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

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Message-ID: <20190125153107.GI50184@devbig004.ftw2.facebook.com>
Date:   Fri, 25 Jan 2019 07:31:07 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Daniel Jordan <daniel.m.jordan@...cle.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] workqueue: Try to catch flush_work() without INIT_WORK().

On Wed, Jan 23, 2019 at 09:44:12AM +0900, Tetsuo Handa wrote:
> Daniel Jordan wrote:
> > On Sat, Jan 19, 2019 at 11:41:22AM +0900, Tetsuo Handa wrote:
> > > On 2019/01/19 4:48, Daniel Jordan wrote:
> > > > On Sat, Jan 19, 2019 at 02:04:58AM +0900, Tetsuo Handa wrote:
> > > > __queue_work has a sanity check already for work, but using list_empty.  Seems
> > > > slightly better to be consistent?
> > > > 
> > > 
> > > list_empty() won't work, for "struct work_struct" is embedded into a struct
> > > which is allocated by kzalloc().
> > 
> > Please check list_empty's definition again, it compares the address of the node
> > to its next pointer, so it should work for a zeroed node.  I'll reiterate that
> > it seems slightly better to be consistent in "is work_struct initialized?"
> > checks, but it's not a big deal and I'm fine either way.
> 
> You are talking about
> 
> 	if (WARN_ON(!list_empty(&work->entry))) {
> 		spin_unlock(&pwq->pool->lock);
> 		return;
> 	}
> 
> part in __queue_work(), aren't you? But since flush_work() is used for waiting for
> a work to complete, that work can be either queued state (list_empty() == false) or
> not queued state (list_empty() == true). Thus, I don't think that flush_work() can
> use list_empty() for checking whether that work was initialized.
> 
> 
> 
> [PATCH v2] workqueue: Try to catch flush_work() without INIT_WORK().
> 
> syzbot found a flush_work() caller who forgot to call INIT_WORK()
> because that work_struct was allocated by kzalloc() [1]. 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.
> 
> [1] https://syzkaller.appspot.com/bug?id=a5954455fcfa51c29ca2ab55b203076337e1c770
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>

Applied to wq/for-5.0.

Thanks.

-- 
tejun