134 lines
2.9 KiB
C
134 lines
2.9 KiB
C
/*
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* lib/kernel_lock.c
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*
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* This is the traditional BKL - big kernel lock. Largely
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* relegated to obsolescence, but used by various less
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* important (or lazy) subsystems.
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*/
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#include <linux/smp_lock.h>
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#include <linux/module.h>
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#include <linux/kallsyms.h>
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#include <linux/semaphore.h>
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/*
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* The 'big kernel lock'
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*
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* This spinlock is taken and released recursively by lock_kernel()
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* and unlock_kernel(). It is transparently dropped and reacquired
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* over schedule(). It is used to protect legacy code that hasn't
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* been migrated to a proper locking design yet.
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*
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* Don't use in new code.
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*/
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static __cacheline_aligned_in_smp DEFINE_SPINLOCK(kernel_flag);
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/*
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* Acquire/release the underlying lock from the scheduler.
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*
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* This is called with preemption disabled, and should
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* return an error value if it cannot get the lock and
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* TIF_NEED_RESCHED gets set.
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*
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* If it successfully gets the lock, it should increment
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* the preemption count like any spinlock does.
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*
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* (This works on UP too - _raw_spin_trylock will never
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* return false in that case)
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*/
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int __lockfunc __reacquire_kernel_lock(void)
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{
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while (!_raw_spin_trylock(&kernel_flag)) {
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if (test_thread_flag(TIF_NEED_RESCHED))
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return -EAGAIN;
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cpu_relax();
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}
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preempt_disable();
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return 0;
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}
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void __lockfunc __release_kernel_lock(void)
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{
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_raw_spin_unlock(&kernel_flag);
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preempt_enable_no_resched();
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}
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/*
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* These are the BKL spinlocks - we try to be polite about preemption.
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* If SMP is not on (ie UP preemption), this all goes away because the
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* _raw_spin_trylock() will always succeed.
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*/
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#ifdef CONFIG_PREEMPT
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static inline void __lock_kernel(void)
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{
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preempt_disable();
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if (unlikely(!_raw_spin_trylock(&kernel_flag))) {
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/*
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* If preemption was disabled even before this
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* was called, there's nothing we can be polite
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* about - just spin.
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*/
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if (preempt_count() > 1) {
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_raw_spin_lock(&kernel_flag);
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return;
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}
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/*
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* Otherwise, let's wait for the kernel lock
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* with preemption enabled..
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*/
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do {
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preempt_enable();
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while (spin_is_locked(&kernel_flag))
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cpu_relax();
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preempt_disable();
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} while (!_raw_spin_trylock(&kernel_flag));
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}
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}
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#else
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/*
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* Non-preemption case - just get the spinlock
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*/
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static inline void __lock_kernel(void)
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{
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_raw_spin_lock(&kernel_flag);
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}
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#endif
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static inline void __unlock_kernel(void)
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{
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/*
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* the BKL is not covered by lockdep, so we open-code the
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* unlocking sequence (and thus avoid the dep-chain ops):
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*/
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_raw_spin_unlock(&kernel_flag);
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preempt_enable();
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}
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/*
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* Getting the big kernel lock.
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*
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* This cannot happen asynchronously, so we only need to
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* worry about other CPU's.
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*/
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void __lockfunc lock_kernel(void)
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{
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int depth = current->lock_depth+1;
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if (likely(!depth))
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__lock_kernel();
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current->lock_depth = depth;
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}
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void __lockfunc unlock_kernel(void)
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{
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BUG_ON(current->lock_depth < 0);
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if (likely(--current->lock_depth < 0))
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__unlock_kernel();
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}
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EXPORT_SYMBOL(lock_kernel);
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EXPORT_SYMBOL(unlock_kernel);
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