Terve, On 09/01/12 20:14, Sakari Ailus wrote: > Moi, > > On Thu, Aug 30, 2012 at 08:54:24PM +0300, Timo Kokkonen wrote: >> @@ -273,9 +281,18 @@ static ssize_t lirc_rx51_write(struct file *file, const >> char *buf, >> >> /* >> * Don't return back to the userspace until the transfer has >> - * finished >> + * finished. However, we wish to not spend any more than 500ms >> + * in kernel. No IR code TX should ever take that long. >> + */ >> + i = wait_event_timeout(lirc_rx51->wqueue, lirc_rx51->wbuf_index < 0, >> + HZ / 2); > > Why such an arbitrary timeout? In reality it might not bite the user space > in practice ever, but is it (and if so, why) really required in the first > place?
Well, I can think of two cases: 1) Something goes wrong. Such before I converted the patch to use the up to date PM QoS implementation, the transmitting could take very long time because the interrupts were not waking up the MPU. Now that this is sorted out only unknown bugs can cause transmitting to hang indefinitely. 2) User is (intentionally?) doing something wrong. For example by feeding in an IR code that has got very long pulses, he could end up having the lircd process hung in kernel unkillable for long time. That could be avoided quite easily by counting the pulse lengths and rejecting any IR codes that are obviously too long. But since I'd like to also protect against 1) case, I think this solution works just fine. In the end, this is just safety measure that this driver behaves well. -Timo -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
