[Cake] BUG_ON vs WARN_ON

Kevin Darbyshire-Bryant kevin at darbyshire-bryant.me.uk
Fri Oct 7 09:27:32 EDT 2016

On 05/10/16 19:53, Jonathan Morton wrote:
>>> I wonder what it was that caused yesterday's issues?  I really
>>> must try again when I've more time to get proper access.
>> I’m having trouble reproducing it here.  I know one of my boxes
>> froze the very first time I loaded it, but it’s been running fine
>> ever since.  Another machine is currently refusing to insert the
>> module, claiming a wrong exec format.  It’s all a bit bizarre.
>> I do have a few more avenues of enquiry to explore, though.
> Aha - I managed to capture a kernel panic, which appears to trace to
> the lookup in the accelerator array.  It’s a read-only access, so it
> only panics if it hits unpaged memory, rather than corrupting
> anything.  Of course, if it reads outside the array, it’ll increment
> the deficit by a random value, but that usually won’t prevent traffic
> flowing.
> The lookup is indexed on the host refcnt, which I’m using as the
> count of flows attached to that host.  It seems likely that it isn’t
> being maintained correctly in all cases, so it can wrap around past
> zero very soon after being attached, without needing much traffic.
> I’ll try to fix that, and put a sanity check in as well to be
> certain.

It's now ok...so far :-)

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