linux-kernel - Re: [PATCH 2/2] workqueue: create lockdep dependency in flush

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Message-ID: <20180821160914.GQ3978217@devbig004.ftw2.facebook.com>
Date:   Tue, 21 Aug 2018 09:09:14 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        Johannes Berg <johannes.berg@...el.com>
Subject: Re: [PATCH 2/2] workqueue: create lockdep dependency in flush_work()

On Tue, Aug 21, 2018 at 02:03:17PM +0200, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@...el.com>
> 
> In flush_work(), we need to create a lockdep dependency so that
> the following scenario is appropriately tagged as a problem:
> 
>   work_function()
>   {
>     mutex_lock(&mutex);
>     ...
>   }
> 
>   other_function()
>   {
>     mutex_lock(&mutex);
>     flush_work(&work); // or cancel_work_sync(&work);
>   }
> 
> This is a problem since the work might be running and be blocked
> on trying to acquire the mutex.
> 
> Signed-off-by: Johannes Berg <johannes.berg@...el.com>

This makes sense to me.  Did you notice any extra lockdep warnings
with this?

Thanks.

-- 
tejun