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Wed, 22 Apr 2026 01:00:25 -0700 (PDT) MIME-Version: 1.0 References: <20260417011606.1089985-1-gality369@gmail.com> <66f67e51-819b-4c60-9f61-170db32362a2@kernel.org> <7b983108-4846-46ce-b9f5-2aef319c00dd@kernel.org> In-Reply-To: From: ZhengYuan Huang Date: Wed, 22 Apr 2026 15:59:57 +0800 X-Gm-Features: AQROBzAQnd6fQm_0AX9PB7FoGOcVs_JigoJGga_0OB8c5jLDr8Q7qLkyQ_nymDw Message-ID: Subject: Re: [PATCH] mm: prepare anon_vma before swapin rmap To: Lorenzo Stoakes Cc: "David Hildenbrand (Arm)" , akpm@linux-foundation.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, r33s3n6@gmail.com, zzzccc427@gmail.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 0A653A0017 X-Stat-Signature: j7korpoh41s4morjtnmf76hrxbe1a3nw X-Rspam-User: X-HE-Tag: 1776844827-837636 X-HE-Meta: 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 5FTlHwXe fpe6kxrZe7Zb7GkWs6LL/E9z6NxdHbP0U5x2KfVuu2qlAfkO82QVOoMIc2qx+Mb0JV5FqL8lxyVMsdBwzVHh3dZEFyzY19Uzj8d9RldXsUE6udT0EB4OVpTBhT7tHPQf7NNWV59T0PbWS2oX56ss7Vr3CWWfdsMeDVIEONJi00Kaetqs9nNsMDfcbZDNiPXIA4SI2y2HYsCqoiWK94HT8/+l0VorUGuW6cKynuyaPM6KpXK6biEN4YIVjET46bQM06jJ4xCh2NFLZVMMmaZqbnD6TJRemoSTmMeaYbt+J5G+nXvn2RRW1Cm2L0EOFf3CdFp33QApqxFV5FYaid6tZXGr4hCIXQQ8zjF2UBoKkg5zOK85cHkyvVNXYtipaHP/b2ouHMTO8O/4A5K5ThRjg9XyAgSZnKTB1HpMkDRUyQoRhIGPf0Ewh9E/WKsehCvtwuJkgRvjw6ceTfuZ6kxGSbjjU/1aiATG+BQdB/LqilY2+0OhykCPstF1F/vnnbDFDbdUzCI0aZowBjuaGntMHzV4NLw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Apr 19, 2026 at 10:21=E2=80=AFPM Lorenzo Stoakes w= rote: > > On Sun, Apr 19, 2026 at 10:19:59AM +0200, David Hildenbrand (Arm) wrote: > > On 4/18/26 11:35, Lorenzo Stoakes wrote: > > > On Fri, Apr 17, 2026 at 01:57:59PM +0200, David Hildenbrand (Arm) wro= te: > > > > Maybe there was a scenario where we could have lost vma->anon_vma d= uring > > > > a merge, resulting in a swapped page in an anon_vma. > > > > > > Unless there's a bug (and correct me if I'm misinterpreting), VMA mer= ge requires > > > vma->anon_vma to either be equal for merged adjacent VMAs, or one or = the other > > > VMA to have NULL vma->anon_vma, in which case we set vma->anon_vma in= the merged > > > VMA. > > > > I think you didn't understand what I was trying to say. > > Let me take more of a look then! > > > > > The reporter claimed that it happened on 6.18. Nobody knows on which pa= tch > > version (stable tree?). > > > > I was wondering whether your fix > > > > commit 3b617fd3d317bf9dd7e2c233e56eafef05734c9d > > Author: Lorenzo Stoakes > > Date: Mon Jan 5 20:11:49 2026 +0000 > > > > mm/vma: enforce VMA fork limit on unfaulted,faulted mremap merge to= o > > > > that went into 6.19 might have resolved this problem. > > Ahhh, no not that one (it affects merge of VMAs that have a CoW hierarchy= which > we shouldn't allow) but 61f67c230a5e actually could cause this. > > Can see from https://kernel.dance/#61f67c230a5e it was backported to 6.18= .7 I > think. > > ZhengYuan - can you try seeing if it repro's with/without that? > > If you're testing literally at v6.18 in Linus's tree say and NOT on a sta= ble > tree, then that's your problem - you're essentially testing a known-buggy= kernel > (we always find stuff later and send to stable, just how it is). I can reproduce the issue on 6.18.7, but I can no longer reproduce it on 6.= 18.8. So it does look like the problem has already been fixed by commit 61f67c230= a5e. Thanks everyone for the insights and pointers. This issue was originally found by our fuzzing tool. Unfortunately, our reproducer generation is still a bit unreliable, so I cannot provide a standalone reproducer at the moment. However, given that the issue appears to be fixed, I suppose that is no longer strictly necessary. Let me know if further testing is needed. Thanks, ZhengYuan Huang