From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: 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> Date: Wed, 2 May 2018 07:14:51 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii List-ID: >>>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 --- 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) -- 1.8.3.1 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751214AbeEAWPQ (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 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 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>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 --- 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) -- 1.8.3.1