linux-kernel - Re: cpu hotplug support broken in 2.6.23-rc3

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Date:	Tue, 28 Aug 2007 12:30:40 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	Jeff Chua <jeff.chua.linux@...il.com>, vatsa@...ibm.com,
	zwane@....linux.org.uk, kernel list <linux-kernel@...r.kernel.org>,
	satyam@...radead.org, akinobu.mita@...il.com, ashok.raj@...el.com,
	ego@...ibm.com, rusty@...tcorp.com.au
Subject: Re: cpu hotplug support broken in 2.6.23-rc3

On Monday, 27 August 2007 23:58, Pavel Machek wrote:
> On Mon 2007-08-27 23:59:31, Rafael J. Wysocki wrote:
> > On Monday, 27 August 2007 23:32, Pavel Machek wrote:
> > > On Mon 2007-08-27 22:36:57, Jeff Chua wrote:
> > > > On 8/27/07, Pavel Machek <pavel@....cz> wrote:
> > > > > On Mon 2007-08-27 12:43:50, Pavel Machek wrote:
> > > > > > Hi!
> > > > > >
> > > > > > Trying to do few onlines/offlines reliably hangs my machine (thinkpad
> > > > > > x60, i386 architecture).
> > > > 
> > > > I just 3 cycles of on-line/off-line on 2.6.23-rc3 on ThinkPad x60s,
> > > > and my system still survives.
> > > 
> > > Can you try 20-or-so tests? Mine hangs randomly, so it survived 4 or
> > > so cycles at one point.
> > > 
> > > ...or maybe difference is in the .config, or maybe I broken something
> > > in my kernel sources....
> > 
> > Well, something seems to be wrong with the CPU hotplug, but it's insanely
> > difficult to reproduce on my boxes.
> > 
> > I bet on one of the notifiers blocking while waiting on a frozen task.
> 
> It happens reliably for me, with this script... and randomly, when I
> just echo 0/1 > online from commandline... so it should not be
> anything with the frozen tasks.

That suggests the CPU hotplug just deadlocks internally.

Can you put some printk's into _cpu_down() and see where exactly it hangs?

> echo test > /sys/power/disk
> echo disk > /sys/power/state
> 
> reliably hangs on resume in the attached script. It works ok with
> nosmp.

Which step hangs it?  Or is it at random?

Rafael


> #!/bin/bash
> killall klogd
> 
> echo -n "testing refrigerator (testproc)..."
> echo testproc > /sys/power/disk
> echo disk > /sys/power/state
> echo "okay"
> 
> sleep 2
> echo -n "testing drivers (test)..."
> echo test > /sys/power/disk
> echo disk > /sys/power/state
> echo "okay"
> 
> sleep 2
> echo -n "testing swsusp (reboot)..."
> echo reboot > /sys/power/disk
> echo disk > /sys/power/state
> echo "okay"
> 
> sleep 2
> echo -n "testing s2ram..."
> s2ram
> echo "okay"
> 
> sleep 2
> echo -n "testing swsusp (shutdown)..."
> echo shutdown > /sys/power/disk
> echo disk > /sys/power/state
> echo "okay"
> 
> sleep 2
> echo -n "testing swsusp (platform)..."
> echo platform > /sys/power/disk
> echo disk > /sys/power/state
> echo "okay"
> 
> sleep 2
> echo -n "testing s2ram..."
> s2ram
> echo "okay"
>  
> 

-- 
"Premature optimization is the root of all evil." - Donald Knuth
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