[Cake] Long-RTT broken again

Kevin Darbyshire-Bryant kevin at darbyshire-bryant.me.uk
Tue Nov 3 05:29:56 EST 2015

On 03/11/15 08:34, Sebastian Moeller wrote:

> Hi Jonathan,
> On Nov 3, 2015, at 09:25 , Jonathan Morton <chromatix99 at gmail.com> wrote:
>>> On 3 Nov, 2015, at 10:20, Sebastian Moeller <moeller0 at gmx.de> wrote:
>>> Also what about the BUG_ON I managed to trigger during my testing?
>> That turned out to be a flawed condition, which I’ve already fixed.
If my git-blame-fu is working right this morning, then Dave is the one
who with the aid of commit c4f75d38 turned "BUG_ON(CAKE_MAX_BINS <
q->bin_cnt);" into "BUG_ON(q->bin_cnt >= CAKE_MAX_BINS);" and introduced
a classic 'off-by-one/fencepost' error on 2015-10-05.  A reconfigure
using 'diffserv8' should have blown up quite nicely after that date and
suggests little testing has been done with diffserv8 since that time.

Well done Seb for clearly treading rarely visited areas of the code!

BUG_ON I put in the category of "Never test for a condition you don't
know how to handle" ;-)  Now that the off-by-one has been stomped on I'm
going to stick my neck out and say that bin_cnt > 8 implies something
has stomped on our config structure and we really shouldn't be trusting
anything in it.  Goodness knows what our skb queues are like...and err,
help!  Also note that the correctly written BUG_ON didn't explode for
many months.

I'm happy with it being there.

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