v4.14-rc3/arm64 DABT exception in atomic_inc() / __skb_clone()

From: Willem de Bruijn

Sent: 25 October 2017 19:50

...

From skb->dev and netdev_priv, the tun device has flags 0x1002 ==
IFF_TAP | IFF_NO_PI. This kernel precedes the recent support for
IFF_NAPI and IFF_NAPI_FRAGS. The allocation most likely happened
in tun_build_skb from current->task_frag. It would be a previous
allocation that left alloc_frag->offset unaligned. But perhaps this code
needs to perform alignment before setting skb->head.

At least on platforms where atomic on dataref must be aligned.

Isn't that true of almost everything?
I'm not even sure x86 always (ever?) manages locked cycles on
misaligned addresses.

	David