test_and_set_bit implementation

[Zoltan Menyhart]

We have got a test_and_set_bit implementation as follows:

static __inline__ int
test_and_set_bit (int nr, volatile void *addr)
{
       __u32 bit, old, new;
       volatile __u32 *m;

       m = (volatile __u32 *) addr + (nr >> 5);
       bit = 1 << (nr & 31);
       do {
               old = *m;
               new = old | bit;
       } while (cmpxchg_acq(m, old, new) != old);
       return (old & bit) != 0;
}

Let's assume the bit test & set is already set, why is then the
cmpxchg_acq() executed? Cannot we just return, e.g. like this?

       do {
               old = *m;
                if (old & bit)
                        return 1;
               new = old | bit;
       } while (cmpxchg_acq(m, old, new) != old);

Thanks,

Zoltán Menyhárt
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