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=-8.6 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_PASS,USER_IN_DEF_DKIM_WL 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 0B086C282E1 for ; Tue, 23 Apr 2019 17:16:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CC4DC21738 for ; Tue, 23 Apr 2019 17:16:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="Y5GWoYoc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728894AbfDWRQX (ORCPT ); Tue, 23 Apr 2019 13:16:23 -0400 Received: from mail-yw1-f68.google.com ([209.85.161.68]:38040 "EHLO mail-yw1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727656AbfDWRQX (ORCPT ); Tue, 23 Apr 2019 13:16:23 -0400 Received: by mail-yw1-f68.google.com with SMTP id i66so1873264ywe.5 for ; Tue, 23 Apr 2019 10:16:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=g3T77yqZJMe1qswiJgxzxS6pAsqLXpPMxdOnm+lBM4E=; b=Y5GWoYocQ4eb5zga5g5j9h5RECpENQqtMthIB5pedH+P/CPcipOYk4+SrQ8EAhoP1I c4c22LQvPk05ewHoupqa+wvt7dj35Nl/2GXgEnvKaOWrzuz8kUaZY1Y6EpUJhg3lL3hu 1jZoEzLK6jXgDExOEqFJQcQ9uQW8Ge4dWFHpw2x/fMy/QSdgvcn8NDsuwN43xf5qXKPe 7HO8yfcGrt8R9rJ4hmjmf4lahd7N7+CoD42CGVfwz+MVPTkFFb5Hn7a/5JeE+Z2uuxmd NelYHDdN2PGKJv7DyPbTGqNBqIFt/pei3TOEGY1CBeSBH8cAuQgGWPAyv1y/eTplVbVh Y+Eg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=g3T77yqZJMe1qswiJgxzxS6pAsqLXpPMxdOnm+lBM4E=; b=afEV0eQ0n89RASCbkjSYWAyzOScMpJkVa3dn/erXop5EoXCsXDFbrOVHUdr8daxuZD NfsATUuOxOiAAx+vePcGq4Q4glavtkTmSFQYlvXJCjhEqcL2mc8k+aiy8EgV30BPVmZn Fx1GVzP//5KEvjf+3fLF3ge1iR0aL+Daf3JfXQhSGvc5rXyEh8+Hwi33nsA6cM4Y+Zcz Rc8EAdIT0+oznLgK6XK+QZrieuJH18fQeu+kbSqWjcBZvSg4aLBikN9Q30pr6O638NGi LtgAq33TMaMLkJrS6eJu0LWYtFaet5JfFQ97OJhZ3dm+4M5pid8AGxgXiceBev3dNQ/q JTfQ== X-Gm-Message-State: APjAAAXYavIbMcpjhsyBg7xfS3tJ6/3bt+REmYv6MmwErWW7EFxIJ48w tdBK5ihpjEkbx/qJ8MYVERYp34lvYAejw6x+rQtfng== X-Google-Smtp-Source: APXvYqxx3W4CgkV6x2r0WAmwpahB8VurbOMz3+wQ0ZYRON8CtzQn5jiRcQGe7KgKK9gYvc+quqqsQfNkFASNLHpDleg= X-Received: by 2002:a81:30d8:: with SMTP id w207mr12068553yww.362.1556039781035; Tue, 23 Apr 2019 10:16:21 -0700 (PDT) MIME-Version: 1.0 References: <20190423163021.GA185682@google.com> <20190423170127.GA26119@magnolia> In-Reply-To: <20190423170127.GA26119@magnolia> From: Guenter Roeck Date: Tue, 23 Apr 2019 10:16:09 -0700 Message-ID: Subject: Re: 5a9d929d6e13 ("iomap: report collisions between directio and buffered writes to userspace") To: "Darrick J. Wong" Cc: Zubin Mithra , "# v4 . 10+" , Greg Kroah-Hartman , Guenter Roeck , bo.li.liu@oracle.com, viro@zeniv.linux.org.uk, linux-ext4 Content-Type: text/plain; charset="UTF-8" Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Tue, Apr 23, 2019 at 10:01 AM Darrick J. Wong wrote: > > On Tue, Apr 23, 2019 at 09:30:22AM -0700, Zubin Mithra wrote: > > Hello, > > > > Syzkaller has triggered a kernel WARNING with the following stacktrace when fuzzing a 4.14 kernel. > > > > Call Trace: > > __dump_stack lib/dump_stack.c:17 [inline] > > dump_stack+0xb7/0x107 lib/dump_stack.c:53 > > panic+0x1c9/0x3ae kernel/panic.c:181 > > __warn+0x160/0x1a8 kernel/panic.c:543 > > report_bug+0x123/0x18b lib/bug.c:186 > > fixup_bug+0x3e/0x77 arch/x86/kernel/traps.c:177 > > do_error_trap+0xdd/0x1e6 arch/x86/kernel/traps.c:295 > > invalid_op+0x1b/0x40 arch/x86/entry/entry_64.S:944 > > do_blockdev_direct_IO+0x1b08/0x1b95 fs/direct-io.c:1373 > > ext4_direct_IO_write fs/ext4/inode.c:3696 [inline] > > ext4_direct_IO+0x8de/0xdad fs/ext4/inode.c:3826 > > generic_file_direct_write+0x223/0x36b mm/filemap.c:2927 > > __generic_file_write_iter+0x12f/0x2f8 mm/filemap.c:3106 > > ext4_file_write_iter+0x97d/0xade fs/ext4/file.c:264 > > call_write_iter include/linux/fs.h:1782 [inline] > > do_iter_readv_writev+0x1e4/0x27c fs/read_write.c:678 > > do_iter_write+0x136/0x18f fs/read_write.c:957 > > vfs_iter_write+0x81/0x98 fs/read_write.c:970 > > iter_file_splice_write+0x4dc/0x7a6 fs/splice.c:749 > > do_splice_from fs/splice.c:851 [inline] > > direct_splice_actor+0x11e/0x129 fs/splice.c:1018 > > splice_direct_to_actor+0x342/0x5b0 fs/splice.c:973 > > do_splice_direct+0x180/0x1ff fs/splice.c:1061 > > do_sendfile+0x3e6/0x61c fs/read_write.c:1438 > > SYSC_sendfile64 fs/read_write.c:1499 [inline] > > SyS_sendfile64+0xe9/0x128 fs/read_write.c:1485 > > do_syscall_64+0x203/0x241 arch/x86/entry/common.c:290 > > entry_SYSCALL_64_after_hwframe+0x42/0xb7 > > > > Could the following patch be applied in order to v4.14.y(The patch is present in v4.19.y)? > > 5a9d929d6e13 ("iomap: report collisions between directio and buffered writes to userspace") > > That patch only teaches the kernel to emit warnings in dmesg when > programs mix directio and buffered writes. It doesn't fix any buggy > directio usage. Someone on the ext4 list [cc'd] might know more about > this. > Not sure I understand. Is your argument that systems configured to panic on warnings should indeed panic if the situation is encountered, ie that the backtrace and potential panic is warranted ? Isn't this a potential DOS problem if the situation can be triggered from userspace on such systems ? Thanks, Guenter > --D > > > > > Tests run: > > - Chrome OS tryjobs > > - Syzkaller reproducer > > > > > > Thanks, > > - Zubin