From patchwork Tue May 1 22:14:51 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tetsuo Handa X-Patchwork-Id: 10374555 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 E24C26032A for ; Tue, 1 May 2018 22:15:17 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C6C7D28D3B for ; Tue, 1 May 2018 22:15:17 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id BB8C228D41; Tue, 1 May 2018 22:15:17 +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 42BBB28D3B for ; Tue, 1 May 2018 22:15:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751007AbeEAWPQ (ORCPT ); Tue, 1 May 2018 18:15:16 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:16347 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750859AbeEAWPP (ORCPT ); Tue, 1 May 2018 18:15:15 -0400 Received: from fsav305.sakura.ne.jp (fsav305.sakura.ne.jp [153.120.85.136]) by www262.sakura.ne.jp (8.14.5/8.14.5) with ESMTP id w41MEodd087683; Wed, 2 May 2018 07:14:50 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav305.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav305.sakura.ne.jp); Wed, 02 May 2018 07:14:50 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav305.sakura.ne.jp) Received: from AQUA (softbank126099184120.bbtec.net [126.99.184.120]) (authenticated bits=0) by www262.sakura.ne.jp (8.14.5/8.14.5) with ESMTP id w41MEnKf087679; Wed, 2 May 2018 07:14:50 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) To: axboe@kernel.dk, torvalds@linux-foundation.org Cc: jack@suse.cz, tj@kernel.org, syzbot+c0cf869505e03bdf1a24@syzkaller.appspotmail.com, christophe.jaillet@wanadoo.fr, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, zhangweiping@didichuxing.com, akpm@linux-foundation.org, dvyukov@google.com, linux-block@vger.kernel.org Subject: Re: INFO: task hung in wb_shutdown (2) From: Tetsuo Handa References: <94eb2c05b2d83650030568cc8bd9@google.com> <43302799-1c50-4cab-b974-9fe1ca584813@I-love.SAKURA.ne.jp> In-Reply-To: Message-Id: <201805020714.FDD52145.OOJtOFVFSMLQFH@I-love.SAKURA.ne.jp> X-Mailer: Winbiff [Version 2.51 PL2] X-Accept-Language: ja,en,zh Date: Wed, 2 May 2018 07:14:51 +0900 Mime-Version: 1.0 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 >From 1b90d7f71d60e743c69cdff3ba41edd1f9f86f93 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Wed, 2 May 2018 07:07:55 +0900 Subject: [PATCH v2] bdi: wake up concurrent wb_shutdown() callers. syzbot is reporting hung tasks at wait_on_bit(WB_shutting_down) in wb_shutdown() [1]. This seems to be because commit 5318ce7d46866e1d ("bdi: Shutdown writeback on all cgwbs in cgwb_bdi_destroy()") forgot to call wake_up_bit(WB_shutting_down) after clear_bit(WB_shutting_down). Introduce a helper function clear_and_wake_up_bit() and use it, in order to avoid similar errors in future. [1] https://syzkaller.appspot.com/bug?id=b297474817af98d5796bc544e1bb806fc3da0e5e Signed-off-by: Tetsuo Handa Reported-by: syzbot Fixes: 5318ce7d46866e1d ("bdi: Shutdown writeback on all cgwbs in cgwb_bdi_destroy()") Cc: Tejun Heo Cc: Jan Kara Cc: Jens Axboe Suggested-by: Linus Torvalds Reviewed-by: Jan Kara --- include/linux/wait_bit.h | 17 +++++++++++++++++ mm/backing-dev.c | 2 +- 2 files changed, 18 insertions(+), 1 deletion(-) diff --git a/include/linux/wait_bit.h b/include/linux/wait_bit.h index 9318b21..2b0072f 100644 --- a/include/linux/wait_bit.h +++ b/include/linux/wait_bit.h @@ -305,4 +305,21 @@ struct wait_bit_queue_entry { __ret; \ }) +/** + * clear_and_wake_up_bit - clear a bit and wake up anyone waiting on that bit + * + * @bit: the bit of the word being waited on + * @word: the word being waited on, a kernel virtual address + * + * You can use this helper if bitflags are manipulated atomically rather than + * non-atomically under a lock. + */ +static inline void clear_and_wake_up_bit(int bit, void *word) +{ + clear_bit_unlock(bit, word); + /* See wake_up_bit() for which memory barrier you need to use. */ + smp_mb__after_atomic(); + wake_up_bit(word, bit); +} + #endif /* _LINUX_WAIT_BIT_H */ diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 023190c..fa5e6d7 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -383,7 +383,7 @@ static void wb_shutdown(struct bdi_writeback *wb) * the barrier provided by test_and_clear_bit() above. */ smp_wmb(); - clear_bit(WB_shutting_down, &wb->state); + clear_and_wake_up_bit(WB_shutting_down, &wb->state); } static void wb_exit(struct bdi_writeback *wb)