/* * 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/module.h>#include <linux/kallsyms.h>#include <linux/semaphore.h>#include <linux/smp_lock.h> #define CREATE_TRACE_POINTS#include <trace/events/bkl.h> /* * The 'big kernel lock' * * This spinlock 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. * * Don't use in new code. */static  __cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(kernel_flag);  /* * Acquire/release the underlying lock from the scheduler. * * This is called with preemption disabled, and should * return an error value if it cannot get the lock and * TIF_NEED_RESCHED gets set. * * If it successfully gets the lock, it should increment * the preemption count like any spinlock does. * * (This works on UP too - do_raw_spin_trylock will never * return false in that case) */int __lockfunc __reacquire_kernel_lock(void){	while (!do_raw_spin_trylock(&kernel_flag)) {		if (need_resched())			return -EAGAIN;		cpu_relax();	}	preempt_disable();	return 0;} void __lockfunc __release_kernel_lock(void){	do_raw_spin_unlock(&kernel_flag);	preempt_enable_no_resched();} /* * These are the BKL spinlocks - we try to be polite about preemption. * If SMP is not on (ie UP preemption), this all goes away because the * do_raw_spin_trylock() will always succeed. */#ifdef CONFIG_PREEMPTstatic inline void __lock_kernel(void){	preempt_disable();	if (unlikely(!do_raw_spin_trylock(&kernel_flag))) {		/*		 * If preemption was disabled even before this		 * was called, there's nothing we can be polite		 * about - just spin.		 */		if (preempt_count() > 1) {			do_raw_spin_lock(&kernel_flag);			return;		} 		/*		 * Otherwise, let's wait for the kernel lock		 * with preemption enabled..		 */		do {			preempt_enable();			while (raw_spin_is_locked(&kernel_flag))				cpu_relax();			preempt_disable();		} while (!do_raw_spin_trylock(&kernel_flag));	}} #else /* * Non-preemption case - just get the spinlock */static inline void __lock_kernel(void){	do_raw_spin_lock(&kernel_flag);}#endif static inline void __unlock_kernel(void){	/*	 * the BKL is not covered by lockdep, so we open-code the	 * unlocking sequence (and thus avoid the dep-chain ops):	 */	do_raw_spin_unlock(&kernel_flag);	preempt_enable();} /* * Getting the big kernel lock. * * This cannot happen asynchronously, so we only need to * worry about other CPU's. */void __lockfunc _lock_kernel(const char *func, const char *file, int line){	int depth = current->lock_depth + 1; 	trace_lock_kernel(func, file, line); 	if (likely(!depth)) {		might_sleep();		__lock_kernel();	}	current->lock_depth = depth;} void __lockfunc _unlock_kernel(const char *func, const char *file, int line){	BUG_ON(current->lock_depth < 0);	if (likely(--current->lock_depth < 0))		__unlock_kernel(); 	trace_unlock_kernel(func, file, line);} EXPORT_SYMBOL(_lock_kernel);EXPORT_SYMBOL(_unlock_kernel);