/* * lib/kernel_lock.c * * This is the traditional BKL - big kernel lock. Largely * relegated to obsolescence, but used by various less * important (or lazy) subsystems. */#include <linux/smp_lock.h>#include <linux/module.h>#include <linux/kallsyms.h> /* * The 'big kernel semaphore' * * This mutex is taken and released recursively by lock_kernel() * and unlock_kernel().  It is transparently dropped and reacquired * over schedule().  It is used to protect legacy code that hasn't * been migrated to a proper locking design yet. * * Note: code locked by this semaphore will only be serialized against * other code using the same locking facility. The code guarantees that * the task remains on the same CPU. * * Don't use in new code. */static DECLARE_MUTEX(kernel_sem); /* * Re-acquire the kernel semaphore. * * This function is called with preemption off. * * We are executing in schedule() so the code must be extremely careful * about recursion, both due to the down() and due to the enabling of * preemption. schedule() will re-check the preemption flag after * reacquiring the semaphore. */int __lockfunc __reacquire_kernel_lock(void){	struct task_struct *task = current;	int saved_lock_depth = task->lock_depth; 	BUG_ON(saved_lock_depth < 0); 	task->lock_depth = -1;	preempt_enable_no_resched(); 	down(&kernel_sem); 	preempt_disable();	task->lock_depth = saved_lock_depth; 	return 0;} void __lockfunc __release_kernel_lock(void){	up(&kernel_sem);} /* * Getting the big kernel semaphore. */void __lockfunc lock_kernel(void){	struct task_struct *task = current;	int depth = task->lock_depth + 1; 	if (likely(!depth))		/*		 * No recursion worries - we set up lock_depth _after_		 */		down(&kernel_sem); 	task->lock_depth = depth;} void __lockfunc unlock_kernel(void){	struct task_struct *task = current; 	BUG_ON(task->lock_depth < 0); 	if (likely(--task->lock_depth < 0))		up(&kernel_sem);} EXPORT_SYMBOL(lock_kernel);EXPORT_SYMBOL(unlock_kernel);