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Sender: Tejun Heo <htejun@gmail.com>
Date:   Tue, 17 Oct 2023 23:53:12 -1000
From:   Tejun Heo <tj@kernel.org>
To:     Frederic Weisbecker <frederic@kernel.org>
Cc:     Lai Jiangshan <jiangshanlai@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "Paul E . McKenney" <paulmck@kernel.org>
Subject: Re: [PATCH] workqueue: Provide one lock class key per work_on_cpu()
 callsite
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References: <20230924150702.9588-1-frederic@kernel.org>
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On Sun, Sep 24, 2023 at 05:07:02PM +0200, Frederic Weisbecker wrote:
> All callers of work_on_cpu() share the same lock class key for all the
> functions queued. As a result the workqueue related locking scenario for
> a function A may be spuriously accounted as an inversion against the
> locking scenario of function B such as in the following model:
> 
> 	long A(void *arg)
> 	{
> 		mutex_lock(&mutex);
> 		mutex_unlock(&mutex);
> 	}
> 
> 	long B(void *arg)
> 	{
> 	}
> 
> 	void launchA(void)
> 	{
> 		work_on_cpu(0, A, NULL);
> 	}
> 
> 	void launchB(void)
> 	{
> 		mutex_lock(&mutex);
> 		work_on_cpu(1, B, NULL);
> 		mutex_unlock(&mutex);
> 	}
> 
> launchA and launchB running concurrently have no chance to deadlock.
> However the above can be reported by lockdep as a possible locking
> inversion because the works containing A() and B() are treated as
> belonging to the same locking class.

Sorry about the delay. I missed this one. Applied to wq/for-6.7.

Thanks.

-- 
tejun