at 06:58:39PM +0800, Song Shuai wrote:
> > > When booting with ACPI tables, the tiny devictree created by
> > > EFI Stub doesn't provide cpu nodes.
> > 
> 
> "When only the ACPI tables are passed to kernel, the tiny..."
> That seems more accurate. We can use "acpi=" kernel
> parameter to manually enable/disable ACPI.
> 
> > What are the conditions that are required to reproduce this issue?
> > When booting with ACPI, why is acpi_disabled true?
> > In my naivety, that seems like a bigger problem to address. >
> 
> Actually, I appended the "acpi=off" to kernel cmdline for testing the "off"
> option. That would set acpi_disabled as true.

Yeah, I figured it was intentionally misconfiguration of your kernel,
given that you've tested other niche conditions and reported bugs, just
was not clear from your commit message whether this was a real bugTM
that should be fixed, or some sort of "you booted a kernel that can't be
used on this system".

> > > That's unclear, so bug for no cpu nodes before
> > > of_parse_and_init_cpus().
> > 
> > What is unclear? That the reason for the BUG() was that there were no
> > cpu nodes, since it could also be that there were CPU nodes but they
> > were disabled etc?
> 
> The BUG() in of_parse_and_init_cpus() indicates there was no boot cpu found
> in the devicetree , not there were no cpu nodes in the devices.
> That's the "unclear" I mean.

Yup, please put that in the commit message so that people don't have to
figure out your intent ;)

> > Or, better yet, move the whole thing into of_parse_and_init_cpus() in
> > the first place? You could drop most of the comment in the process,
> > since I think the details of how you hit this problem would likely not
> > be helpful to anyone that hit it under different conditions.

> ok, I'll apply these comments if you're ok with my replies.

Yup, thanks!

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