From: Doug Chapman <dchapman@redhat.com>
Date: Fri, 11 Jan 2008 11:42:49 -0500
Subject: [cpufreq] booting with maxcpus=1 panics
Message-id: 1200069769.22739.8.camel@deimos.americas.hpqcorp.net
O-Subject: [RHEL5.2 PATCH] BZ 428331 - booting with maxcpus=1 panics when starting cpufreq service
Bugzilla: 428331

Fix for BZ 428331 - booting with maxcpus=1 panics when starting cpufreq service

Introduced by my patch for BZ 253416.  The fix is to check if the cpu is inline
cpufreq_remove_dev in the same way as it was already done in cpufreq_add_dev.

This is a direct backport of:

commit ec28297a562f2b022115b9eb82e4ea724d996240
Author: Venki Pallipadi <venkatesh.pallipadi@intel.com>
Date:   Mon Mar 26 12:03:19 2007 -0700

    [PATCH] Fix maxcpus=1 trigerring BUG() in cpufreq

    Ingo reported it on lkml in the thread
      "2.6.21-rc5: maxcpus=1 crash in cpufreq: kernel BUG at drivers/cpufreq/cpufreq.c:82!"

    This check added to remove_dev  is symmetric to one in add_dev and handles
    callbacks for offline cpus cleanly.

Tested by myself and Dave Anderson.

Acked-by: Dave Anderson <anderson@redhat.com>
Acked-by: Prarit Bhargava <prarit@redhat.com>
Acked-by: Neil Horman <nhorman@redhat.com>
Acked-by: Brian Maly <bmaly@redhat.com>

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index b2356eb..7f39618 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -972,6 +972,10 @@ static int cpufreq_remove_dev (struct sys_device * sys_dev)
 {
 	unsigned int cpu = sys_dev->id;
 	int retval;
+
+	if (cpu_is_offline(cpu))
+		return 0;
+
 	if (unlikely(lock_policy_rwsem_write(cpu)))
 		BUG();