From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.152 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793070333; b=b1sN6ahMv8j+Ngag7u6QqbQEqjq62P8Rn5U43WZ39so2dW5rFORczJWVSCS5vUchwwyD llfgPsgDR28/vwWCfxEgne2SW7/aMJumtCSFpaYLL6r3nlrMVeX9qjgoHD9cNmysULbkD RMM0jo28SfOLKXtL6O1gVTRwVDEfj4myYgdfInUg9mxv4f9iVzvGEkDVmdltRGrMHKWqL GAEgbP2gSwco+II+G3UGYH3V4VF4UVDRUNu3qpKDZ0B3VT+hCW1gMy7+++A5IhqUoo7F/ oLADmMSoCn0mpEZcg3cu+7c7Ilg1A/TWBoeuvHVxPQ3CG5KLY/uAPkcILVB0jQLbJBQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793070333; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:In-Reply-To:Content-Type: Content-Transfer-Encoding; bh=S2fYp0D+kux7GkOrzGv4DxJUQ1pHehCh6wWsm9VP8mw=; b=t0HFGBrPFp/XEn+eHrAR2+gHix7u7ayoDkYmurgUBrp++1h875nbLW+62PWxjJXYwDDI pzH8IHJ6+mFtZo9j+6NLZLUx+oC7AmWa2xCsFIDzPpDCOwv4paRuqXz9Edq6zRK6zmy+U uC7NeNO/eHt2sqeeD/1wDkha0JU5kdH+Jjli5vsMQcs83bJCMFq/jSeR5UsPub2TQG1RA b2shH48Yh4SrSuSM0do+gxc1L9O9RfYL9HWJs1jdLzEikFPredJgjkvjGBipIxO41ir88 mipmyt0iwol970VBMPKjupdgr252EjMLb5TvEB5gBtURmuVvLOM8DAVBnR3FyRAZZkA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=c65rOCZf; arc=none smtp.remote-ip=95.215.58.152 Received: from mta1.migadu.com (out-152.mta1.migadu.com [95.215.58.152]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 711F2606A31D for ; Tue, 27 Oct 2026 03:05:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 711F2606A31D Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=c65rOCZf X-Envelope-To: linux-cxl@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=PpgTbepyGCQbdry0Tl9jwBnnjb4CaWXJ3ss5elRPGCc=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793070330; v=1; x=1793675130; b=c65rOCZf1Vlq0GQPAQmQqm5wf83ltLhRtUxYonNAqk4jRy4mWveQ6FYHE0z2KgSx0vBBuhwh I5BSaMM8kbNm5zMj9kh6fIQDiuHKd5Weox4bLMD3rtVDFQIbo7eTm65U5091811U3kGr9K6AGAx 2ioEyZte5hznqL0+wFow5F8A= X-Envelope-To: linux-cxl@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 9170fb527649b4ac; Tue, 27 Oct 2026 03:05:20 +0000 X-Mizu-Trace-ID: 9170fb527649b4ac X-Migadu-Flow: FLOW_OUT Message-ID: <62dfb28c-1078-440e-ba23-9068f4958570@linux.dev> Date: Tue, 27 Oct 2026 11:05:01 +0800 X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 01/46] mm/mglru: don't use stack pointers when walking PUD and PMD tables To: "David Hildenbrand (Arm)" , Andrew Morton , Johannes Weiner , Michal Hocko , 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 , 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 Cc: 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 References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-1-6f74bec9a5bb@kernel.org> From: Qi Zheng In-Reply-To: <20261027-fixes_core-v1-1-6f74bec9a5bb@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10/27/26 7:17 AM, 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) > --- > mm/vmscan.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) Reviewed-by: Qi Zheng Thanks, Qi