linux-kernel - Re: rtmutex's wait

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Date:	Tue, 24 Oct 2006 14:19:02 +0200 (CEST)
From:	Esben Nielsen <nielsen.esben@...glemail.com>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	Esben Nielsen <nielsen.esben@...glemail.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: rtmutex's wait_lock in 2.6.18-rt7



On Tue, 24 Oct 2006, Thomas Gleixner wrote:

> On Mon, 2006-10-23 at 11:55 +0200, Esben Nielsen wrote:
>> Hi,
>>   I see that in 2.6.18-rt7 the rtmutex's wait_lock is sudden interrupt
>> disabling. I don't see the need as no (hard) interrupt-handlers should be
>> touching any mutex.
>
> It does not touch mutexes, but the dynamic priority adjustment of the
> hrtimer softirq needs it.
>
> The correct solution will be moving the timer callback into the process
> context, as it will be woken up anyway, but that's more complex to do
> than it looks in the first place.
>

I have send out patches doing the correct priority adjustment without 
touching the wait_lock. Why not use that?

I found it in the archives:
  http://www.uwsg.iu.edu/hypermail/linux/kernel/0610.0/0049.html
(or more specific in 
http://www.uwsg.iu.edu/hypermail/linux/kernel/0610.0/0051.html, look for 
changes to sched.c)

It is very bad to do PI traversal in interrupt context. In the general 
case, where there are user-space locks, that operation unbounded. I 
know that in your case you can only traverse kernel locks, but I think it 
is bad to open for such posibilities if it can be avoided.


Esben

> 	tglx
>
>
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