| 1 | |
| 2 | * lib/kernel_lock.c
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| 3 | *
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| 4 | * This is the traditional BKL - big kernel lock. Largely
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| 5 | * relegated to obsolescence, but used by various less
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| 6 | * important (or lazy) subsystems.
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| 7 |
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| 8 | #include <linux/smp_lock.h>
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| 9 | #include <linux/module.h>
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| 10 | #include <linux/kallsyms.h>
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| 11 | #include <linux/semaphore.h>
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| 12 |
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| 13 | |
| 14 | * The 'big kernel semaphore'
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| 15 | *
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| 16 | * This mutex is taken and released recursively by lock_kernel()
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| 17 | * and unlock_kernel(). It is transparently dropped and reacquired
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| 18 | * over schedule(). It is used to protect legacy code that hasn't
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| 19 | * been migrated to a proper locking design yet.
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| 20 | *
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| 21 | * Note: code locked by this semaphore will only be serialized against
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| 22 | * other code using the same locking facility. The code guarantees that
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| 23 | * the task remains on the same CPU.
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| 24 | *
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| 25 | * Don't use in new code.
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| 26 |
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| 27 | static DECLARE_MUTEX(kernel_sem);
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| 28 |
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| 29 | |
| 30 | * Re-acquire the kernel semaphore.
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| 31 | *
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| 32 | * This function is called with preemption off.
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| 33 | *
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| 34 | * We are executing in schedule() so the code must be extremely careful
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| 35 | * about recursion, both due to the down() and due to the enabling of
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| 36 | * preemption. schedule() will re-check the preemption flag after
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| 37 | * reacquiring the semaphore.
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| 38 |
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| 39 | int __lockfunc __reacquire_kernel_lock(void)
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| 40 | {
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| 41 | struct task_struct *task = current;
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| 42 | int saved_lock_depth = task->lock_depth;
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| 43 |
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| 44 | BUG_ON(saved_lock_depth < 0);
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| 45 |
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| 46 | task->lock_depth = -1;
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| 47 | preempt_enable_no_resched();
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| 48 |
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| 49 | down(&kernel_sem);
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| 50 |
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| 51 | preempt_disable();
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| 52 | task->lock_depth = saved_lock_depth;
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| 53 |
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| 54 | return 0;
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| 55 | }
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| 56 |
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| 57 | void __lockfunc __release_kernel_lock(void)
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| 58 | {
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| 59 | up(&kernel_sem);
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| 60 | }
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| 61 |
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| 62 | |
| 63 | * Getting the big kernel semaphore.
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| 64 |
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| 65 | void __lockfunc lock_kernel(void)
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| 66 | {
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| 67 | struct task_struct *task = current;
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| 68 | int depth = task->lock_depth + 1;
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| 69 |
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| 70 | if (likely(!depth))
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| 71 | |
| 72 | * No recursion worries - we set up lock_depth _after_
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| 73 |
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| 74 | down(&kernel_sem);
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| 75 |
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| 76 | task->lock_depth = depth;
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| 77 | }
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| 78 |
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| 79 | void __lockfunc unlock_kernel(void)
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| 80 | {
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| 81 | struct task_struct *task = current;
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| 82 |
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| 83 | BUG_ON(task->lock_depth < 0);
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| 84 |
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| 85 | if (likely(--task->lock_depth < 0))
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| 86 | up(&kernel_sem);
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| 87 | }
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| 88 |
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| 89 | EXPORT_SYMBOL(lock_kernel);
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| 90 | EXPORT_SYMBOL(unlock_kernel);
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| 91 |
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