linux-stable-rt/lib/kernel_lock.c

265 lines
5.6 KiB
C

/*
* lib/kernel_lock.c
*
* This is the traditional BKL - big kernel lock. Largely
* relegated to obsolescense, but used by various less
* important (or lazy) subsystems.
*/
#include <linux/smp_lock.h>
#include <linux/module.h>
#include <linux/kallsyms.h>
#if defined(CONFIG_PREEMPT) && defined(__smp_processor_id) && \
defined(CONFIG_DEBUG_PREEMPT)
/*
* Debugging check.
*/
unsigned int smp_processor_id(void)
{
unsigned long preempt_count = preempt_count();
int this_cpu = __smp_processor_id();
cpumask_t this_mask;
if (likely(preempt_count))
goto out;
if (irqs_disabled())
goto out;
/*
* Kernel threads bound to a single CPU can safely use
* smp_processor_id():
*/
this_mask = cpumask_of_cpu(this_cpu);
if (cpus_equal(current->cpus_allowed, this_mask))
goto out;
/*
* It is valid to assume CPU-locality during early bootup:
*/
if (system_state != SYSTEM_RUNNING)
goto out;
/*
* Avoid recursion:
*/
preempt_disable();
if (!printk_ratelimit())
goto out_enable;
printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] code: %s/%d\n", preempt_count(), current->comm, current->pid);
print_symbol("caller is %s\n", (long)__builtin_return_address(0));
dump_stack();
out_enable:
preempt_enable_no_resched();
out:
return this_cpu;
}
EXPORT_SYMBOL(smp_processor_id);
#endif /* PREEMPT && __smp_processor_id && DEBUG_PREEMPT */
#ifdef CONFIG_PREEMPT_BKL
/*
* The 'big kernel semaphore'
*
* This mutex is taken and released recursively by lock_kernel()
* and unlock_kernel(). It is transparently dropped and reaquired
* 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 reaquired
* 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
static inline void __lock_kernel(void)
{
preempt_disable();
if (unlikely(!_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) {
_raw_spin_lock(&kernel_flag);
return;
}
/*
* Otherwise, let's wait for the kernel lock
* with preemption enabled..
*/
do {
preempt_enable();
while (spin_is_locked(&kernel_flag))
cpu_relax();
preempt_disable();
} while (!_raw_spin_trylock(&kernel_flag));
}
}
#else
/*
* Non-preemption case - just get the spinlock
*/
static inline void __lock_kernel(void)
{
_raw_spin_lock(&kernel_flag);
}
#endif
static inline void __unlock_kernel(void)
{
_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(void)
{
int depth = current->lock_depth+1;
if (likely(!depth))
__lock_kernel();
current->lock_depth = depth;
}
void __lockfunc unlock_kernel(void)
{
BUG_ON(current->lock_depth < 0);
if (likely(--current->lock_depth < 0))
__unlock_kernel();
}
#endif
EXPORT_SYMBOL(lock_kernel);
EXPORT_SYMBOL(unlock_kernel);