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-rw-r--r--kernel/cpu.c33
1 files changed, 33 insertions, 0 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 3619e93..d61ba88 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -21,6 +21,24 @@ EXPORT_SYMBOL_GPL(cpucontrol);
static struct notifier_block *cpu_chain;
+/*
+ * Used to check by callers if they need to acquire the cpucontrol
+ * or not to protect a cpu from being removed. Its sometimes required to
+ * call these functions both for normal operations, and in response to
+ * a cpu being added/removed. If the context of the call is in the same
+ * thread context as a CPU hotplug thread, we dont need to take the lock
+ * since its already protected
+ * check drivers/cpufreq/cpufreq.c for its usage - Ashok Raj
+ */
+
+int current_in_cpu_hotplug(void)
+{
+ return (current->flags & PF_HOTPLUG_CPU);
+}
+
+EXPORT_SYMBOL_GPL(current_in_cpu_hotplug);
+
+
/* Need to know about CPUs going up/down? */
int register_cpu_notifier(struct notifier_block *nb)
{
@@ -94,6 +112,13 @@ int cpu_down(unsigned int cpu)
goto out;
}
+ /*
+ * Leave a trace in current->flags indicating we are already in
+ * process of performing CPU hotplug. Callers can check if cpucontrol
+ * is already acquired by current thread, and if so not cause
+ * a dead lock by not acquiring the lock
+ */
+ current->flags |= PF_HOTPLUG_CPU;
err = notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,
(void *)(long)cpu);
if (err == NOTIFY_BAD) {
@@ -146,6 +171,7 @@ out_thread:
out_allowed:
set_cpus_allowed(current, old_allowed);
out:
+ current->flags &= ~PF_HOTPLUG_CPU;
unlock_cpu_hotplug();
return err;
}
@@ -163,6 +189,12 @@ int __devinit cpu_up(unsigned int cpu)
ret = -EINVAL;
goto out;
}
+
+ /*
+ * Leave a trace in current->flags indicating we are already in
+ * process of performing CPU hotplug.
+ */
+ current->flags |= PF_HOTPLUG_CPU;
ret = notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
if (ret == NOTIFY_BAD) {
printk("%s: attempt to bring up CPU %u failed\n",
@@ -185,6 +217,7 @@ out_notify:
if (ret != 0)
notifier_call_chain(&cpu_chain, CPU_UP_CANCELED, hcpu);
out:
+ current->flags &= ~PF_HOTPLUG_CPU;
up(&cpucontrol);
return ret;
}
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