On 07/05/2012 06:16 PM, Paolo Bonzini wrote:
> This is broken; since the eventfd is used in nonblocking mode there
> is a race between reading and writing.
>
> diff --git a/event_notifier.c b/event_notifier.c
> index 2b210f4..c339bfe 100644
> --- a/event_notifier.c
> +++ b/event_notifier.c
> @@ -51,18 +51,3 @@ int event_notifier_test_and_clear(EventNotifier *e)
> int r = read(e->fd, &value, sizeof(value));
> return r == sizeof(value);
> }
> -
> -int event_notifier_test(EventNotifier *e)
> -{
> - uint64_t value;
> - int r = read(e->fd, &value, sizeof(value));
> - if (r == sizeof(value)) {
> - /* restore previous value. */
> - int s = write(e->fd, &value, sizeof(value));
> - /* never blocks because we use EFD_SEMAPHORE.
> - * If we didn't we'd get EAGAIN on overflow
> - * and we'd have to write code to ignore it. */
> - assert(s == sizeof(value));
> - }
> - return r == sizeof(value);
> -}
I don't see the race. Mind explaining?
It does however require than a poller be extra careful when reading; and
the function is silly anyway.
--
error compiling committee.c: too many arguments to function
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