cpufreq: Restructure if/else block to avoid unintended behavior
cpufreq: Restructure if/else block to avoid unintended behavior

In __cpufreq_remove_dev_prepare(), the code which decides whether to remove
the sysfs link or nominate a new policy cpu, is governed by an if/else block
with a rather complex set of conditionals. Worse, they harbor a subtlety
which leads to certain unintended behavior.

The code looks like this:

        if (cpu != policy->cpu && !frozen) {
                sysfs_remove_link(&dev->kobj, "cpufreq");
        } else if (cpus > 1) {
		new_cpu = cpufreq_nominate_new_policy_cpu(...);
		...
		update_policy_cpu(..., new_cpu);
	}

The original intention was:
If the CPU going offline is not policy->cpu, just remove the link.
On the other hand, if the CPU going offline is the policy->cpu itself,
handover the policy->cpu job to some other surviving CPU in that policy.

But because the 'if' condition also includes the 'frozen' check, now there
are *two* possibilities by which we can enter the 'else' block:

1. cpu == policy->cpu (intended)
2. cpu != policy->cpu && frozen (unintended)

Due to the second (unintended) scenario, we end up spuriously nominating
a CPU as the policy->cpu, even when the existing policy->cpu is alive and
well. This can cause problems further down the line, especially when we end
up nominating the same policy->cpu as the new one (ie., old == new),
because it totally confuses update_policy_cpu().

To avoid this mess, restructure the if/else block to only do what was
originally intended, and thus prevent any unwelcome surprises.

Signed-off-by: Srivatsa S. Bhat <5b23f8226e886b22344fc642373ea657dd596b63@linux.vnet.ibm.com>
Tested-by: Stephen Warren <5ef2a23ba3aff51d1cfc8c113c1ec34b608b3b13@nvidia.com>
Signed-off-by: Rafael J. Wysocki <27ffc44a8ec6a212fba98cfc3246c6ce8ab131e0@intel.com>

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