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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776586808; bh=ULzAcQ+a5yvU6pSydPbcp5Zrd7MaFUBLpohDNl0zto0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=jY1BPD2lU1Iqz7fd/hrVI4VR2mnaRy7YSp0qiFqQOF0egxnj5OfsXl3VHc08ncjvI asjBFqyyeELe0U0CCDnkgUJR0mODASwcvBUzKoES8ge/b+a1qZvz3iIetDqro/3YDu Zg02sSy2I3l4Su32OyEciZ0z5J59oy8kplSRsUYomBpiTdD3/Q1nwPqfACTsEAVV4p XZf2q3y2Jd1WUC5Ufo9hi9pJ9nEb1SUQnEOr/PpZKBHbOxRBnCR9+gax7lR7xAtGwR Z+POE2aqz4butePJg6YNOjC5/d+6Na02UjwzpBHf2MdIdClFBq6oINoybXTMYCZ17B JlqfByBVk1D3Q== Message-ID: <7b983108-4846-46ce-b9f5-2aef319c00dd@kernel.org> Date: Sun, 19 Apr 2026 10:19:59 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: prepare anon_vma before swapin rmap To: Lorenzo Stoakes Cc: ZhengYuan Huang , 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 References: <20260417011606.1089985-1-gality369@gmail.com> <66f67e51-819b-4c60-9f61-170db32362a2@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Stat-Signature: izb9wsucms4sz5mb4doebopgcgud6enc X-Rspam-User: X-Rspamd-Queue-Id: F00EFC0009 X-HE-Tag: 1776586809-914914 X-HE-Meta: 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 /vC0XRoO pqBUxdHwHH082kk5+bOn0592av9Z2pSsF6zTEr2+HXJF3FTlW/8t4KHaHtEkP7z4jA6dsfzqxYTs0dWhZEBDV6dd2jNgJWd8pS3C6RFkHF+UACG9iTB64K2s2iezprxo9LVGfawk4HpfSmxW/CCaVKyrHzTOdG1+cCaQDxr833sCNznIql9PRJeEjqOQLxOVnWNf7cpErAGVY1YIrh4RMSyTxPcqHx5qJ2T5rMiGgKuvhagaNs0AaoL+rdM25H2xEJMe0NIIp8qnjmMZ1Vlob4Ip/0GsD/EA0Nv9wNSIE7XIcxyz+79eF1AwflLjq8719CvI+g3eEoaPOPXc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/18/26 11:35, Lorenzo Stoakes wrote: > On Fri, Apr 17, 2026 at 01:57:59PM +0200, David Hildenbrand (Arm) wrote: >> Maybe there was a scenario where we could have lost vma->anon_vma during >> a merge, resulting in a swapped page in an anon_vma. > > Unless there's a bug (and correct me if I'm misinterpreting), VMA merge 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. The reporter claimed that it happened on 6.18. Nobody knows on which patch 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 too that went into 6.19 might have resolved this problem. Your fix stated "allow an unfaulted/faulted merge with a VMA that has been forked", so I was wondering whether that could have resulted in a situation with anon folios without vma->anon_vma (losing vma->anon_vma during the merge). But I am not sure if 879bca0a2c4f could have triggered that. Are you aware of other fixes that went into 6.19 that could have fixed such a scenario? -- Cheers, David