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=-6.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 1A9A1C433DF for ; Fri, 21 Aug 2020 00:42:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E4F502087D for ; Fri, 21 Aug 2020 00:42:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597970527; bh=+WvEgrYIHkkeUnjluxstf/SQ+TuZELLSwpag0oqeBFw=; h=Date:From:To:Subject:In-Reply-To:Reply-To:List-ID:From; b=WwCnjPkZcs09x8fjaQQUTozqQRcrNEWVHTCI+C6Hd1vXHBb2vqDvK6dVdZzGc8vOU N0FJLJEQ5eAtZIVj7Tu3pdh+yxJsyES633vdl9ba6to/pYe6PXOYEadsuliBt2kPoq 9Nz4Ahwn6PJj1XUYoQHpwq6bSnXjRTLikq3jQDGU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726956AbgHUAmG (ORCPT ); Thu, 20 Aug 2020 20:42:06 -0400 Received: from mail.kernel.org ([198.145.29.99]:35258 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726918AbgHUAmD (ORCPT ); Thu, 20 Aug 2020 20:42:03 -0400 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8F296207DF; Fri, 21 Aug 2020 00:42:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597970523; bh=+WvEgrYIHkkeUnjluxstf/SQ+TuZELLSwpag0oqeBFw=; h=Date:From:To:Subject:In-Reply-To:From; b=nalZHLdnZOpXk7HvdakXtnze4hoQHp4fETpt6OUptZ6lvumiyccmbVnlDXNemqxuQ GvwpfQaBLEL9SdRAiwa/nziUkElcDJSiGrVleDKdSJ59m6/nC6Uw79nW2kPs/FTztD icKdUuIT4p032cgkDIjWPvrrrAO2y9jxZPFRWhPk= Date: Thu, 20 Aug 2020 17:42:02 -0700 From: Andrew Morton To: aarcange@redhat.com, akpm@linux-foundation.org, edumazet@google.com, hughd@google.com, kirill.shutemov@linux.intel.com, linux-mm@kvack.org, mike.kravetz@oracle.com, mm-commits@vger.kernel.org, shy828301@gmail.com, songliubraving@fb.com, stable@vger.kernel.org, syzkaller@googlegroups.com, torvalds@linux-foundation.org Subject: [patch 03/11] khugepaged: adjust VM_BUG_ON_MM() in __khugepaged_enter() Message-ID: <20200821004202.AP6gJKDLE%akpm@linux-foundation.org> In-Reply-To: <20200820174132.67fd4a7a9359048f807a533b@linux-foundation.org> User-Agent: s-nail v14.8.16 Sender: mm-commits-owner@vger.kernel.org Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Hugh Dickins Subject: khugepaged: adjust VM_BUG_ON_MM() in __khugepaged_enter() syzbot crashes on the VM_BUG_ON_MM(khugepaged_test_exit(mm), mm) in __khugepaged_enter(): yes, when one thread is about to dump core, has set core_state, and is waiting for others, another might do something calling __khugepaged_enter(), which now crashes because I lumped the core_state test (known as "mmget_still_valid") into khugepaged_test_exit(). I still think it's best to lump them together, so just in this exceptional case, check mm->mm_users directly instead of khugepaged_test_exit(). Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008141503370.18085@eggly.anvils Fixes: bbe98f9cadff ("khugepaged: khugepaged_test_exit() check mmget_still_valid()") Signed-off-by: Hugh Dickins Reported-by: syzbot Acked-by: Yang Shi Cc: "Kirill A. Shutemov" Cc: Andrea Arcangeli Cc: Song Liu Cc: Mike Kravetz Cc: Eric Dumazet Cc: [4.8+] Signed-off-by: Andrew Morton --- mm/khugepaged.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/khugepaged.c~khugepaged-adjust-vm_bug_on_mm-in-__khugepaged_enter +++ a/mm/khugepaged.c @@ -466,7 +466,7 @@ int __khugepaged_enter(struct mm_struct return -ENOMEM; /* __khugepaged_exit() must not run from under us */ - VM_BUG_ON_MM(khugepaged_test_exit(mm), mm); + VM_BUG_ON_MM(atomic_read(&mm->mm_users) == 0, mm); if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) { free_mm_slot(mm_slot); return 0; _