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 07D78C5CFC1 for ; Tue, 19 Jun 2018 14:10:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B8AA420883 for ; Tue, 19 Jun 2018 14:10:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B8AA420883 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 S966375AbeFSOKr (ORCPT ); Tue, 19 Jun 2018 10:10:47 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:40883 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755616AbeFSOKo (ORCPT ); Tue, 19 Jun 2018 10:10:44 -0400 Received: from fsav301.sakura.ne.jp (fsav301.sakura.ne.jp [153.120.85.132]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id w5JEAXpo097734; Tue, 19 Jun 2018 23:10:33 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav301.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav301.sakura.ne.jp); Tue, 19 Jun 2018 23:10:33 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav301.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 w5JEAMMv097635 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Tue, 19 Jun 2018 23:10:33 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: INFO: task hung in __get_super To: Dmitry Vyukov Cc: syzbot , syzkaller-bugs , linux-fsdevel , LKML , Al Viro References: <001a113ed5540f411c0568cc8418@google.com> From: Tetsuo Handa Message-ID: <9d0092e6-142a-7168-7b3c-084faa9268d5@i-love.sakura.ne.jp> Date: Tue, 19 Jun 2018 23:10:17 +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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/06/19 20:53, Dmitry Vyukov wrote: > On Tue, Jun 19, 2018 at 1:44 PM, Tetsuo Handa > wrote: >> This bug report is getting no feedback, but I guess that this bug is in >> block or mm or locking layer rather than fs layer. >> >> NMI backtrace for this bug tends to report that sb_bread() from fill_super() >> from mount_bdev() is stalling is the cause of keep holding s_umount_key for >> more than 120 seconds. What is strange is that NMI backtrace for this bug tends >> to point at rcu_read_lock()/pagecache_get_page()/radix_tree_deref_slot()/ >> rcu_read_unlock() which is expected not to stall. >> >> Since CONFIG_RCU_CPU_STALL_TIMEOUT is set to 120 (and actually +5 due to >> CONFIG_PROVE_RCU=y) which is longer than CONFIG_DEFAULT_HUNG_TASK_TIMEOUT, >> maybe setting CONFIG_RCU_CPU_STALL_TIMEOUT to smaller values (e.g. 25) can >> give us some hints... > > If an rcu stall is the true root cause of this, then I guess would see > "rcu stall" bug too. Rcu stall is detected after 120 seconds, but task > hang after 120-240 seconds. So rcu stall has much higher chances to be > detected. Do you see the corresponding "rcu stall" bug? RCU stall is detected after 125 seconds due to CONFIG_PROVE_RCU=y (e.g. https://syzkaller.appspot.com/bug?id=1fac0fd91219f3f2a03d6fa7deafc95fbed79cc2 ). I didn't find the corresponding "rcu stall" bug. But it is not required that one RCU stall takes longer than 120 seconds. down(); // Will take 120 seconds due to multiple RCU stalls rcu_read_lock(): do_something(); rcu_read_unlock(): // Took 30 seconds for unknown reason. rcu_read_lock(): do_something(); rcu_read_unlock(): // Took 30 seconds for unknown reason. rcu_read_lock(): do_something(); rcu_read_unlock(): // Took 30 seconds for unknown reason. rcu_read_lock(): do_something(); rcu_read_unlock(): // Took 30 seconds for unknown reason. up();