91 lines
2 KiB
C
91 lines
2 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 semaphore'
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*
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* This mutex 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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* Note: code locked by this semaphore will only be serialized against
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* other code using the same locking facility. The code guarantees that
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* the task remains on the same CPU.
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*
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* Don't use in new code.
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*/
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static DECLARE_MUTEX(kernel_sem);
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/*
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* Re-acquire the kernel semaphore.
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*
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* This function is called with preemption off.
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*
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* We are executing in schedule() so the code must be extremely careful
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* about recursion, both due to the down() and due to the enabling of
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* preemption. schedule() will re-check the preemption flag after
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* reacquiring the semaphore.
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*/
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int __lockfunc __reacquire_kernel_lock(void)
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{
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struct task_struct *task = current;
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int saved_lock_depth = task->lock_depth;
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BUG_ON(saved_lock_depth < 0);
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task->lock_depth = -1;
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preempt_enable_no_resched();
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down(&kernel_sem);
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preempt_disable();
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task->lock_depth = saved_lock_depth;
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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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up(&kernel_sem);
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}
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/*
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* Getting the big kernel semaphore.
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*/
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void __lockfunc lock_kernel(void)
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{
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struct task_struct *task = current;
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int depth = task->lock_depth + 1;
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if (likely(!depth))
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/*
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* No recursion worries - we set up lock_depth _after_
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*/
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down(&kernel_sem);
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task->lock_depth = depth;
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}
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void __lockfunc unlock_kernel(void)
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{
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struct task_struct *task = current;
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BUG_ON(task->lock_depth < 0);
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if (likely(--task->lock_depth < 0))
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up(&kernel_sem);
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}
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EXPORT_SYMBOL(lock_kernel);
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EXPORT_SYMBOL(unlock_kernel);
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