diff options
Diffstat (limited to 'kernel/cpu.c')
| -rw-r--r-- | kernel/cpu.c | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c index 3619e939182e..d61ba88f34e5 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; } |