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

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Message-ID: <50eae15fb7ec8c6caa70811f231d69ef6f65e862.camel@physik.fu-berlin.de>
Date: Mon, 11 Aug 2025 10:28:26 +0200
From: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To: David Hildenbrand <david@...hat.com>, 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

Hi David,

thanks a lot for your input!

On Mon, 2025-08-11 at 10:20 +0200, David Hildenbrand wrote:
> 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.

Thanks, this actually explains why CONFIG_TRANSPARENT_HUGEPAGE_NEVER=y doesn't fully mitigate
the problem.

> > [  170.472743] kernel BUG at fs/ext4/inode.c:1174!
> > [  170.532313]               \|/ ____ \|/
> >                               "@'/ .. \`@"
> >                               /_| \__/ |_\
> >                                  \__U_/
> 
> Is this the
> 
> BUG_ON(to > folio_size(folio));

Yes, I just looked it up in my current local kernel tree and that's indeed the line.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913