linux-kernel - Re: [PATCH] kho: add support for deferred struct page init

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Message-ID: <CA+CK2bBD_aMy7k6kJH__qhYhyg=mTCQMn89+fhcCcDpJ7PJNhQ@mail.gmail.com>
Date: Tue, 30 Dec 2025 10:05:28 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Pratyush Yadav <pratyush@...nel.org>
Cc: Fadouse <fadouse@...ton.me>, Evangelos Petrongonas <epetron@...zon.de>, 
	Mike Rapoport <rppt@...nel.org>, Alexander Graf <graf@...zon.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Jason Miu <jasonmiu@...gle.com>, 
	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org, linux-mm@...ck.org, 
	nh-open-source@...zon.com
Subject: Re: [PATCH] kho: add support for deferred struct page init

On Mon, Dec 29, 2025 at 4:09 PM Pratyush Yadav <pratyush@...nel.org> wrote:
>
> On Wed, Dec 24 2025, Fadouse wrote:
>
> > Hi Evangelos, Mike, Pasha, Pratyush,
> >
> > I independently hit a crash in the LUO/memfd restore path with
> > CONFIG_DEFERRED_STRUCT_PAGE_INIT=y, on a local build based on dd9b004b7ff3
> > (x86_64 QEMU, 6.19.0-rc1 timeframe).
>
> How? config KEXEC_HANDOVER depends on !DEFERRED_STRUCT_PAGE_INIT. So you
> shouldn't even be able to enable KHO or LUO with
> CONFIG_DEFERRED_STRUCT_PAGE_INIT=y. Are you sure it is enabled?

I think, Fadouse reported a bug with this patch applied, not an upstream bug.

Pasha

>
> >
> > In my reproducer, stage1 preserves a memfd via LUO and kexecs into stage2;
> > stage2 calls LIVEUPDATE_SESSION_FINISH without retrieving files. I observed
> > a reliable crash in adjust_managed_page_count() from kho_restore_page().
> >
> > Minimal excerpt:
> >
> > stage2: start
> > stage2: retrieved session fd=4
> > BUG: unable to handle page fault for address: 0000000000001410
> > RIP: adjust_managed_page_count+0x29/0x40
> > Call Trace:
> >   kho_restore_page+0x18a/0x1c0
> >   kho_restore_folio+0xe/0x60
> >   memfd_luo_finish+0xe6/0x160
> >   luo_file_finish+0x188/0x240
> >   luo_session_finish+0x2c/0x80
> >   luo_session_ioctl+0xf5/0x170
> >   __x64_sys_ioctl+0x91/0xe0
> >
> > Applying the patch in <20251216084913.86342-1-epetron@...zon.de> makes the
> > issue no longer reproduce for me.
> >
> > I can share full logs and the small two-stage initramfs reproducer if needed.
> >
> > Thanks,
> > YanXin Li
> >
> > Tested-by: YanXin Li <fadouse@...ton.me>
> >
> [...]
>
> --
> Regards,
> Pratyush Yadav