diff options
Diffstat (limited to 'kernel/cpu.c')
| -rw-r--r-- | kernel/cpu.c | 56 |
1 files changed, 23 insertions, 33 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c index 5d220234b3ca..1972b161c61e 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -58,22 +58,23 @@ static int cpu_hotplug_disabled; static struct { struct task_struct *active_writer; - struct mutex lock; /* Synchronizes accesses to refcount, */ + /* wait queue to wake up the active_writer */ + wait_queue_head_t wq; + /* verifies that no writer will get active while readers are active */ + struct mutex lock; /* * Also blocks the new readers during * an ongoing cpu hotplug operation. */ - int refcount; - /* And allows lockless put_online_cpus(). */ - atomic_t puts_pending; + atomic_t refcount; #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif } cpu_hotplug = { .active_writer = NULL, + .wq = __WAIT_QUEUE_HEAD_INITIALIZER(cpu_hotplug.wq), .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock), - .refcount = 0, #ifdef CONFIG_DEBUG_LOCK_ALLOC .dep_map = {.name = "cpu_hotplug.lock" }, #endif @@ -86,15 +87,6 @@ static struct { #define cpuhp_lock_acquire() lock_map_acquire(&cpu_hotplug.dep_map) #define cpuhp_lock_release() lock_map_release(&cpu_hotplug.dep_map) -static void apply_puts_pending(int max) -{ - int delta; - - if (atomic_read(&cpu_hotplug.puts_pending) >= max) { - delta = atomic_xchg(&cpu_hotplug.puts_pending, 0); - cpu_hotplug.refcount -= delta; - } -} void get_online_cpus(void) { @@ -103,8 +95,7 @@ void get_online_cpus(void) return; cpuhp_lock_acquire_read(); mutex_lock(&cpu_hotplug.lock); - apply_puts_pending(65536); - cpu_hotplug.refcount++; + atomic_inc(&cpu_hotplug.refcount); mutex_unlock(&cpu_hotplug.lock); } EXPORT_SYMBOL_GPL(get_online_cpus); @@ -116,8 +107,7 @@ bool try_get_online_cpus(void) if (!mutex_trylock(&cpu_hotplug.lock)) return false; cpuhp_lock_acquire_tryread(); - apply_puts_pending(65536); - cpu_hotplug.refcount++; + atomic_inc(&cpu_hotplug.refcount); mutex_unlock(&cpu_hotplug.lock); return true; } @@ -125,20 +115,18 @@ EXPORT_SYMBOL_GPL(try_get_online_cpus); void put_online_cpus(void) { + int refcount; + if (cpu_hotplug.active_writer == current) return; - if (!mutex_trylock(&cpu_hotplug.lock)) { - atomic_inc(&cpu_hotplug.puts_pending); - cpuhp_lock_release(); - return; - } - if (WARN_ON(!cpu_hotplug.refcount)) - cpu_hotplug.refcount++; /* try to fix things up */ + refcount = atomic_dec_return(&cpu_hotplug.refcount); + if (WARN_ON(refcount < 0)) /* try to fix things up */ + atomic_inc(&cpu_hotplug.refcount); + + if (refcount <= 0 && waitqueue_active(&cpu_hotplug.wq)) + wake_up(&cpu_hotplug.wq); - if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer)) - wake_up_process(cpu_hotplug.active_writer); - mutex_unlock(&cpu_hotplug.lock); cpuhp_lock_release(); } @@ -168,18 +156,20 @@ EXPORT_SYMBOL_GPL(put_online_cpus); */ void cpu_hotplug_begin(void) { - cpu_hotplug.active_writer = current; + DEFINE_WAIT(wait); + cpu_hotplug.active_writer = current; cpuhp_lock_acquire(); + for (;;) { mutex_lock(&cpu_hotplug.lock); - apply_puts_pending(1); - if (likely(!cpu_hotplug.refcount)) - break; - __set_current_state(TASK_UNINTERRUPTIBLE); + prepare_to_wait(&cpu_hotplug.wq, &wait, TASK_UNINTERRUPTIBLE); + if (likely(!atomic_read(&cpu_hotplug.refcount))) + break; mutex_unlock(&cpu_hotplug.lock); schedule(); } + finish_wait(&cpu_hotplug.wq, &wait); } void cpu_hotplug_done(void) |