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 23F6DC2BB41 for ; Wed, 17 Aug 2022 08:31:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231910AbiHQIbg (ORCPT ); Wed, 17 Aug 2022 04:31:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41732 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229658AbiHQIbd (ORCPT ); Wed, 17 Aug 2022 04:31:33 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B79917D7B6 for ; Wed, 17 Aug 2022 01:31:31 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.54]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4M71R84n7czGpdx; Wed, 17 Aug 2022 16:29:56 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) 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; Wed, 17 Aug 2022 16:31:28 +0800 To: Andrew Morton , , Muchun Song , Linux-MM , linux-kernel From: Miaohe Lin Subject: [bug report] mm/hugetlb: various bugs with avoid_reserve case in alloc_huge_page() Message-ID: Date: Wed, 17 Aug 2022 16:31:28 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) 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 Hi all: When I investigate the mm/hugetlb.c code again, I found there are a few possible issues with avoid_reserve case. (It's really hard to follow the relevant code for me.) Please take a look at the below analysis: 1.avoid_reserve issue with h->resv_huge_pages in alloc_huge_page. Assume: h->free_huge_pages 60 h->resv_huge_pages 30 spool->rsv_hpages 30 When avoid_reserve is true, after alloc_huge_page(), we will have: spool->rsv_hpages 29 /* hugepage_subpool_get_pages decreases it. */ h->free_huge_pages 59 h->resv_huge_pages 30 /* rsv_hpages is used, but *h->resv_huge_pages is not modified accordingly*. */ If the hugetlb page is freed later, we will have: spool->rsv_hpages 30 /* hugepage_subpool_put_pages increases it. */ h->free_huge_pages 60 h->resv_huge_pages 31 /* *increased wrongly* due to hugepage_subpool_put_pages(spool, 1) == 0. */ ^^ 2.avoid_reserve issue with hugetlb rsvd cgroup charge for private mappings in alloc_huge_page. In general, if hugetlb pages are reserved, corresponding rsvd counters are charged in resv_maps for private mappings. Otherwise they're charged in individual hugetlb pages. When alloc_huge_page() is called with avoid_reserve == true, hugetlb_cgroup_charge_cgroup_rsvd() will be called to charge the newly allocated hugetlb page even if there has a reservation for this page in resv_maps. Then vma_commit_reservation() is called to indicate that the reservation is consumed. So the reservation *can not be used, thus leaking* from now on because vma_needs_reservation always return 1 for it. 3.avoid_reserve issue with restore_reserve_on_error There's a assumption in restore_reserve_on_error(): If HPageRestoreReserve is not set, this indicates there is an entry in the reserve map added by alloc_huge_page or HPageRestoreReserve would be set on the page. But this assumption *does not hold for avoid_reserve*. HPageRestoreReserve won't be set even if there is already an entry in the reserve map for avoid_reserve case. So avoid_reserve should be considered in this function, i.e. we need *a reliable way* to determine whether the entry is added by the alloc_huge_page(). Are above issues possible? Or am I miss something? These possible issues seem not easy to fix for me. Any thoughts? Any response would be appreciated! Thanks! Miaohe Lin