Re: 5.15-rc3+ crash in fq-codel?

On 9/27/21 5:04 PM, Ben Greear wrote:

On 9/27/21 4:49 PM, Eric Dumazet wrote:

quoted

On 9/27/21 4:30 PM, Ben Greear wrote:

quoted

Hello,

In a hacked upon kernel, I'm getting crashes in fq-codel when doing bi-directional
pktgen traffic on top of mac-vlans.  Unfortunately for me, I've made big changes to
pktgen so I cannot easily run this test on stock kernels, and there is some chance
some of my hackings have caused this issue.

But, in case others have seen similar, please let me know.  I shall go digging
in the meantime...

Looks to me like 'skb' is NULL in line 120 below.

pktgen must not be used in a mode where a single skb
is cloned and reused, if packet needs to be stored in a qdisc.

qdisc of all sorts assume skb->next/prev can be used as
anchor in their list.

If the same skb is queued multiple times, lists are corrupted.

Please double check your clone_skb pktgen setup.

I thought we had IFF_TX_SKB_SHARING for this, and that macvlan was properly clearing this bit.

My pktgen config was not using any duplicated queueing in this case.

I changed to pfifo fast and so far it is stable for ~10 minutes, where before it would crash
within a minute.  I'll let it bake overnight....

Still running stable.  I also notice we have been using fq-codel for a while and haven't noticed
this problem (next most recent kernel we might have run similar test on would be 5.13-ish).

I'll duplicate this test on our older kernels tomorrow to see if it looks like a regression or
if we just haven't actually done this exact test in a while...

Thanks,
Ben