linux-kernel - Re: [PATCH] workqueue: Try to catch flush_work() without INIT

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Date:   Fri, 18 Jan 2019 14:48:53 -0500
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org, daniel.m.jordan@...cle.com
Subject: Re: [PATCH] workqueue: Try to catch flush_work() without INIT_WORK().

On Sat, Jan 19, 2019 at 02:04:58AM +0900, Tetsuo Handa wrote:
> syzbot found a flush_work() caller who forgot to call INIT_WORK()
> because that work_struct was allocated by kzalloc(). But the message
> 
>   INFO: trying to register non-static key.
>   the code is fine but needs lockdep annotation.
>   turning off the locking correctness validator.
> 
> by lock_map_acquire() is failing to tell that INIT_WORK() is missing.
> 
> Since flush_work() without INIT_WORK() is a bug, and INIT_WORK() should
> set ->func field to non-zero, let's warn if ->func field is zero.

Agree that it's a good idea to catch this.  So the caller did flush_work
without queueing it beforehand?  Out of curiosity, what situation leads to
this?  Link to the report might be helpful.

> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 392be4b..a503ad9 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -2908,6 +2908,9 @@ static bool __flush_work(struct work_struct *work, bool from_cancel)
>  	if (WARN_ON(!wq_online))
>  		return false;
>  
> +	if (WARN_ON(!work->func))
> +		return false;
> +

__queue_work has a sanity check already for work, but using list_empty.  Seems
slightly better to be consistent?