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=1794312713; b=Z8YGWNlQbWvRtA9Vo1LYvdef1AaT9L1sKmD/b5cEagqW0kfWN5jqyGsJGpbbqqraf7+b hpfNSd2N05Zi6ZQx2XSA6w2mgb1wZJlqTZVhMEBAKPCfon9mUGTlKnx39eoIRVr7RVKA3 j2hwuhjD0Ey0+auZ1b5u7y214I7f8/fIIY0/XiAUAg8CWmywB9mU1XOIVA+tQekSm3W9J 0Z2DAv5OOgSOYWxl/moT3Oc5UPhwQ99L2ZGuclPII7uFGBuWGWEdzsr9DS51snwVtCNYn nNUhmuPeEHAnDxM4mkBwT9b7CTC5FXc68xGpeOwuh9WSdzt+4DPwrh6R78HksbKOrOw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794312713; h=Received:DKIM-Signature:Received:Received:X-ME-Sender:X-ME-Received: X-ME-Proxy-Cause:X-ME-Proxy:Feedback-ID:Received:Date:From:To:Cc: Subject:Message-ID:References:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; bh=J48t8mCWZ0Ly4qztcbrxqVse8BQ1Um1Gqa5tCIqH990=; b=s6EVPh5qB8/3k7aZd0l2reH4jv4QZAO8gvSf7S1nOC6u9BtMW78J+YRiO0FzmOZwk3eI +lfSSlKxoQMYHHPHPNFTA9E7nWA+v3hTPhuNemezwlPcu1aZjda144Y1vJk5a+L55fjg3 cD5a3cDNSiZ5jpBE3UTGnUAxkLlDFcc0Hp7/52cpqaUd5Mm9g8IcaWg5u0Vfj8SH+4+uP MUEzMZ2euYcNx8Cp7sydi9YYTYDTXEMoFffYVxyEF8esBV1hGprEQureFVJft3kQYwznh ErXqMGLVPO04KRXjv/KPdJ91rZS1B+QsDLG98XoLkuMZDMAPlRmjE2rKRQzFq3b/Jkg== 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="hiU/JVKX"; 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 48802606A325 for ; Tue, 10 Nov 2026 12:11:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=hiU/JVKX Received: by smtp.kernel.org (Postfix) with ESMTPSA id E57CF1F008A2; Tue, 10 Nov 2026 12:11:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794312712; bh=J48t8mCWZ0Ly4qztcbrxqVse8BQ1Um1Gqa5tCIqH990=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=hiU/JVKXRON4pPovCVkTdBfU1F2AHh9WpLK0LoUtYTmH7G0CHrn3ufdzdom+ZHOVp YVgzhj4DKzw1QO9x55hFRDlaZYsLi0MaNLt5T5GQoNr2qHFiUdfw/r37A/h8Syhjn3 8MzYEn32y2TqXGgmkFd60WECTLz5xOAeqdBj8hnKLAZ+9zvB3tgAgY7NxIiqjKTp9G VE2SFe4I3U5bEluW0192FPPhbPrEob8C0ReK+5xwEGaWH+/XwDvUt63aQfbo05yc4o +RYtPr3ZUEkYpBBHf1cwA/SEfbhb+TzzwQKizsYlydqULYUI+px4PQaRVOWSlNmXer OeC2hQA7WZZkQ== Received: from phl-compute-07.internal (phl-compute-07.internal [10.202.2.47]) by mailfauth.ams.internal (Postfix) with ESMTP id 8C4B5198003A; Tue, 10 Nov 2026 07:11:46 -0500 (EST) Received: from phl-frontend-04 ([10.202.2.163]) by phl-compute-07.internal (MEProxy); Tue, 10 Nov 2026 07:11:49 -0500 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: dmFkZTGefbfqVFzQoxpaOb35aOaJJYZFYQvPzGDPo0Iw8/s+5tsv/j0Eaozcf4zKLCSuJk EX6o3FPlxI7euVfy5GZ4yBQeNhray/Eagm6hy/bLiFn43dNlHuG6U9X5dqkW5TdvSDl32E MCiAOECHe557g5jlRnWXG30eabfT2U2GrXuAzLGAvzjETk7rT6T7fRbCYmvUsujMizr16N 71b/VfcY866hCn1NdGBDFB4a8VT++nHkgz2epE5PTIzhAMLSn/jhJLyr1q08Hn0UXkqfDU 5jaBjS4I9mhYqRmUMVG2ZlOyeiZTITO2/kszXi+dWRQZvoFzIn/DouFW5VGKjOJRYrpqRE oWLEZdmA0aiXFnjCrxF4Uk38siGVsWyDPDkHmXGAFAPjxUzKmVw7g9/gAo+OOYyKNiKeY7 VzLvd+Er+ab5ilp3oMLATULyKQyFyPdkSUC0fJy5L6Jhgvo6sJ68OvTbdbRnP2z0UtH8Sy 5n05ryyntrgR8Del3oW+GfLhr4P+CHNI5EzBbbxFth4QRTwBUjPnSIcQqFtG7GSnZNPkcN zxnlOAclNPbLyRXLZP8jqH5iCsBssbIAowSvIJOPmV5sBNlX4uH7jJs7XZ+GK1d/3M1yd4 I8IfqkZu8ig+R1AgkNss5B6cYCw2eOEB6vc/TtNu7oNJNuVfHPEOkerf9p7A X-ME-Proxy: Feedback-ID: i10464835:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Tue, 10 Nov 2026 07:11:45 -0500 (EST) Date: Tue, 10 Nov 2026 12:11:44 +0000 From: Kiryl Shutsemau To: Sasha Levin Cc: akpm@linux-foundation.org, david@kernel.org, muchun.song@linux.dev, osalvador@suse.de, peterz@infradead.org, fvdl@google.com, willy@infradead.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, corbet@lwn.net, skhan@linuxfoundation.org, rdunlap@infradead.org, stable@vger.kernel.org Subject: Re: FAILED: patch "[PATCH] mm/hugetlb_vmemmap: map the shared tail page writable" failed to apply to 6.18-stable tree Message-ID: References: <20261109200434-failed-6.18-0120a603afad@kernel.org> X-Mailing-List: stable@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: <20261109200434-failed-6.18-0120a603afad@kernel.org> On Mon, Nov 09, 2026 at 08:04:34PM -0500, Sasha Levin wrote: > The patch below does not apply to the 6.18-stable tree. It is not needed for 6.18. The bug came with 32c440d67e6c ("mm: drop fake head checks"), which 6.18 does not have. But 6.18.y has its sibling, 01b1d0ffb6f7 ("hugetlb: remove VMEMMAP_SYNCHRONIZE_RCU"), picked up in 6.18.51 as a Stable-dep-of 6e25c6a9c7ef ("mm/hugetlb_vmemmap: fix __hugetlb_vmemmap_optimize_folios()"). It is only correct once fake heads are gone. 6.18 still has them, and page_ref_add_unless() still relies on the synchronize_rcu() it removed, see bd225530a4c7 ("mm/hugetlb_vmemmap: fix race with speculative PFN walkers"). So the race bd225530a4c7 fixed is back in 6.18.y: compaction takes a speculative reference on a PFN, passes page_count_writable() before HVO remaps the tail vmemmap read-only, does its cmpxchg after the remap and oopses. Please revert dba93b8cceb0 from 6.18.y. It reverts cleanly, and 6e25c6a9c7ef applies to 6.18 without it. -- Kiryl Shutsemau / Kirill A. Shutemov