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bh=wLNoIPFQAdzqlhhDjJljgWkTgIt0PBr/oUCSVxs3Zuo=; b=RyJc3dXVK/dYw+3iTJXMb3qEaBCULjbrWuBFuwA4FABcfAsT/HSJlGN8Q4clstduNeiUBT eArI1L2wvWMx99AQ== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id EA3EC779AA; Fri, 3 Jul 2026 09:19:52 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id UBbKNbh+R2qHaAAAD6G6ig (envelope-from ); Fri, 03 Jul 2026 09:19:52 +0000 Date: Fri, 3 Jul 2026 10:19:51 +0100 From: Pedro Falcato To: Lance Yang Cc: Zi Yan , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, stable@vger.kernel.org, Alexander Viro , Christian Brauner , Jan Kara , Matthew Wilcox , Song Liu , Eric Hagberg , Gregg Leventhal Subject: Re: [PATCH stable] mm/khugepaged: write all dirty file folios when collapsing Message-ID: References: <20260702165409.164568-1-pfalcato@suse.de> <2DA84662-F9E4-4ED3-A225-71054FEC3849@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Action: no action X-Rspamd-Queue-Id: 9A519C0002 X-Rspam-User: X-Rspamd-Server: rspam09 X-Stat-Signature: bpmbuj6nuho34a56q3shq497k8f6wtx9 X-HE-Tag: 1783070397-864802 X-HE-Meta: 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 6w2SQKZV 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jul 03, 2026 at 10:53:24AM +0800, Lance Yang wrote: > > > On 2026/7/3 01:24, Zi Yan wrote: > > On 2 Jul 2026, at 12:54, Pedro Falcato wrote: > > > > > As-is, khugepaged and writable-file opening exclude each other. A file > > > cannot be open writeable and have THPs (because the filesystem is not aware > > > of them). khugepaged will never collapse file pages for files that are > > > opened writeable. On an open(O_RDWR/O_WRONLY), the page cache for that > > > particular file is dropped. This is fine because nothing could've been > > > dirtied. > > > > > > However, there is an edge-case: collapse_file() might not be able to > > > coexist with concurrent writers, but it can coexist with dirty folios > > > (from previous writers). Therefore, the following can happen: > > > > > > open(file, O_RDWR) > > > write(file) > > > close(file) > > > madvise(file_mapping, MADV_COLLAPSE, some non-dirty range) > > > open(file, O_RDWR) > > > nr_thps > 0 > > > truncate_inode_pages() > > > /* THPs are cleared out, but so are the dirty folios */ > > > > > > When this edge-case happens, there is data loss, as the dirty folios are > > > fully discarded. > > > > > > Fix it by fully writing back the page cache (and waiting) when collapsing > > > file THPs. Doing so provides the guarantee that no dirty folio will be > > > observed while there are active THPs. To fully ensure this is safe, the > > > invalidate_lock needs to be held while doing the writeout, so that > > > do_dentry_open()'s page cache truncation excludes this write-and-wait. > > > > > > Cc: stable@vger.kernel.org > > > Cc: Alexander Viro > > > Cc: Christian Brauner > > > Cc: Jan Kara > > > Cc: Matthew Wilcox > > > Cc: Song Liu > > > Cc: Eric Hagberg > > > Cc: Zi Yan > > > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") > > > Reported-by: Gregg Leventhal > > > Closes: https://lore.kernel.org/linux-mm/CAFN_u7H_0ECF3jixP=T=U7AH5=Q3wQNvJMo8an3VqUDMerQfUw@mail.gmail.com/ > > > Tested-by: Zi Yan > > > Signed-off-by: Pedro Falcato > > > --- > > > This patch is written against 7.1.0 (because the code no longer exists in mainline). > > > > > > Zi, I kept your Tested-by, but I had to move some things around and > > > use the invalidate lock. Please re-test if you can. > > > > Tested it again on top of v6.12 (the patch applied cleanly) and the issue > > is gone. My Tested-by still holds. :) Awesome, thanks Zi! > > Since READ_ONLY_THP_FOR_FS is gone from mainline, just to confirm: does this > only affect stable kernels, right? Correct, current mainline doesn't play any sort of fun games with truncation and the code is fully gone from do_dentry_open(). -- Pedro