On Friday, 16 October 2020, 09:45:42 CEST, Kurt Kanzenbach wrote: > On Thu Oct 15 2020, Christian Eggers wrote: > > On Wednesday, 14 October 2020, 19:31:03 CEST, Vladimir Oltean wrote: > >> What problem are you actually trying to solve? > > > > After (hopefully) understanding the important bits, I would like to solve > > the problem that after calling __skb_put_padto() there may be no tailroom > > for the tail tag. > > > > The conditions where this can happen are quite special. You need a > > skb->len < ETH_ZLEN and the skb must be marked as cloned. One condition > > where this happens in practice is when the skb has been selected for TX > > time stamping in dsa_skb_tx_timestamp() [cloned] and L2 is used as > > transport for PTP [size < ETH_ZLEN]. But maybe cloned sk_buffs can also > > happen for other reasons. > Hmm. I've never observed any problems using DSA with L2 PTP time > stamping with this tail tag code. What's the impact exactly? Memory > corruption? It looks like skb_put_padto() is only used by the tag_ksz driver. So it's unlikely that other drivers are affected by the same problem.
If I remember correctly, I got a skb_panic in skb_put() when adding the tail tag. But with the current kernel I didn't manage to create packets where the skb allocated by __skb_put_padto has not enough spare room for the tag tag. Either I am trying with wrong packets, or something else has been changed in between. I just sent a new patch which should solve the problem correctly here: https://patchwork.ozlabs.org/project/netdev/list/?series=208269 Best regards Christian