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/*
* 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);
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