From: Tetsuo Handa <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)
Date: Wed, 2 May 2018 07:14:51 +0900 [thread overview]
Message-ID: <201805020714.FDD52145.OOJtOFVFSMLQFH@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <bd3e8460-9794-6b57-e7d6-7e18ea34ac0c@kernel.dk>
>From 1b90d7f71d60e743c69cdff3ba41edd1f9f86f93 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
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 <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+c0cf869505e03bdf1a24@syzkaller.appspotmail.com>
Fixes: 5318ce7d46866e1d ("bdi: Shutdown writeback on all cgwbs in cgwb_bdi_destroy()")
Cc: Tejun Heo <tj@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@fb.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
---
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
next prev parent reply other threads:[~2018-05-01 22:15 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-01 17:10 INFO: task hung in wb_shutdown (2) syzbot
2018-04-24 12:19 ` Tetsuo Handa
2018-05-01 10:27 ` Tetsuo Handa
2018-05-01 16:06 ` Linus Torvalds
2018-05-01 21:30 ` Jens Axboe
2018-05-01 22:14 ` Tetsuo Handa [this message]
2018-05-03 15:13 ` Jan Kara
2018-05-03 15:25 ` Jens Axboe
2018-05-01 16:12 ` Jens Axboe
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