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authorSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>2013-09-12 01:43:25 +0530
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2013-09-11 23:29:57 +0200
commit61173f256a3bebfbd09b4bd2c164dde378614091 (patch)
tree03cc6a56fba342d60e7abb94a207b1ceb650c9e8 /drivers/cpufreq/cpufreq.c
parent0d66b91ebff49841f607a3c079984c907c8a4199 (diff)
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 <srivatsa.bhat@linux.vnet.ibm.com> Tested-by: Stephen Warren <swarren@nvidia.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'drivers/cpufreq/cpufreq.c')
-rw-r--r--drivers/cpufreq/cpufreq.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 62bdb955ea56..247842b2ee2d 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1193,8 +1193,9 @@ static int __cpufreq_remove_dev_prepare(struct device *dev,
cpumask_clear_cpu(cpu, policy->cpus);
unlock_policy_rwsem_write(cpu);
- if (cpu != policy->cpu && !frozen) {
- sysfs_remove_link(&dev->kobj, "cpufreq");
+ if (cpu != policy->cpu) {
+ if (!frozen)
+ sysfs_remove_link(&dev->kobj, "cpufreq");
} else if (cpus > 1) {
new_cpu = cpufreq_nominate_new_policy_cpu(policy, cpu, frozen);