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1da177e4 LT |
1 | #include <linux/module.h> |
2 | #include <linux/spinlock.h> | |
3 | #include <asm/atomic.h> | |
4 | ||
5 | /* | |
6 | * This is an architecture-neutral, but slow, | |
7 | * implementation of the notion of "decrement | |
8 | * a reference count, and return locked if it | |
9 | * decremented to zero". | |
10 | * | |
11 | * NOTE NOTE NOTE! This is _not_ equivalent to | |
12 | * | |
13 | * if (atomic_dec_and_test(&atomic)) { | |
14 | * spin_lock(&lock); | |
15 | * return 1; | |
16 | * } | |
17 | * return 0; | |
18 | * | |
19 | * because the spin-lock and the decrement must be | |
20 | * "atomic". | |
21 | * | |
22 | * This slow version gets the spinlock unconditionally, | |
23 | * and releases it if it isn't needed. Architectures | |
24 | * are encouraged to come up with better approaches, | |
25 | * this is trivially done efficiently using a load-locked | |
26 | * store-conditional approach, for example. | |
27 | */ | |
28 | ||
29 | #ifndef ATOMIC_DEC_AND_LOCK | |
30 | int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) | |
31 | { | |
32 | spin_lock(lock); | |
33 | if (atomic_dec_and_test(atomic)) | |
34 | return 1; | |
35 | spin_unlock(lock); | |
36 | return 0; | |
37 | } | |
38 | ||
39 | EXPORT_SYMBOL(_atomic_dec_and_lock); | |
40 | #endif |