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Subject: Re: WARNING in __flush_work
To:     axboe@kernel.dk
References: <000000000000c1ac2805809b7cf6@google.com>
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
From:   Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Message-ID: <4d633ac8-2340-8759-f2a6-a147dafe3339@I-love.SAKURA.ne.jp>
Date:   Wed, 30 Jan 2019 22:56:43 +0900
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From fd653e8dd0d5368cd0cd9ccd89cf3001e4584f8a Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Wed, 30 Jan 2019 22:21:45 +0900
Subject: [PATCH] block: pass no-op callback to INIT_WORK().

syzbot is hitting flush_work() warning caused by commit 4d43d395fed12463
("workqueue: Try to catch flush_work() without INIT_WORK().") [1].
Although that commit did not expect INIT_WORK(NULL) case, calling
flush_work() without setting a valid callback should be avoided anyway.
Fix this problem by setting a no-op callback instead of NULL.

[1] https://syzkaller.appspot.com/bug?id=e390366bc48bc82a7c668326e0663be3b91cbd29

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-and-tested-by: syzbot <syzbot+ba2a929dcf8e704c180e@syzkaller.appspotmail.com>
Cc: Tejun Heo <tj@kernel.org>
---
 block/blk-core.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index ab17c05..4673ebe 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -462,6 +462,10 @@ static void blk_rq_timed_out_timer(struct timer_list *t)
 	kblockd_schedule_work(&q->timeout_work);
 }
 
+static void blk_timeout_work(struct work_struct *work)
+{
+}
+
 /**
  * blk_alloc_queue_node - allocate a request queue
  * @gfp_mask: memory allocation flags
@@ -504,7 +508,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
 	timer_setup(&q->backing_dev_info->laptop_mode_wb_timer,
 		    laptop_mode_timer_fn, 0);
 	timer_setup(&q->timeout, blk_rq_timed_out_timer, 0);
-	INIT_WORK(&q->timeout_work, NULL);
+	INIT_WORK(&q->timeout_work, blk_timeout_work);
 	INIT_LIST_HEAD(&q->icq_list);
 #ifdef CONFIG_BLK_CGROUP
 	INIT_LIST_HEAD(&q->blkg_list);
-- 
1.8.3.1