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

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Date:	Tue, 5 Mar 2013 12:55:47 -0800
From:	Mandeep Singh Baines <msb@...omium.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Linux Kernel Mailing List <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>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] thinkpad-acpi: fix potential suspend blocking issue

On Tue, Mar 5, 2013 at 10:05 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 03/05, Mandeep Singh Baines wrote:
>>
>> On Tue, Mar 5, 2013 at 9:48 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>> > On 03/05, Mandeep Singh Baines wrote:
>> >>
>> >> @@ -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();
>> >> -
>> >
>> > I don't understand this code... but don't we have the same problem
>> > with kthread_freezable_should_stop() below? It can call __refrigerator()
>> > too under the same lock.
>> >
>>
>> I don't think the lock is held at that point. There is an unlock right
>> before entering the while loop and at the bottom of the loop.
>
> Hmm... Afaics this is another lock, hotkey_thread_data_mutex. But
> hotkey_thread_mutex is still held.
>

Ah. You're right. The two names were similar so that confused me. I'm
also looking at this code for the first time:)

This mutex seems wrong. Its held the entire time the kthread is
running. I think its used to synchronize on the exit of the kthread. A
completion would more appropriate in that case.

Regards,
Mandeep

> Oleg.
>
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