From a9d9baa1e819b2f92f9cfa5240f766c535e636a6 Mon Sep 17 00:00:00 2001 From: Ashok Raj Date: Mon, 28 Nov 2005 13:43:46 -0800 Subject: [PATCH] clean up lock_cpu_hotplug() in cpufreq There are some callers in cpufreq hotplug notify path that the lowest function calls lock_cpu_hotplug(). The lock is already held during cpu_up() and cpu_down() calls when the notify calls are broadcast to registered clients. Ideally if possible, we could disable_preempt() at the highest caller and make sure we dont sleep in the path down in cpufreq->driver_target() calls but the calls are so intertwined and cumbersome to cleanup. Hence we consistently use lock_cpu_hotplug() and unlock_cpu_hotplug() in all places. - Removed export of cpucontrol semaphore and made it static. - removed explicit uses of up/down with lock_cpu_hotplug() so we can keep track of the the callers in same thread context and just keep refcounts without calling a down() that causes a deadlock. - Removed current_in_hotplug() uses - Removed PF_HOTPLUG_CPU in sched.h introduced for the current_in_hotplug() temporary workaround. Tested with insmod of cpufreq_stat.ko, and logical online/offline to make sure we dont have any hang situations. Signed-off-by: Ashok Raj Cc: Zwane Mwaikambo Cc: Shaohua Li Cc: "Siddha, Suresh B" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/cpu.c | 83 +++++++++++++++++++++++++++++++++++------------------------- 1 file changed, 49 insertions(+), 34 deletions(-) (limited to 'kernel') diff --git a/kernel/cpu.c b/kernel/cpu.c index d61ba88f34e..e882c6babf4 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -16,47 +16,76 @@ #include /* This protects CPUs going up and down... */ -DECLARE_MUTEX(cpucontrol); -EXPORT_SYMBOL_GPL(cpucontrol); +static DECLARE_MUTEX(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 - */ +#ifdef CONFIG_HOTPLUG_CPU +static struct task_struct *lock_cpu_hotplug_owner; +static int lock_cpu_hotplug_depth; -int current_in_cpu_hotplug(void) +static int __lock_cpu_hotplug(int interruptible) { - return (current->flags & PF_HOTPLUG_CPU); + int ret = 0; + + if (lock_cpu_hotplug_owner != current) { + if (interruptible) + ret = down_interruptible(&cpucontrol); + else + down(&cpucontrol); + } + + /* + * Set only if we succeed in locking + */ + if (!ret) { + lock_cpu_hotplug_depth++; + lock_cpu_hotplug_owner = current; + } + + return ret; } -EXPORT_SYMBOL_GPL(current_in_cpu_hotplug); +void lock_cpu_hotplug(void) +{ + __lock_cpu_hotplug(0); +} +EXPORT_SYMBOL_GPL(lock_cpu_hotplug); +void unlock_cpu_hotplug(void) +{ + if (--lock_cpu_hotplug_depth == 0) { + lock_cpu_hotplug_owner = NULL; + up(&cpucontrol); + } +} +EXPORT_SYMBOL_GPL(unlock_cpu_hotplug); + +int lock_cpu_hotplug_interruptible(void) +{ + return __lock_cpu_hotplug(1); +} +EXPORT_SYMBOL_GPL(lock_cpu_hotplug_interruptible); +#endif /* CONFIG_HOTPLUG_CPU */ /* Need to know about CPUs going up/down? */ int register_cpu_notifier(struct notifier_block *nb) { int ret; - if ((ret = down_interruptible(&cpucontrol)) != 0) + if ((ret = lock_cpu_hotplug_interruptible()) != 0) return ret; ret = notifier_chain_register(&cpu_chain, nb); - up(&cpucontrol); + unlock_cpu_hotplug(); return ret; } EXPORT_SYMBOL(register_cpu_notifier); void unregister_cpu_notifier(struct notifier_block *nb) { - down(&cpucontrol); + lock_cpu_hotplug(); notifier_chain_unregister(&cpu_chain, nb); - up(&cpucontrol); + unlock_cpu_hotplug(); } EXPORT_SYMBOL(unregister_cpu_notifier); @@ -112,13 +141,6 @@ 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) { @@ -171,7 +193,6 @@ out_thread: out_allowed: set_cpus_allowed(current, old_allowed); out: - current->flags &= ~PF_HOTPLUG_CPU; unlock_cpu_hotplug(); return err; } @@ -182,7 +203,7 @@ int __devinit cpu_up(unsigned int cpu) int ret; void *hcpu = (void *)(long)cpu; - if ((ret = down_interruptible(&cpucontrol)) != 0) + if ((ret = lock_cpu_hotplug_interruptible()) != 0) return ret; if (cpu_online(cpu) || !cpu_present(cpu)) { @@ -190,11 +211,6 @@ int __devinit cpu_up(unsigned int cpu) 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", @@ -217,7 +233,6 @@ out_notify: if (ret != 0) notifier_call_chain(&cpu_chain, CPU_UP_CANCELED, hcpu); out: - current->flags &= ~PF_HOTPLUG_CPU; - up(&cpucontrol); + unlock_cpu_hotplug(); return ret; } -- cgit v1.2.3