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 BB19FC43334 for ; Wed, 22 Jun 2022 17:07:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377122AbiFVRHS (ORCPT ); Wed, 22 Jun 2022 13:07:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42684 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1377037AbiFVRGn (ORCPT ); Wed, 22 Jun 2022 13:06:43 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4EED03F307 for ; Wed, 22 Jun 2022 10:06:37 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.56]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4LSqWk2dxzzkWhM; Thu, 23 Jun 2022 01:05:22 +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; Thu, 23 Jun 2022 01:06:34 +0800 From: Miaohe Lin To: CC: , , , , , Subject: [PATCH 16/16] mm/huge_memory: comment the subtle logic in __split_huge_pmd Date: Thu, 23 Jun 2022 01:06:27 +0800 Message-ID: <20220622170627.19786-17-linmiaohe@huawei.com> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20220622170627.19786-1-linmiaohe@huawei.com> References: <20220622170627.19786-1-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: dggems702-chm.china.huawei.com (10.3.19.179) 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 8bd937cc1f74..b98b97592bd3 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2234,6 +2234,10 @@ 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