IOV iterator bug in net tree (was Re: Deadlock when running DevStack on latest pull of net tree)

From: Alexander Duyck
Date: Sat May 28 2016 - 00:39:11 EST

On Fri, May 27, 2016 at 11:21 AM, Alexander Duyck
<alexander.duyck@xxxxxxxxx> wrote:
> I started out this morning by trying to run DevStack on the latest
> "net' kernel and it looks like I am hanging on some sort of locking
> problem with RabbitMQ. Specifically I am seeing one CPU jump to 100%
> with perf showing that I am spinning on a lock.
> I'm working to bisect it now, but just thought I would put it out
> there if anybody had already root caused this issue. Below is a few
> traces to the spin lock call on the spinning CPU:

I misread the perf trace. I wasn't spinning on a lock I was spinning
on the IOV iterator. It just happened to push the lock to the top of
the perf trace. I bisected it down to the recent change in
iterate_and_advance which was already fixed in Linus's tree in commit
19f18459330f "do 'fold checks into iterate_and_advance()" right'.

- Alex