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 X-Spam-Level: X-Spam-Status: No, score=-15.7 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,URIBL_BLOCKED autolearn=unavailable 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 7EFDDC433DB for ; Fri, 5 Feb 2021 02:33:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 584F164FA7 for ; Fri, 5 Feb 2021 02:33:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230249AbhBECdl (ORCPT ); Thu, 4 Feb 2021 21:33:41 -0500 Received: from mail.kernel.org ([198.145.29.99]:46020 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230224AbhBECdf (ORCPT ); Thu, 4 Feb 2021 21:33:35 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2F55964FB8; Fri, 5 Feb 2021 02:32:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1612492353; bh=Ej+wJlFyaECsFAWWUxNTxpzUQNone8iCdAcIp4GZvpQ=; h=Date:From:To:Subject:In-Reply-To:From; b=lI5V8mJqUYZZpQ9q2kiiElRnSPGzLp01BujQRXt3DBAOl+/bJipzo1wGrpTNIjPdS ZZXSE7hjXHa6MgQ35CE4mtOFSvpf6XPi3n124i31oMtV8IX8UHCLnPKA9FJY/Nk3Kd mD3bp1yRSd2ccxzHWFm/DRWz2tVWecsWvRJgisFw= Date: Thu, 04 Feb 2021 18:32:31 -0800 From: Andrew Morton To: aarcange@redhat.com, akpm@linux-foundation.org, hughd@google.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, sergey.senozhatsky.work@gmail.com, stable@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 09/18] mm: thp: fix MADV_REMOVE deadlock on shmem THP Message-ID: <20210205023231.ne7UDbPxT%akpm@linux-foundation.org> In-Reply-To: <20210204183135.e123f0d6027529f2cf500cf2@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Hugh Dickins Subject: mm: thp: fix MADV_REMOVE deadlock on shmem THP Sergey reported deadlock between kswapd correctly doing its usual lock_page(page) followed by down_read(page->mapping->i_mmap_rwsem), and madvise(MADV_REMOVE) on an madvise(MADV_HUGEPAGE) area doing down_write(page->mapping->i_mmap_rwsem) followed by lock_page(page). This happened when shmem_fallocate(punch hole)'s unmap_mapping_range() reaches zap_pmd_range()'s call to __split_huge_pmd(). The same deadlock could occur when partially truncating a mapped huge tmpfs file, or using fallocate(FALLOC_FL_PUNCH_HOLE) on it. __split_huge_pmd()'s page lock was added in 5.8, to make sure that any concurrent use of reuse_swap_page() (holding page lock) could not catch the anon THP's mapcounts and swapcounts while they were being split. Fortunately, reuse_swap_page() is never applied to a shmem or file THP (not even by khugepaged, which checks PageSwapCache before calling), and anonymous THPs are never created in shmem or file areas: so that __split_huge_pmd()'s page lock can only be necessary for anonymous THPs, on which there is no risk of deadlock with i_mmap_rwsem. Link: https://lkml.kernel.org/r/alpine.LSU.2.11.2101161409470.2022@eggly.anvils Fixes: c444eb564fb1 ("mm: thp: make the THP mapcount atomic against __split_huge_pmd_locked()") Signed-off-by: Hugh Dickins Reported-by: Sergey Senozhatsky Reviewed-by: Andrea Arcangeli Cc: Signed-off-by: Andrew Morton --- mm/huge_memory.c | 37 +++++++++++++++++++++++-------------- 1 file changed, 23 insertions(+), 14 deletions(-) --- a/mm/huge_memory.c~mm-thp-fix-madv_remove-deadlock-on-shmem-thp +++ a/mm/huge_memory.c @@ -2202,7 +2202,7 @@ void __split_huge_pmd(struct vm_area_str { spinlock_t *ptl; struct mmu_notifier_range range; - bool was_locked = false; + bool do_unlock_page = false; pmd_t _pmd; mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm, @@ -2218,7 +2218,6 @@ void __split_huge_pmd(struct vm_area_str VM_BUG_ON(freeze && !page); if (page) { VM_WARN_ON_ONCE(!PageLocked(page)); - was_locked = true; if (page != pmd_page(*pmd)) goto out; } @@ -2227,19 +2226,29 @@ repeat: if (pmd_trans_huge(*pmd)) { if (!page) { page = pmd_page(*pmd); - if (unlikely(!trylock_page(page))) { - get_page(page); - _pmd = *pmd; - spin_unlock(ptl); - lock_page(page); - spin_lock(ptl); - if (unlikely(!pmd_same(*pmd, _pmd))) { - unlock_page(page); + /* + * An anonymous page must be locked, to ensure that a + * concurrent reuse_swap_page() sees stable mapcount; + * but reuse_swap_page() is not used on shmem or file, + * and page lock must not be taken when zap_pmd_range() + * calls __split_huge_pmd() while i_mmap_lock is held. + */ + if (PageAnon(page)) { + if (unlikely(!trylock_page(page))) { + get_page(page); + _pmd = *pmd; + spin_unlock(ptl); + lock_page(page); + spin_lock(ptl); + if (unlikely(!pmd_same(*pmd, _pmd))) { + unlock_page(page); + put_page(page); + page = NULL; + goto repeat; + } put_page(page); - page = NULL; - goto repeat; } - put_page(page); + do_unlock_page = true; } } if (PageMlocked(page)) @@ -2249,7 +2258,7 @@ repeat: __split_huge_pmd_locked(vma, pmd, range.start, freeze); out: spin_unlock(ptl); - if (!was_locked && page) + if (do_unlock_page) unlock_page(page); /* * No need to double call mmu_notifier->invalidate_range() callback. _