linux-kernel - Re: [HACK] convert i_alloc_sem for direct

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Message-Id: <1191271156.5574.9.camel@lappy>
Date:	Mon, 01 Oct 2007 22:39:16 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Zach Brown <zach.brown@...cle.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	mingo@...dmis.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [HACK] convert i_alloc_sem for direct_io.c craziness!

On Mon, 2007-10-01 at 12:52 -0700, Zach Brown wrote:

> Do you have any suggestions for locking constructs that RT would prefer?

Basically, anything that maps to a simple mutex. Anything more complex
gets real messy real quick.

Locks that have non-exclusive states become non-deterministic because an
unbounded number of contexts can be in this state. Hence acquisition of
the exclusive state has unbounded time. Even when limited to a bounded
number, the ramifications to the PI graph will get you a head-ache.

Also, non-owner locks, ie. semaphores (asymetric acquisition vs release
contexts) are unusable because the lack of ownership undermines PI - who
to boost?

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