diff options
Diffstat (limited to 'arch/i386/lib/dec_and_lock.c')
-rw-r--r-- | arch/i386/lib/dec_and_lock.c | 40 |
1 files changed, 40 insertions, 0 deletions
diff --git a/arch/i386/lib/dec_and_lock.c b/arch/i386/lib/dec_and_lock.c new file mode 100644 index 00000000000..ab43394dc77 --- /dev/null +++ b/arch/i386/lib/dec_and_lock.c @@ -0,0 +1,40 @@ +/* + * x86 version of "atomic_dec_and_lock()" using + * the atomic "cmpxchg" instruction. + * + * (For CPU's lacking cmpxchg, we use the slow + * generic version, and this one never even gets + * compiled). + */ + +#include <linux/spinlock.h> +#include <asm/atomic.h> + +int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) +{ + int counter; + int newcount; + +repeat: + counter = atomic_read(atomic); + newcount = counter-1; + + if (!newcount) + goto slow_path; + + asm volatile("lock; cmpxchgl %1,%2" + :"=a" (newcount) + :"r" (newcount), "m" (atomic->counter), "0" (counter)); + + /* If the above failed, "eax" will have changed */ + if (newcount != counter) + goto repeat; + return 0; + +slow_path: + spin_lock(lock); + if (atomic_dec_and_test(atomic)) + return 1; + spin_unlock(lock); + return 0; +} |