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Subject: Re: [RT] bad BUG_ON in rtmutex.c
From: Steven Rostedt <rostedt@goodmis.org>
To: Daniel Walker <dwalker@mvista.com>
Cc: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
       LKML <linux-kernel@vger.kernel.org>
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Date: Tue, 18 Apr 2006 12:24:27 -0400
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On Tue, 2006-04-18 at 09:14 -0700, Daniel Walker wrote:

> 
> > Actually, I always thought that running PREEMPT_DESKTOP with soft and hard
> > IRQS as threads was priority ceiling.  It's just that all locks have the
> > priority of MAX_RT_PRIO (no preemption allowed).  OK, this doesn't apply
> > to mutexes, but it does apply for spin_locks. :)
> 
> Interesting way to look at it .
> 
> Reminds me of the RT read/write locks, only one read or one writer at a
> time, so it's really just a mutex ..
> 

We'll read/write doesn't work well with PI (or latencies for that
matter).  But rw_locks have one advantage over normal rt_mutex, and that
is they are self recursive.  i.e. one rw_lock can be taken over and over
again (as read) by the same process, as long as it releases it the same
amount of times.

-- Steve