From patchwork Wed May 30 16:00:08 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tetsuo Handa X-Patchwork-Id: 10439321 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id D6CD860327 for ; Wed, 30 May 2018 16:01:30 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C784F2917D for ; Wed, 30 May 2018 16:01:30 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id C5D0129183; Wed, 30 May 2018 16:01:30 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00, MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 72FFC290B5 for ; Wed, 30 May 2018 16:01:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753330AbeE3QBO (ORCPT ); Wed, 30 May 2018 12:01:14 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:23683 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753605AbeE3QBN (ORCPT ); Wed, 30 May 2018 12:01:13 -0400 Received: from fsav403.sakura.ne.jp (fsav403.sakura.ne.jp [133.242.250.102]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id w4UG0JnT064793; Thu, 31 May 2018 01:00:19 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav403.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav403.sakura.ne.jp); Thu, 31 May 2018 01:00:19 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav403.sakura.ne.jp) Received: from [192.168.1.8] (softbank126074194044.bbtec.net [126.74.194.44]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id w4UG0Ats064729 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Thu, 31 May 2018 01:00:19 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) From: Tetsuo Handa Subject: Re: general protection fault in wb_workfn (2) To: Jan Kara Cc: syzbot , syzkaller-bugs@googlegroups.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, axboe@kernel.dk, tj@kernel.org, david@fromorbit.com, linux-block@vger.kernel.org References: <000000000000cbd959056d1851ca@google.com> <0c7c5dea-7312-8a59-9d1b-5467f69719bf@I-love.SAKURA.ne.jp> <20180528133503.awomzj6djozbo5bv@quack2.suse.cz> Message-ID: <2dda7a11-3f6b-bdba-a68a-7c0694806cc4@I-love.SAKURA.ne.jp> Date: Thu, 31 May 2018 01:00:08 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20180528133503.awomzj6djozbo5bv@quack2.suse.cz> Content-Language: en-US Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP So, we have no idea what is happening... Then, what about starting from temporary debug printk() patch shown below? >From 4f70f72ad3c9ae6ce1678024ef740aca4958e5b0 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Wed, 30 May 2018 09:57:10 +0900 Subject: [PATCH] bdi: Add temporary config for debugging wb_workfn() versus bdi_unregister() race bug. syzbot is hitting NULL pointer dereference at wb_workfn() [1]. But due to limitations that syzbot cannot find reproducer for this bug (frequency is once or twice per a day) nor we can't capture vmcore in the environment which syzbot is using, for now we need to rely on printk() debugging. [1] https://syzkaller.appspot.com/bug?id=e0818ccb7e46190b3f1038b0c794299208ed4206 Signed-off-by: Tetsuo Handa --- block/Kconfig | 7 +++++++ fs/fs-writeback.c | 31 +++++++++++++++++++++++++++++++ 2 files changed, 38 insertions(+) diff --git a/block/Kconfig b/block/Kconfig index 28ec557..fbce13e 100644 --- a/block/Kconfig +++ b/block/Kconfig @@ -139,6 +139,13 @@ config BLK_CMDLINE_PARSER See Documentation/block/cmdline-partition.txt for more information. +config BLK_DEBUG_WB_WORKFN_RACE + bool "Dump upon hitting wb_workfn() versus bdi_unregister() race bug." + default n + ---help--- + This is a temporary option used for obtaining information for + specific bug. This option will be removed after the bug is fixed. + config BLK_WBT bool "Enable support for block device writeback throttling" default n diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 471d863..b4dd078 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -1934,6 +1934,37 @@ void wb_workfn(struct work_struct *work) struct bdi_writeback, dwork); long pages_written; +#ifdef CONFIG_BLK_DEBUG_WB_WORKFN_RACE + if (!wb->bdi->dev) { + pr_warn("WARNING: %s: device is NULL\n", __func__); + pr_warn("wb->state=%lx\n", wb->state); + pr_warn("list_empty(&wb->work_list)=%u\n", + list_empty(&wb->work_list)); + if (!wb->bdi) + pr_warn("wb->bdi == NULL\n"); + else { + pr_warn("list_empty(&wb->bdi->bdi_list)=%u\n", + list_empty(&wb->bdi->bdi_list)); + pr_warn("wb->bdi->wb.state=%lx\n", wb->bdi->wb.state); + } + if (!wb->congested) + pr_warn("wb->congested == NULL\n"); +#ifdef CONFIG_CGROUP_WRITEBACK + else if (!wb->congested->__bdi) + pr_warn("wb->congested->__bdi == NULL\n"); + else { + pr_warn("(wb->congested->__bdi == wb->bdi)=%u\n", + wb->congested->__bdi == wb->bdi); + pr_warn("list_empty(&wb->congested->__bdi->bdi_list)=%u\n", + list_empty(&wb->congested->__bdi->bdi_list)); + pr_warn("wb->congested->__bdi->wb.state=%lx\n", + wb->congested->__bdi->wb.state); + } +#endif + /* Will halt shortly due to NULL pointer dereference... */ + } +#endif + set_worker_desc("flush-%s", dev_name(wb->bdi->dev)); current->flags |= PF_SWAPWRITE;