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SubjectRe: [PATCH 0/6] sched, wait: Collapse __wait_event macros -v4
On Mon, Sep 30, 2013 at 07:40:54PM +0200, Oleg Nesterov wrote:
> Once again, of course I do not blame this series, but
> wait_event_timeout(wq, true, 0) still returns 0.


So we have:


#define ___wait_cond_timeout(condition) \
({ \
bool __cond = (condition); \
if (__cond && !__ret) \
__ret = 1; \
__cond || !__ret; \
})

#define ___wait_event(wq, condition, state, exclusive, ret, cmd) \
({ \
__label__ __out; \
DEFINE_WAIT(__wait); \
long __ret = ret; \
\
for (;;) { \
if (exclusive) \
prepare_to_wait_exclusive(&wq, &__wait, state); \
else \
prepare_to_wait(&wq, &__wait, state); \
\
if (condition) \
break; \
\
if (___wait_signal_pending(state)) { \
__ret = -ERESTARTSYS; \
if (exclusive) { \
abort_exclusive_wait(&wq, &__wait, \
state, NULL); \
goto __out; \
} \
break; \
} \
\
cmd; \
} \
finish_wait(&wq, &__wait); \
__out: __ret; \
})

So wait_event_timeout(wq, true, 0) turns into:

({
DEFINE_WAIT(__wait);
long __ret = 0;

for (;;) {
prepare_to_wait(&wq, &__wait, TASK_UNINTERRUPTIBLE);

if (({
bool __cond = (true);
if (__cond && !__ret)
__ret = 1;
__cond || !__ret;
}))
break;

schedule();
}
finish_wait(&wq, &__wait);
__ret;
})

Which; afaict, returns 1, not 0.

> +#define ___wait_schedule_timeout(tout) \
> + if (!tout) \
> + break; \
> + tout = schedule_timeout(tout)
> +

> ___wait_event(wq, ___wait_cond_timeout(condition), \
> TASK_INTERRUPTIBLE, 0, ret, \
> spin_unlock_irq(&lock); \
> - __ret = schedule_timeout(__ret); \
> + ___wait_schedule_timeout(__ret); \
> spin_lock_irq(&lock));

You can't do that; you'll break/return without the lock held.


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