blob: e26278576b31148bd021a52c0980f921bfaa233a
1 | #include <linux/export.h> |
2 | #include <linux/spinlock.h> |
3 | #include <linux/atomic.h> |
4 | |
5 | /* |
6 | * This is an implementation of the notion of "decrement a |
7 | * reference count, and return locked if it decremented to zero". |
8 | * |
9 | * NOTE NOTE NOTE! This is _not_ equivalent to |
10 | * |
11 | * if (atomic_dec_and_test(&atomic)) { |
12 | * spin_lock(&lock); |
13 | * return 1; |
14 | * } |
15 | * return 0; |
16 | * |
17 | * because the spin-lock and the decrement must be |
18 | * "atomic". |
19 | */ |
20 | int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) |
21 | { |
22 | /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */ |
23 | if (atomic_add_unless(atomic, -1, 1)) |
24 | return 0; |
25 | |
26 | /* Otherwise do it the slow way */ |
27 | spin_lock(lock); |
28 | if (atomic_dec_and_test(atomic)) |
29 | return 1; |
30 | spin_unlock(lock); |
31 | return 0; |
32 | } |
33 | |
34 | EXPORT_SYMBOL(_atomic_dec_and_lock); |
35 |