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Date: Mon, 9 Oct 2017 17:24:49 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>, LKML <linux-kernel@vger.kernel.org>,
        Josef Bacik <josef@toxicpanda.com>, Tejun Heo <tj@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [RFC] workqueue: Fix irq inversion deadlock in manage_workers()
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On Mon, Oct 09, 2017 at 05:40:43PM +0800, Lai Jiangshan wrote:
> I didn't thought this kind of pattern is very seldom.  I remember I saw several.

>   mutex_lock();
>   do_something();
>   spin_lock_irq();
>   record_the_state_for_ do_something().
>    // keep the spin lock held to hold the state for do_more_things().
>   mutex_unlock(); // unlock() is suggested to be called when just exiting C.S.
>   do_more_things();
>   spin_unlock_irq();
> 
> Was all code of this pattern removed?
> Could it be possible that mutex will be changed to allow this?

So I think we did something similar to the rt_mutex in:

  b4abf91047cf ("rtmutex: Make wait_lock irq safe")

And I would not be entirely against doing the same for our normal mutex,
but I've not really had time to read/think through this thread.