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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1u9Cbm-00000004mKZ-1iAF; Mon, 28 Apr 2025 00:44:30 +0000 Date: Mon, 28 Apr 2025 01:44:30 +0100 From: Matthew Wilcox To: Kairui Song Cc: linux-mm@kvack.org, Andrew Morton , David Hildenbrand , Hugh Dickins , Chris Li , Yosry Ahmed , "Huang, Ying" , Nhat Pham , Johannes Weiner , linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/6] filemap: do not use folio_contains for swap cache folios Message-ID: References: <20250427185908.90450-1-ryncsn@gmail.com> <20250427185908.90450-5-ryncsn@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250427185908.90450-5-ryncsn@gmail.com> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 984FC40002 X-Stat-Signature: 5owsyfsnew8fxzcy9wyoai1apub1mxc4 X-Rspam-User: X-HE-Tag: 1745801085-405213 X-HE-Meta: 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 kvRviKy+ sioZhZ41/3YbJb6c/ndHBs8axErt7Plo1fYxHx2uSvM3JE/kZad5xqzXpwYc0AvqF3wXI59feLatQjt22oYkCQu2RN95Yy1MqxXewbICWmEPyeg8XvqsUkCDQEgRtNcocN8tMxFD6OChfyfBGG0dL5KqP+w3LxKSV4EWwcYGPvp5OHmnKJ2a+911xTJZi3QEKLJPiN9jlXJhAMltiYjhlbpuqqy/zdV7TsHp0wVwH3uP0m96ku5eRFM66TtdGR3L3/a+KqNjvKcNHMyKnmRHKEVSIbQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Apr 28, 2025 at 02:59:06AM +0800, Kairui Song wrote: > For filemap and truncate, folio_contains is only used for sanity checks > to verify the folio index matches the expected lookup/invalidation target. > The swap cache does not utilize filemap or truncate helpers in ways that > would trigger these checks, as it mostly implements its own cache management. > > Shmem won't interact with these sanity checks either unless thing went > wrong, it would directly trigger a BUG, because swap cache index are > unrelated to shmem index, and would almost certainly mismatch (unless > on collide). It does happen though. If shmem is writing the folio to swap at the same time that the file containing the folio is being truncated, we can hit this. > - * Context: The caller should have the page locked in order to prevent > - * (eg) shmem from moving the page between the page cache and swap cache > - * and changing its index in the middle of the operation. > + * Context: The caller should ensure folio->index is stable and it's > + * not added to the swap cache. I do think we need to keep the part about the folio being locked.