From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793131673; b=gFtf2p0v6OKffIVKYcauBaPYm1ZoP1RHxT8jo7EDgK4nyP0bdqGItTF0Ew6iMV9JyO4s Sbk7C10HpeWtSH1DhWEdItJVjD9yGFd2YoMUR/Voju63WLUpEC84td7Dl+zaySq6nXji6 1LOAVD3IvLHg9FZuSJKfUVJ8SWcSK2TieDOqV/t/6RFYm9NW08d2YrBAANU47K4LbJ1yz xvzSDTmZG/vljSWm24+i+ZHubL/LRvtH/LFP79F7Zyc+Z52FRO7DTbGep/RyUpIYZN4oM EAxjbVkQ4kosuUpfSdUXh6LM2bWmmykJAsNGkLL8RPrDIVc7roFcQWlMs2YKK3j9C8A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793131673; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=7GmJ1pURkrI2M4cFdKYZZ2Ya/fgG59abQ7Yb/9UtrSs=; b=grGIG09/DaCOnGAMbqvOnb7mJxeDeUh1WMKGDdcL+O1OLQpNRGGKk5ZIrXUj8ZvziN9A PFIqVU5tVVKxYA8XksX9cB48OTwy4bA2ZXRZBxl1dX2hA30cpElbWi5dUK4HMEpl9O8k9 E4XxcXNBu7CTZuTMbFABCYAOEt3lIlWDtxmN2d9EKqFuvwkDfVpc9LdYpOcynjbYnAOaR UPXWlxCIiPgDdbi5ADQjk2DTgTf91chF/fW8dp69NvWT+0LujgmDSS54OfuMXwCSpvVRW 7wBmjluefI3OQikua9P8tlFeEiWcSg78b95gizNQMxrnfvI3KtG2kc4Sbign/74PE3A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b="f/91R5wp"; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8AA55606A31A; Tue, 27 Oct 2026 20:07:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=f/91R5wp Received: by smtp.kernel.org (Postfix) with ESMTPSA id B5CF11F01825; Tue, 27 Oct 2026 20:07:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793131673; bh=7GmJ1pURkrI2M4cFdKYZZ2Ya/fgG59abQ7Yb/9UtrSs=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=f/91R5wprezD4KJkX2Jx7eMJXK4zGt7nCjRBu4zWgh8B2lozTbjxHynKIIEt9/m3f KmyPkE3l8j/1agfXZbGkBypO2fHwU0XhSfNULcLHjxjA52K9g29144aOXDupqH3gVj OT3eLlqbs0BTCVZVhirng7gxbOWPZ8yfKPk5IvDDERvJBacYahHrZc6ze7rglgM8w6 imkuTFKf8yCjOjgLHdSu9sDjLJshaUz/ScopTOXRxeyoDso5ip229Mq5ygKszg6hf8 HikkJKqYHXvk2V7qmSpaCnNcIPX5qKKye2psG5orwcoufcMa2jqaetc2Dy2c7kS6jc 2bZ5YYFxsJP3g== Date: Tue, 27 Oct 2026 20:07:51 +0000 From: Harry Yoo 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 , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , 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, Josef Bacik , stable@vger.kernel.org Subject: Re: [PATCH 01/46] mm/mglru: don't use stack pointers when walking PUD and PMD tables Message-ID: References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-1-6f74bec9a5bb@kernel.org> X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261027-fixes_core-v1-1-6f74bec9a5bb@kernel.org> On Tue, Oct 27, 2026 at 12:17:21AM +0100, David Hildenbrand (Arm) wrote: > From: Josef Bacik > > MGLRU passes stack copies of page-table entries in walk_pud_range() and > walk_pmd_range() when walking to the next level. These copies can become > stale when khugepaged or MADV_DONTNEED (CONFIG_PT_RECLAIM) removes a PTE > table concurrently. > > This pattern dates back to commit bd74fdaea146 ("mm: multi-gen LRU: > support page table walks"). Likely, earlier locking masked the latent > bug. Later changes exposed it: commit 1d65b771bc08 ("mm/khugepaged: > retract_page_tables() without mmap or vma lock") allowed concurrent > retraction, and commit cf4a65539c13 ("memcg-v1: no need for memcg locking > for MGLRU") dropped the walker's outer RCU protection. > > The fix is simple, so just fix the original commit so we don't have to > speculate. To fix it, pass the actual PMD/PUD pointers. This restores the > RCU-protected lookup and validation against the live PMD. Note that the PUD > handling is required as well to handle folded page tables correctly in all > cases. > > Fix generated by an LLM and sent by Josef Bacik in private. > > Fixes: bd74fdaea146 ("mm: multi-gen LRU: support page table walks") > Cc: stable@vger.kernel.org > Signed-off-by: Josef Bacik > [ david: handle walk_pud_range() as well, clarify+simplify description, > adjust Fixes: ] > Signed-off-by: David Hildenbrand (Arm) > --- Looks good to me, Reviewed-by: Harry Yoo (Meta) -- Cheers, Harry / Hyeonggon