Re: [RFC PATCH 27/33] Add the Xen virtual console driver.

From: Keir Fraser
Date: Tue Jul 18 2006 - 06:30:08 EST

On 18 Jul 2006, at 11:24, Arjan van de Ven wrote:

hmm somehow I find this code scary; we had similar code recently
elsewhere where this turned out to be a real issue; you now sleep for
"1" time, so you sleep for a fixed time if you aren't getting wakeups,
but if you are getting wakeups your code is upside down, I would expect
it to look like

+ set_current_state(TASK_INTERRUPTIBLE);
+ while (DRV(tty->driver)->chars_in_buffer(tty))
+ schedule_timeout(1);
+ if (signal_pending(current))
+ break;
+ if (timeout && time_after(jiffies, orig_jiffies + timeout))
+ break;
+ set_current_state(TASK_INTERRUPTIBLE);
+ }

instead, so that you don't have the wakeup race..

There's no wakeup signal, so no possibility of a wakeup race. That's why we schedule_timeout() instead of wait_event() or similar. This code is only used to flush the console when the kernel crashes, so we can get the full oops, so waiting a little bit too long is acceptable.

Your suggested change is perhaps more idiomatic though, and less jarring for reviewers. :-)

Thanks for your comments by the way. Reviewing lots of patches isn't much fun.

-- Keir

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