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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8B3EAC433EF for ; Tue, 28 Jun 2022 13:31:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345841AbiF1NbU (ORCPT ); Tue, 28 Jun 2022 09:31:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57782 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240510AbiF1NaI (ORCPT ); Tue, 28 Jun 2022 09:30:08 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0AA7E2C113 for ; Tue, 28 Jun 2022 06:28:48 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.55]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4LXQNv5sP8zkWYD; Tue, 28 Jun 2022 21:26:55 +0800 (CST) Received: from huawei.com (10.175.124.27) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Tue, 28 Jun 2022 21:28:45 +0800 From: Miaohe Lin To: CC: , , , , , , Subject: [PATCH v2 15/16] mm/huge_memory: comment the subtly logic in __split_huge_pmd Date: Tue, 28 Jun 2022 21:28:34 +0800 Message-ID: <20220628132835.8925-16-linmiaohe@huawei.com> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20220628132835.8925-1-linmiaohe@huawei.com> References: <20220628132835.8925-1-linmiaohe@huawei.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Content-Type: text/plain; charset=US-ASCII X-Originating-IP: [10.175.124.27] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It's dangerous and wrong to call page_folio(pmd_page(*pmd)) when pmd isn't present. But the caller guarantees pmd is present when folio is set. So we should be safe here. Add comment to make it clear. Signed-off-by: Miaohe Lin --- mm/huge_memory.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 36570d800f21..1d32349a95f4 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2335,6 +2335,10 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) || is_pmd_migration_entry(*pmd)) { + /* + * It's safe to call pmd_page when folio is set because it's + * guaranteed that pmd is present. + */ if (folio && folio != page_folio(pmd_page(*pmd))) goto out; __split_huge_pmd_locked(vma, pmd, range.start, freeze); -- 2.23.0