On Thu, Jul 14, 2005 Linus Torvalds wrote:
> In other words, the _right_ way to do this is literally
>
> unsigned long timeout = jiffies + HZ/2;
> for (;;) {
> if (ready())
> return 0;
> if (time_after(timeout, jiffies))
> break;
> msleep(10);
> }
>
> which is unquestionably more complex, yes, but it's more complex because
> it is CORRECT!
Since you emphasised on correctness, your code is actually buggy
for the preemptible kernel. It could get preempted after the ready() test,
but before the time_after(), for quite a whie if a high priority process
keeps the system busy. This code is better:
unsigned long timeout = jiffies + HZ/2;
int err;
for (;;) {
err = time_after(timeout, jiffies);
if (ready())
return 0;
if (err)
break;
msleep(10);
}
This way the condition is always re-tested before reporting timeout.
Johannes
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