linux-kernel - Re: [-rt] Fix race condition and following BUG in PI-futex

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Message-ID: <Pine.LNX.4.64.0608020007350.10605@localhost.localdomain>
Date:	Wed, 2 Aug 2006 00:28:58 +0100 (BST)
From:	Esben Nielsen <nielsen.esben@...glemail.com>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Darren Hart <dvhltc@...ibm.com>,
	Esben Nielsen <nielsen.esben@...glemail.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [-rt] Fix race condition and following BUG in PI-futex



On Tue, 1 Aug 2006, Steven Rostedt wrote:

> On Tue, 2006-08-01 at 13:22 -0700, Darren Hart wrote:
>
>>>>
>>>>   	list_del_init(&pi_state->owner->pi_state_list);
>>>>   	list_add(&pi_state->list, &new_owner->pi_state_list);
>>>>   	pi_state->owner = new_owner;
>>>> +	atomic_inc(&pi_state->refcount);
>>>
>>> There really needs to be a get_pi_state() or some variant. Having to do
>>> a manual atomic_inc is very dangerous.
>>
>> I understand the need to grab the wait_lock in order to serialize
>> rt_mutex_next_owner(), but why the addition of of the atomic_inc() and the
>> free_pi_state() ?  And if we do need them, shouldn't we place them around the
>> use of the pi_state, rather than just before the unlock calls?
>
> Hmm, is the inc really needed?  The hb->lock is held through this and
> the pi_state can't go away while that lock is held.

I was going to ask about that... If you say so they can go. I just added 
the inc/dec to be sure.

Esben

>
> -- Steve
>
>
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