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Received: from 30.74.144.121(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0X6mK60X_1783655330 cluster:ay36) by smtp.aliyun-inc.com; Fri, 10 Jul 2026 11:48:50 +0800 Message-ID: Date: Fri, 10 Jul 2026 11:48:49 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH stable v2] mm/khugepaged: write all dirty file folios when collapsing To: Pedro Falcato , Andrew Morton , David Hildenbrand , Lorenzo Stoakes Cc: stable@vger.kernel.org, Alexander Viro , Christian Brauner , Jan Kara , Matthew Wilcox , Song Liu , Eric Hagberg , Zi Yan , Gregg Leventhal , Lance Yang , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260708151357.353173-1-pfalcato@suse.de> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 4C64940007 X-Stat-Signature: tnn17w3x5kgwzmd7c8wc1euiewhh554y X-Rspam-User: X-HE-Tag: 1783655335-155632 X-HE-Meta: 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 eJRHKZqd 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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 7/9/26 12:28 AM, Pedro Falcato wrote: > Seems that I accidentally dropped linked list Cc's here, see > https://lore.kernel.org/stable/20260708151357.353173-1-pfalcato@suse.de/ > > On Wed, Jul 08, 2026 at 04:13:57PM +0100, Pedro Falcato wrote: >> [There is no upstream commit, as this code was removed by upstream >> commit 044925f9b565 ("mm: fs: remove filemap_nr_thps*() functions and their users")] >> >> 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. >> >> As a side effect, move the nr_thps counter bumping outside the i_pages >> lock. This is correct since the counter itself is an atomic_t and the >> producer <-> consumer correctness is provided by a full memory barrier: >> smp_mb() in collapse_file()/memory barrier implied by full ordering in >> get_write_access() -> atomic_inc_unless_negative(). >> >> 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 >> Tested-by: Lance Yang >> Signed-off-by: Pedro Falcato >> --- LGTM. Thanks. Reviewed-by: Baolin Wang