linux-kernel - [PATCH RT 0/9][RFC] rt: Fix hotplugging and other nasties

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Date:	Thu, 01 Mar 2012 13:55:27 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	linux-kernel@...r.kernel.org,
	linux-rt-users <linux-rt-users@...r.kernel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Carsten Emde <C.Emde@...dl.org>,
	John Kacur <jkacur@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Clark Williams <clark.williams@...il.com>
Subject: [PATCH RT 0/9][RFC] rt: Fix hotplugging and other nasties

On both 3.0-rt and 3.2-rt I ran a stress test on CPU hotplug and they
both failed miserably. These bugs also show themselves on suspend.

After spending 5 long days debugging this, and finding lots of bugs
I have a patch series that makes the CPU hot plugging rather stable.

The first few patches fix other broken RT features that were discovered
while debugging hotplug.

Patch 7 is a rework of how RT handles taking down a CPU. There were
several corner cases that the original approach failed on, and this
rework seems to cover them now.

Patch 8 and 9 revert the rework that was done on workqueue for RT.
Yes, letting workqueues play games with THREAD_BOUND is bad, but
the fixes introduced several more races that were very hard to fix.
Every fix seemed to produce a new race, and it was a bad game of
cat and mouse running around a goose hunt whacking moles!

Since the rework of the CPU down code no longer had issues with
workqueue messing with THREAD_BOUND, reverting the patches that did
the rework of workqueues fixed the bugs that I was hitting.

Lets fix CPU hotplug today, and leave the redesign of workqueues
for another day.

Comments,

-- Steve

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