From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 619EF4756B5 for ; Tue, 22 Sep 2026 13:48:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790084898; cv=none; b=eM1Hn/AMlzKSjexO8UabRkFSS8TD5NAS32OpmmH5kuQ1+7FhIeNfu0t8cOusP2pS4/vZkdH7ptiyV0nk47ZXUx/RBgdIui9mKTB40viwUaM6qeLdM0dKprHAtYPb5RhwJwDPrmLAENfvCBpP8Q3zPonrX/PpW1lGY9ZvvenxI6Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790084898; c=relaxed/simple; bh=w10RBxsUGtOFHpPwTlagk7zihbsxVZOw5yPuLYb1AY8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=FSHoXX3lquuhT/GTx8jJ0k+UAKSplcephEIjH1fXmcJE8qYjrKtSA5CRC9zMkHGHWNEDaSlzva/oQftU6g6pMKHMAvNwuOM8ifvMh6tjtYyNrfxM+R8TZ04VLOUqtsXzh0J67ym8DTCtPW+YfJDxNPb11GF0ez3y4WtPkRVo/CQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=iqMOITd1; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="iqMOITd1" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1790084895; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=6IrbNKYXaxBgTnuatiYDHte9IqTtxWZJRiUhRvSTwak=; b=iqMOITd13xmvy/DSRXNUxqAiQOVd+tftAh5Y3r7hWqjrmQpW3jDjj/9oG0EJkRbLbCbZoZ C9gW3Mo1g61XVInuxlKF0vj8MHAcnvlvCtnEaOUdqpn7W4D5x3MI5bF6QqSZd7NaWuXd1c opiQpHnwdcnk7dMMmdnKXFOyt1AuV8w= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-299--PafZw6uO163-ZRW7g_LJA-1; 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260922110703.468389-1-yi.zhang@huaweicloud.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 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 >