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Tue, 02 Dec 2025 18:54:30 -0800 (PST) MIME-Version: 1.0 References: <20251201093741.730884-1-kartikey406@gmail.com> In-Reply-To: From: Kairui Song Date: Wed, 3 Dec 2025 10:53:51 +0800 X-Gm-Features: AWmQ_bnv2awiqXpmXi1Dz3y0QimTJ-oGJaFqHbWRPMt-fFTe3-SPeHzkO4KAVWI Message-ID: Subject: Re: [PATCH] mm/swapfile: validate swap offset in unuse_pte_range() To: Deepanshu Kartikey Cc: akpm@linux-foundation.org, chrisl@kernel.org, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, YoungJun Park , syzbot+d7bc9ec4a100437aa7a2@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 4B491A0008 X-Rspamd-Server: rspam02 X-Stat-Signature: osntci44mnbgfgc87n9w1uqmic4iuhzi X-Rspam-User: X-HE-Tag: 1764730472-183488 X-HE-Meta: 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 BdSZaKjA sxVxD5WCvb9kRPk3MLpJ9uskBb2yWxhNgGDGSJF8m0PJDpRFmndbZlAy13GA7/vycdaIu5AgbphlO+DOXFeKFbio7mHhfgoecKQfHtdLfp67YRc0Uz7udxxUo7E+rhEM6Ib5IN81nm8dMw4ehp1POq1yVmPAdVrQa+A1I X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Dec 1, 2025 at 6:48=E2=80=AFPM Deepanshu Kartikey wrote: > > Hi Kairui, > > Thank you for the detailed feedback! You are welcome :), > > 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. This one, I think Lorenzo included it or a similar fix along with another fix in swapfile.c: https://lore.kernel.org/all/CAMgjq7AP383YfU3L5ZxJ9U3x-vRPnEkEUtmnPdXD29HiNC= 8OrA@mail.gmail.com/ > > > 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. A sanity check here is acceptable since swapoff is cold and the overhead is hardly visible. No strong opinion on this one.