linux-kernel - Re: [PATCH] mm/swapfile: validate swap offset in unuse_pte

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Message-ID: <CADhLXY73pZGTvV_2wmCB0WUOecAtrcwOBoBJQc42CQ8MOBMjJA@mail.gmail.com>
Date: Mon, 1 Dec 2025 16:18:39 +0530
From: Deepanshu Kartikey <kartikey406@...il.com>
To: Kairui Song <ryncsn@...il.com>
Cc: akpm@...ux-foundation.org, chrisl@...nel.org, shikemeng@...weicloud.com, 
	nphamcs@...il.com, bhe@...hat.com, baohua@...nel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, YoungJun Park <youngjun.park@....com>, 
	syzbot+d7bc9ec4a100437aa7a2@...kaller.appspotmail.com
Subject: Re: [PATCH] mm/swapfile: validate swap offset in unuse_pte_range()

Hi Kairui,

Thank you for the detailed feedback!

> But it seems the report is no longer triggering after the softleaf v3
> change right? Checking the syzbot link, last reproduce was 11/11

You're right - I should have checked the syzbot status more carefully.
If softleaf v3 has already fixed this, then this patch may not be
needed.

Could you point me to which specific change in softleaf v3 fixed it?
I'd like to understand the root cause better.

> What kind of race will lead to a invalid swap entry in the page table?

You make a good point. I was speculating about possible causes without
concrete evidence.

> I'm not against a sanity check like this though, just want to double
> check before we process.

If softleaf v3 has fixed the underlying issue, I can withdraw this
patch. Or if you think a defensive sanity check still has value, I can
update the commit message to reflect that it is defensive hardening
rather than a fix for an active bug.

Please let me know how you'd like to proceed.

Thanks,
Deepanshu