/* * 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);