On 01/22/2018 09:52 PM, Sven Eckelmann wrote:
On Montag, 22. Januar 2018 20:24:50 CET Matthias Schiffer wrote:
skb_postpull_rcsum() is necessary after eth_type_trans() to adjust the skb checksum, otherwise log spam of the form "bat0: hw csum failure" will result when packets with CHECKSUM_COMPLETE are received (at least in some setups, e.g. when stacking batman-adv on top of VXLAN).
Would be nice to have a better explanation here.
The comment previously assumed that skb_pull_rcsum would be enough. But the problem here is that the skb_pull_rcsum only pulls the batman-adv headers. The actual pull of the ethernet header (with skb_pull_inline) happens inside eth_type_trans. Or did I miss anything?
This is correct, eth_type_trans() contains a simple skb_pull(), so the csum must be adjusted afterwards (grepping the kernel for eth_type_trans will find a lot of this). I can send a v2 with a better commit message later.
[...]
I don't know what the exact circumstances are that trigger the log spam, but it seems this was broken forever (I could also reproduce the issue with our compat-14 legacy branch)... so please ask David to queue this up for stable :)
Yes, this is broken since earliest commits. The most relevant commit in batman-adv is:
Fixes: fe28a94c01e1 ("batman-adv: receive packets directly using skbs")
But I would propose to use following in the kernel tree:
Fixes: c6c8fea29769 ("net: Add batman-adv meshing protocol")
The 4.15 release will be soon(tm) and Simon is currently on vacation. So we will most likely postpone the submission to David until Simon found a way out of the snow and after 4.15 is released...
But it would be nice when some people could test the patch [1] (together with vxlan?) on batman-adv or batman-adv-legacy. And please provide a "Tested-by: Full Name email@example.org" [2] reply when it works.
Thanks,> Sven
I've tested this on Kernel 4.14.14 (everything working correctly now) and 4.4.110 (here, there are still checksum errors; it seems on older kernels, the checksum handling in VXLAN is broken too? Still debugging this...)
Matthias
[1] https://patchwork.open-mesh.org/patch/17250/ [2] https://www.kernel.org/doc/html/v4.12/process/submitting-patches.html#using-...