AW: AW: AW: PROBLEM: Kernel Oops in UDP stack

From: Marcel Hellwig
Date: Fri Aug 03 2018 - 04:24:24 EST

>Well, this driver does not use NET_IP_ALIGN reservation, meaning IP header is not 4-byte aligned.
>No idea why mis-alignments are okay in IP layer, but not in UDP
>You could try to patch it to use netdev_alloc_skb_ip_align() instead of dev_alloc_skb()

Looks very promising! CPU runs for 3 hours and no panic so far. Let's hope it survives the weekend! *fingers crossed*
The strange thing I don't understand is, why does the 3.5.7 kernel does not crash (or 4.17.12, yes I managed to run a recent kernel on our machine! \o/ )? It does not use netdev_alloc_skb_ip_align either[0][1], but one thing, that I noticed it, that there is a difference in /proc/iomem

# cat /proc/iomem
08000000-0801ffff : lpc-eth.0
31060000-31060fff : lpc-eth.0
40088000-4008801f : serial

# cat /proc/iomem
20084000-20084fff : /ahb/apb/ssp@20084000
2008c000-2008cfff : /ahb/apb/ssp@2008c000
31000000-31000fff : /ahb/dma@31000000
40088000-4008801f : serial

As you notice lpc-eth.0 (or 31060000.ethernet as it's called nowadays) is not listed, so my guess it is served by DMA?

May that the reason why it does not crash (Notice: 3.5.7 runs via device tree file)?

So just my thought: If I would disable dma (somehow) would the error still occur in today's kernel?


Mit freundlichen GrÃÃen / With kind regards

Marcel Hellwig
B. Sc. Informatik

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