linux-kernel - Re: [PATCH 2.6.20-rc4 1/4] futex priority based wakeup

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Date:	Wed, 10 Jan 2007 17:29:40 +0100
From:	Pierre Peiffer <pierre.peiffer@...l.net>
To:	Daniel Walker <dwalker@...sta.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Dinakar Guniguntala <dino@...ibm.com>,
	Jean-Pierre Dion <jean-pierre.dion@...l.net>,
	Ingo Molnar <mingo@...e.hu>,
	Ulrich Drepper <drepper@...hat.com>,
	Jakub Jelinek <jakub@...hat.com>,
	Darren Hart <dvhltc@...ibm.com>,
	Sébastien Dugué <sebastien.dugue@...l.net>
Subject: Re: [PATCH 2.6.20-rc4 1/4] futex priority based wakeup

Daniel Walker a écrit :
> On Tue, 2007-01-09 at 17:16 +0100, Pierre Peiffer wrote:
>> @@ -1358,7 +1366,7 @@ static int futex_unlock_pi(u32 __user *u
>>         struct futex_hash_bucket *hb;
>>         struct futex_q *this, *next;
>>         u32 uval;
>> -       struct list_head *head;
>> +       struct plist_head *head;
>>         union futex_key key;
>>         int ret, attempt = 0;
>>
>> @@ -1409,7 +1417,7 @@ retry_locked:
>>          */
>>         head = &hb->chain;
>>
>> -       list_for_each_entry_safe(this, next, head, list) {
>> +       plist_for_each_entry_safe(this, next, head, list) {
>>                 if (!match_futex (&this->key, &key))
>>                         continue;
>>                 ret = wake_futex_pi(uaddr, uval, this);
> 
> 
> Is this really necessary? The rtmutex will priority sort the waiters
> when you enable priority inheritance. Inside the wake_futex_pi() it
> actually just pulls the new owner off another plist inside the the
> rtmutex structure.

Yes. ... necessary for non-PI-futex (ie "normal" futex)...

As the hash_bucket_list is used and common for both futex and PI-futex, yes, in 
case of PI_futex, the task is queued two times in two plist.

-- 
Pierre
-
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