Messages in this thread | | | Date | Wed, 5 Jun 2013 18:37:02 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH] wait: fix false timeouts when using wait_event_timeout() |
| |
On 06/05, Imre Deak wrote: > > On Wed, 2013-06-05 at 00:35 +0300, Imre Deak wrote: > > On Tue, 2013-06-04 at 21:28 +0200, Oleg Nesterov wrote: > > > > > > Shouldn't we also change wait_event_timeout() ? Say, > > > > > > #define wait_event_timeout(wq, condition, timeout) \ > > > ({ \ > > > long __ret = timeout; \ > > > if (!(condition)) \ > > > __wait_event_timeout(wq, condition, __ret); \ > > > else if (!__ret) \ > > > __ret = 1; \ > > > __ret; \ > > > }) > > > > > > Or wait_event_timeout(timeout => 0) is not legal in a non-void context? > > > > > > To me the code like > > > > > > long wait_for_something(bool nonblock) > > > { > > > timeout = nonblock ? 0 : DEFAULT_TIMEOUT; > > > return wait_event_timeout(..., timeout); > > > } > > > > > > looks reasonable and correct. But it is not? > > > > I don't see why it would be not legal. Note though that in the above > > form wait_event_timeout(cond, 0) would still schedule() if cond is > > false, which is not what I'd expect from a non-blocking function.
Yes, if false. But what if it is true?
> Ah sorry, if you also rewrite __wait_event_timeout() then timeout=>0 > wouldn't schedule(), so things would work as expected.
Can't understand... probably you missed my point. Let me try again.
I think that wait_eveint_timeout(wq, COND, 0) should return !!(COND). But it doesn't, for example wait_event_timeout(wq, true, 0) == 0, this doesn'tlook right to me.
And, this is off-topic, but wait_eveint_timeout/__wait_eveint_timeout do not match wait_event/__wait_event. IOW, you can't use __wait_eveint_timeout() if you do not need the fast-path check.
So. How about
#define __wait_event_timeout(wq, condition, timeout) \ ({ \ DEFINE_WAIT(__wait); \ long __ret = 0, __to = timeout; \ \ for (;;) { \ prepare_to_wait(&wq, &__wait, TASK_UNINTERRUPTIBLE); \ if (condition) { \ __ret = __to ?: 1; \ break; \ } \ if (!__to) \ break; \ __to = schedule_timeout(__to); \ } \ finish_wait(&wq, &__wait); \ __ret; \ })
#define wait_event_timeout(wq, condition, timeout) \ ({ \ long __ret; \ if (condition) \ __ret = (timeout) ?: 1; \ else \ __ret = __wait_event_timeout(wq, condition, timeout); \ __ret; \ })
?
Othwerwise we should document the fact that the caller should alvays verify timeout != 0 if it checks the result of wait_event_timeout().
| |