Hugh Dickins a écrit :
On Thu, 6 Oct 2005, Linus Torvalds wrote:
If you want to notify another CPU that you want the spinlock, then you
need to set the "flag" variable _outside_ of the spinlock.
Spinlocks are not fair, not by a long shot. They never have been, and they
never will. Fairness would be extremely expensive indeed.
That reminds me: ought cond_resched_lock to be doing something more?
int cond_resched_lock(spinlock_t *lock)
{
int ret = 0;
if (need_lockbreak(lock)) {
spin_unlock(lock);
cpu_relax();
ret = 1;
spin_lock(lock);
}
-
Isnt it funny that some bugs can spot other bugs ? :)
break_lock should be declared atomic_t and used like that :
void __lockfunc _##op##_lock(locktype##_t *lock)
{
preempt_disable();
for (;;) {
if (likely(_raw_##op##_trylock(lock)))
break;
preempt_enable();
atomic_inc(&(lock)->break_lock);
while (!op##_can_lock(lock))
cpu_relax();
preempt_disable();
atomic_dec(&(lock)->break_lock);
}
}
Eric
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