On Wed, 2013-06-05 at 00:35 +0300, Imre Deak wrote: > On Tue, 2013-06-04 at 21:28 +0200, Oleg Nesterov wrote: > > Hello, > > > > Just noticed this commit... > > > > commit 4c663cfc523a88d97a8309b04a089c27dc57fd7e > > Author: Imre Deak <[email protected]> > > Date: Fri May 24 15:55:09 2013 -0700 > > > > Many callers of the wait_event_timeout() and > > wait_event_interruptible_timeout() expect that the return value will be > > positive if the specified condition becomes true before the timeout > > elapses. However, at the moment this isn't guaranteed. If the wake-up > > handler is delayed enough, the time remaining until timeout will be > > calculated as 0 - and passed back as a return value - even if the > > condition became true before the timeout has passed. > > > > OK, agreed. > > > > --- a/include/linux/wait.h > > +++ b/include/linux/wait.h > > @@ -217,6 +217,8 @@ do { > > \ > > if (!ret) > > \ > > break; > > \ > > } > > \ > > + if (!ret && (condition)) > > \ > > + ret = 1; > > \ > > finish_wait(&wq, &__wait); > > \ > > } while (0) > > > > Well, this evaluates "condition" twice, perhaps it would be more > > clean to do, say, > > > > #define __wait_event_timeout(wq, condition, ret) > > \ > > do { > > \ > > DEFINE_WAIT(__wait); > > \ > > > > \ > > for (;;) { > > \ > > prepare_to_wait(&wq, &__wait, TASK_UNINTERRUPTIBLE); > > \ > > if (condition) { > > \ > > if (!ret) > > \ > > ret = 1; > > \ > > break; > > \ > > } else if (!ret) > > \ > > break; > > \ > > ret = schedule_timeout(ret); > > \ > > } > > \ > > finish_wait(&wq, &__wait); > > \ > > } while (0) > > > > but this is minor. > > > > @@ -233,8 +235,9 @@ do { > > \ > > * wake_up() has to be called after changing any variable that could > > * change the result of the wait condition. > > * > > - * The function returns 0 if the @timeout elapsed, and the remaining > > - * jiffies if the condition evaluated to true before the timeout > > elapsed. > > + * The function returns 0 if the @timeout elapsed, or the remaining > > + * jiffies (at least 1) if the @condition evaluated to %true before > > + * the @timeout elapsed. > > > > This is still not true if timeout == 0. > > > > 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.
Ah sorry, if you also rewrite __wait_event_timeout() then timeout=>0 wouldn't schedule(), so things would work as expected. --Imre -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
