linux-kernel - Re: [PATCH] thinkpad-acpi: fix potential suspend blocking issue

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Message-Id: <20130305141817.4e27e83aa66598115e52eb9e@linux-foundation.org>
Date:	Tue, 5 Mar 2013 14:18:17 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mandeep Singh Baines <msb@...omium.org>
Cc:	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	ibm-acpi@....eng.br, ibm-acpi-devel@...ts.sourceforge.net,
	platform-driver-x86@...r.kernel.org, Aaron Lu <aaron.lu@...el.com>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	Maciej Rutecki <maciej.rutecki@...il.com>,
	Artem Savkov <artem.savkov@...il.com>
Subject: Re: [PATCH] thinkpad-acpi: fix potential suspend blocking issue

On Tue,  5 Mar 2013 09:34:43 -0800 Mandeep Singh Baines <msb@...omium.org> wrote:

> Fixes the following lockdep error:
> 
> [ BUG: ktpacpi_nvramd/446 still has locks held! ]
> 
> hotkey_kthread() calls set_freezable() after acquiring the
> hotkey_kthread_mutex(). set_freezable() calls try_to_freeze().
> This could block suspend if we were to freeze at this point
> and another task were to block on the mutex, potentially via
> writing to one of the sysfs attrs. This race is unlikely but
> can be easily fixed by moving the set_freezable() call.
>
> ...
>
> --- a/drivers/platform/x86/thinkpad_acpi.c
> +++ b/drivers/platform/x86/thinkpad_acpi.c
> @@ -2462,13 +2462,13 @@ static int hotkey_kthread(void *data)
>  	unsigned int poll_freq;
>  	bool was_frozen;
>  
> +	set_freezable();
> +
>  	mutex_lock(&hotkey_thread_mutex);
>  
>  	if (tpacpi_lifecycle == TPACPI_LIFE_EXITING)
>  		goto exit;
>  
> -	set_freezable();
> -
>  	so = 0;
>  	si = 1;
>  	t = 0;

Basically the same as
http://ozlabs.org/~akpm/mmots/broken-out/drivers-platform-x86-thinkpad_acpic-move-hotkey_thread_mutex-lock-after-set_freezable.patch.
 I think Artem's patch is a little better.  There doesn't appear to be
any locking protocol for tpacpi_lifecycle.

I'll move Artem's patch into my for-3.9-rc2 queue.
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