From patchwork Fri Jun 25 01:39:26 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 467400 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C78D6C49EAF for ; Fri, 25 Jun 2021 01:39:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B58326044F for ; Fri, 25 Jun 2021 01:39:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232917AbhFYBlr (ORCPT ); Thu, 24 Jun 2021 21:41:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:60596 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233027AbhFYBlr (ORCPT ); Thu, 24 Jun 2021 21:41:47 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 3607B60232; Fri, 25 Jun 2021 01:39:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1624585167; bh=4Phypuv2rU6Ab0eZiywnXZFZ3Vmw48lZy36NgYBtlD0=; h=Date:From:To:Subject:In-Reply-To:From; b=v2XhV9y4qjkCAlefedB1QitxJNJRcA0A7KL8c8EyZctrmpSXS9F13LCAWlaGIjUPw KVFcLmvIReDxPXfhlipeg0CwpsA38lpHGD9Wy0UAx7eC73Xmee+U9Jku5ds5KCHpyn cKMKJDZMV0yfjRdl5UKYlUHpfdvjy6CvM+sJJ5n4= Date: Thu, 24 Jun 2021 18:39:26 -0700 From: Andrew Morton To: akpm@linux-foundation.org, apopple@nvidia.com, hughd@google.com, kirill.shutemov@linux.intel.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, peterx@redhat.com, rcampbell@nvidia.com, shy828301@gmail.com, stable@vger.kernel.org, torvalds@linux-foundation.org, wangyugui@e16-tech.com, will@kernel.org, willy@infradead.org, ziy@nvidia.com Subject: [patch 09/24] mm/thp: fix page_vma_mapped_walk() if THP mapped by ptes Message-ID: <20210625013926.7ZTZ9B0S5%akpm@linux-foundation.org> In-Reply-To: <20210624183838.ac3161ca4a43989665ac8b2f@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Hugh Dickins Subject: mm/thp: fix page_vma_mapped_walk() if THP mapped by ptes Running certain tests with a DEBUG_VM kernel would crash within hours, on the total_mapcount BUG() in split_huge_page_to_list(), while trying to free up some memory by punching a hole in a shmem huge page: split's try_to_unmap() was unable to find all the mappings of the page (which, on a !DEBUG_VM kernel, would then keep the huge page pinned in memory). Crash dumps showed two tail pages of a shmem huge page remained mapped by pte: ptes in a non-huge-aligned vma of a gVisor process, at the end of a long unmapped range; and no page table had yet been allocated for the head of the huge page to be mapped into. Although designed to handle these odd misaligned huge-page-mapped-by-pte cases, page_vma_mapped_walk() falls short by returning false prematurely when !pmd_present or !pud_present or !p4d_present or !pgd_present: there are cases when a huge page may span the boundary, with ptes present in the next. Restructure page_vma_mapped_walk() as a loop to continue in these cases, while keeping its layout much as before. Add a step_forward() helper to advance pvmw->address across those boundaries: originally I tried to use mm's standard p?d_addr_end() macros, but hit the same crash 512 times less often: because of the way redundant levels are folded together, but folded differently in different configurations, it was just too difficult to use them correctly; and step_forward() is simpler anyway. Link: https://lkml.kernel.org/r/fedb8632-1798-de42-f39e-873551d5bc81@google.com Fixes: ace71a19cec5 ("mm: introduce page_vma_mapped_walk()") Signed-off-by: Hugh Dickins Acked-by: Kirill A. Shutemov Cc: Alistair Popple Cc: Matthew Wilcox Cc: Peter Xu Cc: Ralph Campbell Cc: Wang Yugui Cc: Will Deacon Cc: Yang Shi Cc: Zi Yan Cc: Signed-off-by: Andrew Morton --- mm/page_vma_mapped.c | 34 +++++++++++++++++++++++++--------- 1 file changed, 25 insertions(+), 9 deletions(-) --- a/mm/page_vma_mapped.c~mm-thp-fix-page_vma_mapped_walk-if-thp-mapped-by-ptes +++ a/mm/page_vma_mapped.c @@ -116,6 +116,13 @@ static bool check_pte(struct page_vma_ma return pfn_is_match(pvmw->page, pfn); } +static void step_forward(struct page_vma_mapped_walk *pvmw, unsigned long size) +{ + pvmw->address = (pvmw->address + size) & ~(size - 1); + if (!pvmw->address) + pvmw->address = ULONG_MAX; +} + /** * page_vma_mapped_walk - check if @pvmw->page is mapped in @pvmw->vma at * @pvmw->address @@ -183,16 +190,22 @@ bool page_vma_mapped_walk(struct page_vm if (pvmw->pte) goto next_pte; restart: - { + do { pgd = pgd_offset(mm, pvmw->address); - if (!pgd_present(*pgd)) - return false; + if (!pgd_present(*pgd)) { + step_forward(pvmw, PGDIR_SIZE); + continue; + } p4d = p4d_offset(pgd, pvmw->address); - if (!p4d_present(*p4d)) - return false; + if (!p4d_present(*p4d)) { + step_forward(pvmw, P4D_SIZE); + continue; + } pud = pud_offset(p4d, pvmw->address); - if (!pud_present(*pud)) - return false; + if (!pud_present(*pud)) { + step_forward(pvmw, PUD_SIZE); + continue; + } pvmw->pmd = pmd_offset(pud, pvmw->address); /* @@ -239,7 +252,8 @@ restart: spin_unlock(ptl); } - return false; + step_forward(pvmw, PMD_SIZE); + continue; } if (!map_pte(pvmw)) goto next_pte; @@ -269,7 +283,9 @@ next_pte: spin_lock(pvmw->ptl); } goto this_pte; - } + } while (pvmw->address < end); + + return false; } /**