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Fri, 30 Oct 2026 13:13:04 -0400 (EDT) Date: Fri, 30 Oct 2026 17:13:03 +0000 From: Kiryl Shutsemau To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, stable@vger.kernel.org, Josef Bacik Subject: Re: [PATCH v2 05/47] mm/truncate: look again if a folio left the mapping Message-ID: References: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> <20261029-fixes_core-v2-5-a64ce7f83abb@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261029-fixes_core-v2-5-a64ce7f83abb@kernel.org> X-Stat-Signature: fe5z9kh9cnp8sr1jbh7xqpwipehdozwj X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: CCCF3C000C X-Rspam-User: X-HE-Tag: 1793380403-587602 X-HE-Meta: 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 scTKozoS alzlYJ2R4G3y94phiCgnTHr+5UJ5MqziSS67x/ceNG4hQ5nvXqIl/L/YKzoUKA5CGhYT7UFhbdrsCvfBDUr/EZQiP1AXPV3Kcl2ZgKqho8SMeqo9uWAjHmzdBhIzPLjHdJSzTDralsAzQPvwG5WSQBkyzDq/BpJq2GU2EmrTEMhEGwXqVxaj9aBhg+ZpmJRsxl5/hfD0QXWEPSaHnTujkSUEW7xZeOILVg3DZN13U3sOS+XDNHpclJgC1i7Xcw32jiKK9SyN8N00FWHypp0lD9Lb8wbmQ+IPSNiJ4wNa8vLDvxT/job7GE+rAwbcedTA9coHqHDmDVM4JNXm2yZ0/OeIVEfVNeKhLPvDqis3A63begML/qW/y6+3D191Dv/442+y+DXsy//mGxO4rWLlzRzd9x0ojiEUSV37b08edleDKAOXw1a01UfDExsdbQamNPOZG5HR5+1fXS17pxKfO/6HiboDf803ZAfmMxvPb6P0X4cI+6IxNVPT/LlNqPp7iS7RJjkXD/j64n/U= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Thu, Oct 29, 2026 at 09:33:00PM +0100, David Hildenbrand (Arm) wrote: > invalidate_inode_pages2_range() skips a folio which no longer belongs to > the mapping by the time it has got the folio lock, on the assumption > that somebody else has removed it from the page cache. But the folio may > have been replaced, and then there is a new folio with the same data at > that index. > > For most cases, like folio migration, that is impossible. However, > collapse_file() only checks the refcount of the old folios, under the > i_pages lock, and relies on their folio locks from there on. That works for > users which repeat the lookup when they find folio->mapping changed. > The following scenario is, however, possible: > > CPU0 pwrite(O_DIRECT) CPU1 collapse_file() > kiocb_invalidate_pages() > read the folio (old data), lock it > refcount check > the write completes copy to new_folio > kiocb_invalidate_post_direct_write() > find_get_entries() -> old folio > xas_store(new_folio) > folio->mapping = NULL > folio_unlock(folio) > folio_lock() > folio->mapping != mapping > -> continue > > In that scenario, the collapsed folio with the data from before the write > stays in the page cache after the write has returned. > > This used to be impossible, as khugepaged only collapsed files that nobody > had open for writing. > > Restart the lookup at that index, like shmem_undo_range() does. The same > problem seems to exist in truncate_inode_pages_range() as well when > truncate_inode_folio() fails, so handle it there as well, but slightly > differently: simply check once more through find_get_entries(). > > Fixes: 1b6444331beb ("mm/khugepaged: enable clean pagecache folio collapse for writable files") > Cc: stable@vger.kernel.org > Reported-by: Josef Bacik > Reviewed-by: Rik van Riel > Signed-off-by: David Hildenbrand (Arm) Reviewed-by: Kiryl Shutsemau (Meta) -- Kiryl Shutsemau / Kirill A. Shutemov