From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 6A603CFC295 for ; Fri, 21 Nov 2025 17:09:27 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9A1106B002B; Fri, 21 Nov 2025 12:09:26 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 978F86B002C; Fri, 21 Nov 2025 12:09:26 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8B5A26B002D; Fri, 21 Nov 2025 12:09:26 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 790766B002B for ; Fri, 21 Nov 2025 12:09:26 -0500 (EST) Received: from smtpin08.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id E7D0BBA743 for ; Fri, 21 Nov 2025 17:09:25 +0000 (UTC) X-FDA: 84135250290.08.43A5BB9 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf12.hostedemail.com (Postfix) with ESMTP id 2A9484001F for ; Fri, 21 Nov 2025 17:09:23 +0000 (UTC) Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=ODepD5DC; spf=pass (imf12.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1763744964; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=fwAcWMplDqNL4zpiZZqIc8wNhnOOOAO06Vg7iEtF0gU=; b=zemOH5dSKcnLJGTvswRhFSUgJzQNp6PazgzDszIOR751xD7i3hRlro7Doidg83eX18GEzq ruDC1G7zVfNmP1Tw2FYENkzSFT5iqcbEgsqn1yCI8N8HQePaj/BaZ5HbkiG5G4v9Ozar/0 qW3w1w1dm3Fl0V4ZTS1GRclxRkEdi7s= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=ODepD5DC; spf=pass (imf12.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1763744964; a=rsa-sha256; cv=none; b=8QBQwvyKn/4SLI4shIILSV2gKN+rvWoBEfu+y/7+zzDKg5rAb9nTEOXQjZIHdvF/Sk8103 UMNtur53Lt/AG+mEfEN3DHzO6+X1BieLsTJuF3W3IJHPAVeS9WM3Q/g83Rx8PBoBqlmgUF KBq2qEXdvLxkiU+ZIA1yGyDssed1Rl8= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id C31EF4063A; Fri, 21 Nov 2025 17:09:22 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8246BC4CEF1; Fri, 21 Nov 2025 17:09:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763744962; bh=wbtbUmI+JYBD2T+C4kTcqxXZdRf5waIyL5iLdAIi17I=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ODepD5DCIv5oRt2HVCh5GwfvCEkSdBsa9KK7pBqILQdKuNbSqMeSJtIi/PaTKYmVe KJ45zZjgb/1Dkmu/Xu3M+lQ5kjQpOGKMX7opaOYWO4HABkS11L2YMUS5sxtE4Hx2R1 q1MVVEqCmnHhyOCHzhkTpB9OSdPvu9jEb62+5sLEu5lO7yy4K1nuRg5KfWqL+Mpa2p WO8uifpeuNXi5CJMvIB2upXpp1NPov2CwTCmyvBjnu1qxLyGtmHwBud8qDK4snUE9t dZreWNmiDJzdonAjkfsywN9wmVbBsav6MlxrmLqAvVbDm17sglU0PNsu0bGy6NdR8C ZSHfquPmOps3g== Message-ID: Date: Fri, 21 Nov 2025 18:09:16 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 1/3] mm/huge_memory: prevent NULL pointer dereference in try_folio_split_to_order() To: Zi Yan Cc: Lorenzo Stoakes , Andrew Morton , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Miaohe Lin , Naoya Horiguchi , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20251120035953.1115736-1-ziy@nvidia.com> <20251120035953.1115736-2-ziy@nvidia.com> <875584d7-5a68-4f7a-8549-2a9cd6c7f9d8@kernel.org> <73075A18-3C07-46F5-B8C8-9018D2CD22DE@nvidia.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <73075A18-3C07-46F5-B8C8-9018D2CD22DE@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 2A9484001F X-Stat-Signature: aamt85ezen75jehyjhome8ygqc5sfhnj X-Rspam-User: X-HE-Tag: 1763744963-774893 X-HE-Meta: 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 B6dpUIBW Elc0gM2vUiV7htolzwTHeTltDAuIZYpoP9jgTXt8UX7LINJ/szC2S8AwRLQhs31UCfVWQ2fYYYhdy3EFtF9Gu/WbZAM9f2T0MajsxX8liMAY9iMy52Dd89rAjCHxsNjqWNPT7oDBODWOd3mnnkBxMqQb0hFuUato9LARTI2YrNj6sN6w24huY1KeuoSd9JIWfYI4pyvsOMbUqmT4Yn8IV3TN/k5MFrs1yQENpx32+uICAYMRN9bxBJAGy2K2aK8JCJI4INvwYM9cOnfiOfWrc1UeYMng3XBwm+u+V9uKULBZ2ACQRPD6VTYouIBiVC+xqaU1z2OctAlACyX1X7Jlfm58tv63fj4QIopqkt6TTHnNNtuIrsm16EgAqgneTn9hKxpLz 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: >> >> BTW, I wonder if the is_huge_zero_folio() check should go into folio_split_supported() and just return in -EINVAL. (we shouldn't really trigger that). Similarly we could add a hugetlb sanity check. > > Yeah, is_huge_zero_folio() should return -EINVAL not -EBUSY, except > the case the split happens before a process writes 0 to a zero large folio > and gets a new writable large folio, in which we can kinda say it looks like > -EBUSY. But it is still a stretch. I see what you mean, but I think this has less to do with actual races. SO yeah, -EINVAL is likely the tight thing. > > Ack on adding hugetlb sanity check. > > OK, just to reiterate my above idea on renaming folio_split_supported(). > Are you OK with renaming it to folio_split_check(), so that returning -EBUSY > and -EINVAL looks more reasonable? The benefit is that we no longer need > to worry about we need to always do folio->mapping check before > folio_split_supported(). (In addition, I would rename can_split_folio() > to folio_split_refcount_check() for clarification) I guess having some function that tells you "I performed all checks I could without taking locks/references (like anon_vma) and starting with the real magic" is what you have in mind. For these we don't have to prefix with "folio_split" if it sounds weird. folio_check_splittable() ? Regarding can_split_folio(), I was wondering whether we can just get rid of it and use folio_expect_ref_count() instead? For the two callers that need extra_pins, we could just have something simple helper in huge_memory.c like /* Number of folio references from the pagecache or the swapcache. */ unsigned int folio_cache_references(const struct folio *folio) { if (folio_test_anon(folio) && !folio_test_swapcache(folio)) return 0; return folio_nr_pages(folio); } -- Cheers David