diff options
| -rw-r--r-- | drivers/cpufreq/cpufreq.c | 24 | ||||
| -rw-r--r-- | include/linux/cpu.h | 5 | ||||
| -rw-r--r-- | include/linux/sched.h | 1 | ||||
| -rw-r--r-- | kernel/cpu.c | 33 |
4 files changed, 49 insertions, 14 deletions
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 25acf478c9e8..23a63207d747 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -38,7 +38,6 @@ static struct cpufreq_driver *cpufreq_driver; static struct cpufreq_policy *cpufreq_cpu_data[NR_CPUS]; static DEFINE_SPINLOCK(cpufreq_driver_lock); - /* internal prototypes */ static int __cpufreq_governor(struct cpufreq_policy *policy, unsigned int event); static void handle_update(void *data); @@ -1115,24 +1114,21 @@ int __cpufreq_driver_target(struct cpufreq_policy *policy, int retval = -EINVAL; /* - * Converted the lock_cpu_hotplug to preempt_disable() - * and preempt_enable(). This is a bit kludgy and relies on how cpu - * hotplug works. All we need is a guarantee that cpu hotplug won't make - * progress on any cpu. Once we do preempt_disable(), this would ensure - * that hotplug threads don't get onto this cpu, thereby delaying - * the cpu remove process. - * - * We removed the lock_cpu_hotplug since we need to call this function - * via cpu hotplug callbacks, which result in locking the cpu hotplug - * thread itself. Agree this is not very clean, cpufreq community - * could improve this if required. - Ashok Raj <ashok.raj@intel.com> + * If we are already in context of hotplug thread, we dont need to + * acquire the hotplug lock. Otherwise acquire cpucontrol to prevent + * hotplug from removing this cpu that we are working on. */ - preempt_disable(); + if (!current_in_cpu_hotplug()) + lock_cpu_hotplug(); + dprintk("target for CPU %u: %u kHz, relation %u\n", policy->cpu, target_freq, relation); if (cpu_online(policy->cpu) && cpufreq_driver->target) retval = cpufreq_driver->target(policy, target_freq, relation); - preempt_enable(); + + if (!current_in_cpu_hotplug()) + unlock_cpu_hotplug(); + return retval; } EXPORT_SYMBOL_GPL(__cpufreq_driver_target); diff --git a/include/linux/cpu.h b/include/linux/cpu.h index 1f7b2c097503..43c44530ef9d 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -42,6 +42,7 @@ struct notifier_block; /* Need to know about CPUs going up/down? */ extern int register_cpu_notifier(struct notifier_block *nb); extern void unregister_cpu_notifier(struct notifier_block *nb); +extern int current_in_cpu_hotplug(void); int cpu_up(unsigned int cpu); @@ -54,6 +55,10 @@ static inline int register_cpu_notifier(struct notifier_block *nb) static inline void unregister_cpu_notifier(struct notifier_block *nb) { } +static inline int current_in_cpu_hotplug(void) +{ + return 0; +} #endif /* CONFIG_SMP */ extern struct sysdev_class cpu_sysdev_class; diff --git a/include/linux/sched.h b/include/linux/sched.h index 03b68a7b4b82..2bbf968b23d9 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -909,6 +909,7 @@ do { if (atomic_dec_and_test(&(tsk)->usage)) __put_task_struct(tsk); } while(0) #define PF_SYNCWRITE 0x00200000 /* I am doing a sync write */ #define PF_BORROWED_MM 0x00400000 /* I am a kthread doing use_mm */ #define PF_RANDOMIZE 0x00800000 /* randomize virtual address space */ +#define PF_HOTPLUG_CPU 0x01000000 /* Currently performing CPU hotplug */ /* * Only the _current_ task can read/write to tsk->flags, but other 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; } |