How about getting rid of that TICKET_MSB mess and doing something like:
#define TICKET_MASK 0xFFFF
static inline void ticket_spin_unlock(atomic_t *tickets)
{
u32 t = *tickets;
smp_mb__before_atomic_inc();
/* Increment the low 16 bits without affecting the upper. */
if (unlikely((~t & TICKET_MASK) == 0))
atomic_add(-(atomic_t)TICKET_MASK, tickets);
else
atomic_inc(tickets);
}
That also allows up to 2^16 waiters, up from 2^15.
(Minus one on both cases, if you want to be fussy.)
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