Hello,
Just noticed this commit...
commit 4c663cfc523a88d97a8309b04a089c27dc57fd7e
Author: Imre Deak <imre.d...@intel.com>
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?
Oleg.
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