linux-kernel - Re: [PATCH 1/2] mm/khugepaged: do synchronous writeback for MADV

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <05CAD17E-CF58-4825-A36C-EE428390AD23@nvidia.com>
Date: Mon, 10 Nov 2025 16:56:37 -0500
From: Zi Yan <ziy@...dia.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: "Garg, Shivank" <shivankg@....com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...hat.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
 Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
 Barry Song <baohua@...nel.org>, Lance Yang <lance.yang@...ux.dev>,
 Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 "Zach O'Keefe" <zokeefe@...gle.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 Branden Moore <Branden.Moore@....com>
Subject: Re: [PATCH 1/2] mm/khugepaged: do synchronous writeback for
 MADV_COLLAPSE

On 10 Nov 2025, at 16:16, Lorenzo Stoakes wrote:

> OK ignore the past mail, I have managed to repro this locally and have a
> fix.
>
> Turns out the swap code is doing something quite insane... I will send
> fix-patches to the series shortly.
>
> Meanwhile I attach fix-patch! :)
>
> Cheers, Lorenzo
>
> ----8<----
> From c705fd85a806f53017df31e6b072c4bfa839e3a2 Mon Sep 17 00:00:00 2001
> From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Date: Mon, 10 Nov 2025 21:11:52 +0000
> Subject: [PATCH] fix
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> ---
>  include/linux/leafops.h |  4 ++--
>  mm/swapfile.c           | 12 ++++++++++--
>  2 files changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/leafops.h b/include/linux/leafops.h
> index a464a7e08c76..c4cd36760ea0 100644
> --- a/include/linux/leafops.h
> +++ b/include/linux/leafops.h
> @@ -56,7 +56,7 @@ static inline softleaf_t softleaf_from_pte(pte_t pte)
>  {
>  	softleaf_t arch_entry;
>
> -	if (pte_present(pte))
> +	if (pte_present(pte) || pte_none(pte))
>  		return softleaf_mk_none();
>
>  	pte = pte_swp_clear_flags(pte);
> @@ -95,7 +95,7 @@ static inline softleaf_t softleaf_from_pmd(pmd_t pmd)
>  {
>  	softleaf_t arch_entry;
>
> -	if (pmd_present(pmd))
> +	if (pmd_present(pmd) || pmd_none(pmd))
>  		return softleaf_mk_none();
>
>  	if (pmd_swp_soft_dirty(pmd))
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index fd23d9f7ae10..f0dcf261f652 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -3202,9 +3202,17 @@ static int claim_swapfile(struct swap_info_struct *si, struct inode *inode)
>   */
>  unsigned long generic_max_swapfile_size(void)
>  {
> -	const softleaf_t entry = swp_entry(0, ~0UL);
> +	softleaf_t entry = swp_entry(0, ~0UL);
> +	const pte_t pte = softleaf_to_pte(entry);
>
> -	return swp_offset(softleaf_from_pte(softleaf_to_pte(entry))) + 1;
> +	/*
> +	* Since the PTE can be an invalid swap entry (i.e. the none PTE), we do

So softleaf_from_pte() returns softleaf_mk_none() instead and causes the
issue?

> +	* this manually.
> +	*/

This comment is not aligned, in case you plan to send this patch as is. :)

> +	entry = __pte_to_swp_entry(pte);
> +	entry = swp_entry(__swp_type(entry), __swp_offset(entry));
> +
> +	return swp_offset(entry) + 1;
>  }
>
>  /* Can be overridden by an architecture for additional checks. */
> --
> 2.51.0

This fix looks good to me. Thanks.

Best Regards,
Yan, Zi