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Tue, 22 Sep 2026 09:48:11 -0400 X-MC-Unique: -PafZw6uO163-ZRW7g_LJA-1 X-Mimecast-MFC-AGG-ID: -PafZw6uO163-ZRW7g_LJA_1790084888 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 6E1E8183090D; Tue, 22 Sep 2026 13:48:06 +0000 (UTC) Received: from bfoster (headnet05.pony-001.prod.iad2.dc.redhat.com [10.2.32.117]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 6486930001B9; Tue, 22 Sep 2026 13:48:00 +0000 (UTC) Date: Tue, 22 Sep 2026 09:47:58 -0400 From: Brian Foster To: Zhang Yi Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org, akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, hughd@google.com, baolin.wang@linux.alibaba.com, willy@infradead.org, jack@suse.cz, ziy@nvidia.com, joannelkoong@gmail.com, djwong@kernel.org, yi.zhang@huawei.com, yizhang089@gmail.com, yangerkun@huawei.com, chengzhihao1@huawei.com, wangkefeng.wang@huawei.com, yukuai@fnnas.com Subject: Re: [PATCH v4 0/4] mm/truncate: fix data loss when truncating straddling large folios Message-ID: References: <20260922110703.468389-1-yi.zhang@huaweicloud.com> MIME-Version: 1.0 In-Reply-To: <20260922110703.468389-1-yi.zhang@huaweicloud.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Mimecast-MFC-PROC-ID: JnpoQaYqlk9rQqeUGc8JClMlZrxrm6M23EtYSDeakHI_1790084888 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 2522340013 X-Stat-Signature: 6u83cbp1pmy87a1c77xaukgzkkg6zigp X-HE-Tag: 1790084896-173760 X-HE-Meta: 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 7KtK2zQk 8xYCrlTS2l5+SjaaSMdJTeaj0lfTYmUsByzJd3k+SIbjRR8BvQ0NUKgiK9ebRrEXD00TxikisWHA2Y1fSDOka7oI71kv8m40T+ThbtVBPZed6q4KQX2SqgWj5evIH6eWyqaAhRgTga2gToBBcIxMshBXiajkc9/3rSQtEsG9RwEqrOvL1Q0bPc7TzxvjI141CaZ47+Cr+g8/9ohNfqlvOev45WJMZ3ZXqPmfb+T2eLUR6mqWtOujR8ABvipC10/jFoCVGHcMrthberX9Om03FSTF39U0zV1aqhNZE/Ml7XCGW5TKfNQ/5AfTExed6L41qiQLwSW9P4mXot1meAY7i6o0AeIdaNXk5LPbgosApT6OO/IZKYv8bDeUsNICrsOsR9wso8jXJDlvRTrsKCy2O07vB1cjKSK3jUVPpioiR9vk+cB6pUdneRMVOvjfSigCwWa3IsY9ACTjoGZbPnKCGnfEzBg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 22, 2026 at 07:06:59PM +0800, Zhang Yi wrote: > From: Zhang Yi > > Hello, > > This is the fourth version fixing data loss when truncating straddling > large folios caught on the upcomming ext4 + iomap buffered I/O > conversion. > > When truncate_inode_pages_range() punches a hole or truncates a file, > truncate_inode_partial_folio() splits a large folio so that the caller > can drop the in-range sub-folios while keeping the out-of-range tail > intact. This series fixes three distinct problems in that path that > can each lose the valid out-of-range tail of a straddling folio, plus a > follow-up that clarifies the return value semantics. > > Patch 01 aligns the truncation boundaries inwards to the mapping minimum > folio order in truncate_inode_pages_range(). With a non-zero min_order, > folio_split() stops at min_order instead of order 0, so a boundary > computed at page granularity can land inside a min-order-aligned > sub-folio and the truncate loop drops that whole chunk, valid tail > included, causing data loss. > > Patch 02 looks the end-edge straddler up by its page index through > __filemap_get_folio() in truncate_inode_partial_folio(). After the > first split the straddler is unlocked and only transiently ref'd in the > page cache, so the page pointer derived from the original folio can be > freed and reallocated as a different folio in the same mapping, and the > mapping check cannot catch it, which may cause incorrect splitting and > potential data loss. > > Patch 03 reworks the contract between truncate_inode_partial_folio() and > its callers. If the second split of the straddler fails, the function > reported success unconditionally, and the leftover incorrect end > position could cause the truncate loop to drop that valid tail. After > rework, it tells the caller the exact page range safe to discard via new > pstart/pend out-parameters, so the truncate loop never touches a > straddling folio that still holds valid out-of-range data. > > Patch 04 clarifies the return value semantics to "at least one split > succeeded", which is all the shmem caller needs to decide whether to > reset its scan loop. > > > The second patch fixes a pre-existing race issue that is reachable > today, so it is Cc'd to stable. Patches 01 and 03 require a dirty large > folio that carries no filesystem private data, so they are not reachable > on current filesystems. They were found while developing the upcoming > ext4 iomap buffered I/O path[1]. > > Thanks, > Yi. > Hi Yi, Modulo Jan's comment on patch 4, this series looks good to me. FWIW: Reviewed-by: Brian Foster Brian > [1] https://lore.kernel.org/linux-fsdevel/a638a8fb-c184-4069-ae33-379ec12cd514@huaweicloud.com/ > > > v3->v4: > - Move the patch that fixes data loss when min_order is non-zero to the > first patch position, aligning start and end in > truncate_inode_pages_range(). (Zi Yan) > - Add patch 2, fixing the invalid folio2 issue under concurrency when > truncate_inode_partial_folio() splits at the end position. Use > __filemap_get_folio() to obtain a reliable folio2. (Jan Kara) > > v2->v3: > - Rework the folio2 validity check logic to fix the invalid > folio->index issue. (sashiko) > - Clarify the pstart and pend setting logic and the corresponding > comments to make it more readable. (Brian, Joanne) > - Split the patch into 3 small patches. (Zi Yan) > > v1->v2: > - Export pstart as a new parameter so that the generic and shmem > truncate paths don't need to recompute the start value from the > return value. (Brian) > - When min_order is non-zero, align [pstart, pend] to the inner > boundaries of the folio to ensure they do not point into the middle > of a large folio, which could otherwise cause valid data within the > folio to be incorrectly cleared. (Joanne) > > v3: https://lore.kernel.org/linux-mm/20260916092450.654408-1-yi.zhang@huaweicloud.com/ > v2: https://lore.kernel.org/linux-mm/20260909062339.473816-1-yi.zhang@huaweicloud.com/ > v1: https://lore.kernel.org/linux-mm/20260903115018.2034541-1-yi.zhang@huaweicloud.com/ > > > Zhang Yi (4): > mm/truncate: align truncation boundaries to mapping minimum folio > order > mm/truncate: look up the end-edge straddler by index > mm/truncate: fix data loss when splitting straddling large folios > fails > mm/truncate: clarify return value of truncate_inode_partial_folio() > > mm/internal.h | 4 +- > mm/shmem.c | 13 ++--- > mm/truncate.c | 128 +++++++++++++++++++++++++++++++++----------------- > 3 files changed, 91 insertions(+), 54 deletions(-) > > -- > 2.54.0 >