linux-kernel - Re: [PATCH 1/2] genirq: Fix the possible synchronize

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Message-ID: <alpine.DEB.2.02.1402100951290.21991@ionos.tec.linutronix.de>
Date:	Mon, 10 Feb 2014 09:58:25 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Chuansheng Liu <chuansheng.liu@...el.com>
cc:	linux-kernel@...r.kernel.org,
	xiaoming wang <xiaoming.wang@...el.com>
Subject: Re: [PATCH 1/2] genirq: Fix the possible synchronize_irq()
 wait-forever

On Mon, 10 Feb 2014, Chuansheng Liu wrote:
> There is below race between irq handler and irq thread:
> irq handler                             irq thread
> 
> irq_wake_thread()                       irq_thread()
>   set bit RUNTHREAD
>   ...                                    clear bit RUNTHREAD
>                                          thread_fn()
>                                          [A]test_and_decrease
>                                                thread_active
>   [B]increase thread_active
> 
> If action A is before action B, after that the thread_active
> will be always > 0, and for synchronize_irq() calling, which
> will be waiting there forever.

No. thread_active is 0, simply because after the atomic_dec_and_test()
it is -1 and the atomic_inc on the other side will bring it back to 0.

Thanks,

	tglx
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