On Sat, 31 Oct 2015, George Spelvin wrote: > > Don't we need to keep that NULL init? I might be missing something. > > I wondered the same thing, but on reading it, the cleanup is that he's > gotten rid of the need for the entire thing. Previously, there was a > mechanism for detecting "wakeup not quite finished" that used a NULL > value, but it's no longer needed. > > The resultant busy-waiting on the part of the woken-up task was the > entire problem this patch aims to fix. So it gets rid of a whole lot > of code and barriers. And, as you noticed, the comments explaining them. > > As the old code explained, the issue is that a task may exit as > soon as r_msg is set, so the wakeup procedure has to be: > - Ensure r_msg is set to NULL (special-case flag) > - Do the wake up > - Set r_msg to the final value > > The woken-up task has to spin as long as r_msg is NULL. Ick. > > However, a wake_q keeps a reference to a task, so exiting is > not a danger. As long as wake_q_add precedes setting r_msg, > all is well.
Right. I figured that after staring some more into it. Though it would be nice if exactly that explanation is in the code. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/