linux-kernel - Re: the maxcpus= boot parameter broke somewhere along the line

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Message-ID: <x49wr5ygrfx.fsf@segfault.boston.devel.redhat.com>
Date:	Mon, 02 Apr 2012 10:05:06 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Sasha Levin <levinsasha928@...il.com>,
	Nick Bowler <nbowler@...iptictech.com>,
	linux-kernel@...r.kernel.org, Kay Sievers <kay.sievers@...y.org>
Subject: Re: the maxcpus= boot parameter broke somewhere along the line

"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com> writes:

> Looking at the mention of udev above, and considering the commit you bisected
> to, I think it would be good to see whether someone is writing 1 to
> /sys/device/system/cpu/cpu*/online and hence the cpus are getting hot-added
> towards the end of boot. Maybe that sounds stupid, but worth a try :)
>
> So can you try the debug patch below? It applies on latest linux-3.3-rc6+

Sorry it took me so long to get back to you.  You're patch did, in fact,
trigger:

udev: starting version 147
CPU 3 online initated from userspace
SMP alternatives: switching to SMP code
WARNING! power/level is deprecated; use power/control instead
Booting Node 0 Processor 3 APIC 0x3
NMI watchdog: enabled, takes one hw-pmu counter.
CPU 1 online initated from userspace
Booting Node 0 Processor 1 APIC 0x2
NMI watchdog: enabled, takes one hw-pmu counter.
CPU 2 online initated from userspace
Booting Node 0 Processor 2 APIC 0x1
NMI watchdog: enabled, takes one hw-pmu counter.
CPU 1 online initated from userspace
CPU 3 online initated from userspace
CPU 2 online initated from userspace

Checking through udev rules, I found this in
/lib/udev/rules.d/40-redhat.rules (this is a RHEL 6 install, btw):

ACTION=="add", KERNEL=="cpu[0-9]*", RUN+="/bin/bash -c 'echo 1 > /sys/devices/system/cpu/%k/online'"

So, what do you suppose is the right way to fix this?

Cheers,
Jeff

Kay, you can read up on the rest of the thread here:
https://lkml.org/lkml/2012/3/6/242
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