#ifndef __LINUX_SMPLOCK_H #define __LINUX_SMPLOCK_H #ifdef CONFIG_LOCK_KERNEL
//判断内核是否支持内核锁
//而s3c2410中arch/arm/configs/s3c2410的Code maturity level options下没有定义，所以lock_kernel()什么也不做
#include <linux/sched.h> #include <linux/spinlock.h> #define kernel_locked() (current->lock_depth >= 0) extern int __lockfunc __reacquire_kernel_lock(void); extern void __lockfunc __release_kernel_lock(void); /* * Release/re-acquire global kernel lock for the scheduler */ #define release_kernel_lock(tsk) do { \ if (unlikely((tsk)->lock_depth >= 0)) \ __release_kernel_lock(); \ } while (0) /* * Non-SMP kernels will never block on the kernel lock, * so we are better off returning a constant zero from * reacquire_kernel_lock() so that the compiler can see * it at compile-time. */ #if defined(CONFIG_SMP) && !defined(CONFIG_PREEMPT_BKL) # define return_value_on_smp return #else # define return_value_on_smp #endif static inline int reacquire_kernel_lock(struct task_struct *task) { if (unlikely(task->lock_depth >= 0)) return_value_on_smp __reacquire_kernel_lock(); return 0; } extern void __lockfunc lock_kernel(void) __acquires(kernel_lock); extern void __lockfunc unlock_kernel(void) __releases(kernel_lock); #else #define lock_kernel() do { } while(0) #define unlock_kernel() do { } while(0) #define release_kernel_lock(task) do { } while(0) #define reacquire_kernel_lock(task) 0 #define kernel_locked() 1 #endif /* CONFIG_LOCK_KERNEL */ #endif /* __LINUX_SMPLOCK_H */
//如果定义了CONFIG_LOCK_KERNEL，则转到下面代码
//判断是使用big kernel semaphore还是big kernel lock
//而s3c2410中arch/arm/configs/s3c2410中没有定义
#ifdef CONFIG_PREEMPT_BKL //判断是使用big kernel semaphore还是big kernel lock //而s3c2410中arch/arm/configs/s3c2410中没有定义 /* * 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); } #else /* * 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_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 - _raw_spin_trylock will never * return false in that case) */ int __lockfunc __reacquire_kernel_lock(void) { while (!_raw_spin_trylock(&kernel_flag)) { if (test_thread_flag(TIF_NEED_RESCHED)) return -EAGAIN; cpu_relax(); } preempt_disable(); return 0; } void __lockfunc __release_kernel_lock(void) { _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 * _raw_spin_trylock() will always succeed. */ #ifdef CONFIG_PREEMPT