linux-kernel - Re: [PATCH] sparc64: fix hugetlb for sun4u

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Message-ID: <96992842-f576-4e19-afcb-7455452fe506@redhat.com>
Date: Mon, 11 Aug 2025 10:20:10 +0200
From: David Hildenbrand <david@...hat.com>
To: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
 Anthony Yznaga <anthony.yznaga@...cle.com>, sparclinux@...r.kernel.org,
 davem@...emloft.net, andreas@...sler.com
Cc: linux-kernel@...r.kernel.org, agordeev@...ux.ibm.com, will@...nel.org,
 ryan.roberts@....com, osalvador@...e.de
Subject: Re: [PATCH] sparc64: fix hugetlb for sun4u

On 09.08.25 08:23, John Paul Adrian Glaubitz wrote:
> Hi Anthony,
> 
> On Sat, 2025-08-09 at 00:37 +0200, John Paul Adrian Glaubitz wrote:
>>> Maybe try enabling CONFIG_DEBUG_VM_IRQSOFF, CONFIG_DEBUG_VM, and perhaps
>>> CONFIG_DEBUG_VM_PGFLAGS. That might help detect a problem closer to the
>>> source. You can also try adding transparent_hugepage=never to the kernel
>>> boot line to see if compiling in THP support but not using it is okay.
>>
>> OK, I will try that. But not today anymore. It's half past midnight now here in Germany
>> and I was debugging this issue almost all day long. I'm glad to have finally been able
>> to track this down to THP support being enabled.
>>
>> Maybe you can try whether you can reproduce this in QEMU as well.
> 
> OK, first data point: Setting CONFIG_TRANSPARENT_HUGEPAGE_NEVER=y causes the backtrace during
> boot to disappear with CONFIG_TRANSPARENT_HUGEPAGE=y. However, it still disappears later when
> running "apt update && apt -y upgrade" again:

Just to give some context: (m)THPs in file systems will get used 
independently of CONFIG_TRANSPARENT_HUGEPAGE_NEVER=y.

So CONFIG_TRANSPARENT_HUGEPAGE_NEVER=y primarily only controls usage of 
(m)THPs for anonymous memory, but not in the pagecache.


> 
> [  170.472743] kernel BUG at fs/ext4/inode.c:1174!
> [  170.532313]               \|/ ____ \|/
>                               "@'/ .. \`@"
>                               /_| \__/ |_\
>                                  \__U_/

Is this the

BUG_ON(to > folio_size(folio));

?

-- 
Cheers,

David / dhildenb