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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 A8E16C0044C for ; Wed, 31 Oct 2018 09:56:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 616C6205F4 for ; Wed, 31 Oct 2018 09:56:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 616C6205F4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=I-love.SAKURA.ne.jp Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728029AbeJaSyG (ORCPT ); Wed, 31 Oct 2018 14:54:06 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:59774 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727645AbeJaSyF (ORCPT ); Wed, 31 Oct 2018 14:54:05 -0400 Received: from fsav106.sakura.ne.jp (fsav106.sakura.ne.jp [27.133.134.233]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id w9V9uUup097908; Wed, 31 Oct 2018 18:56:30 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav106.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav106.sakura.ne.jp); Wed, 31 Oct 2018 18:56:30 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav106.sakura.ne.jp) Received: from [192.168.1.8] (softbank060157065137.bbtec.net [60.157.65.137]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id w9V9uOUc097778 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 31 Oct 2018 18:56:30 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Subject: Re: WARNING in kernfs_get To: gregkh@linuxfoundation.org, tj@kernel.org References: <000000000000f921ae05757f567c@google.com> Cc: syzbot , linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com From: Tetsuo Handa Message-ID: Date: Wed, 31 Oct 2018 18:56:23 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <000000000000f921ae05757f567c@google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/09/10 16:31, syzbot wrote: > HEAD commit:    9a5682765a2e Merge branch 'x86-urgent-for-linus' of git://.. > git tree:       upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=1624858e400000 > kernel config:  https://syzkaller.appspot.com/x/.config?x=8f59875069d721b6 > dashboard link: https://syzkaller.appspot.com/bug?extid=3dcb532381f98c86aeb1 > compiler:       gcc (GCC) 8.0.1 20180413 (experimental) > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12657f0a400000 > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=117728ae400000 Here is a simplified reproducer. ---------- #include #include #include #include int main(int argc, char *argv[]) { int i; for (i = 0; i < 16; i++) if (fork() == 0) while (1) { int fd = open("/dev/vhci", O_WRONLY); write(fd, "\xff\x80", 2); close(fd); } while (1) pause(); return 0; } ---------- According to debug printk() patch, atomic_read(&kn->active) == KN_DEACTIVATED_BIAS when we hit WARN_ON(!atomic_read(&kn->count)) at kernfs_get(). Therefore, I guess that the caller is failing to check whether kn is already deactivated (and hence need to recreate a new entry by that name) before reusing existing kn.