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/*
* 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 <linux/module.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;
}
EXPORT_SYMBOL(_atomic_dec_and_lock);
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