On Tue, Sep 1, 2015 at 12:20 PM, Pravin Shelar [off-list ref] wrote:

On Tue, Sep 1, 2015 at 7:19 AM, Tom Herbert [off-list ref] wrote:

quoted

On Mon, Aug 31, 2015 at 10:15 PM, Pravin Shelar [off-list ref] wrote:

quoted

On Mon, Aug 31, 2015 at 9:12 PM, Tom Herbert [off-list ref] wrote:

quoted

On Mon, Aug 31, 2015 at 3:55 PM, Pravin B Shelar [off-list ref] wrote:

quoted

VXLAN device can receive skb with checksum partial. But the checksum
offset could be in outer header which is pulled on receive. Such skb
can cause the panic when checksum is calculated on skb. Following patch
fixes the bug by setting checksum unnecessary while pulling outer header.

Okay, I think I understand what you are doing. I suggest in the
openvswitch path, if there is a checksum CHECKSUM_PARTIAL that refers
to the outer headers which must have been verified at this point then
set to CHECKSUM_NONE-- assuming CHECKSUM_UNNECESSARY on the inner
header is not correct in this case. If the CHECKSUM_PARTIAL refers to
the inner header then you can call skb_checksum_help to resolve an
inner checksum.

That would be OVS specific fix, But I do see skb_checksum_help()
called in multiple places outside OVS that could result in similar
kernel panic. Therefore I want to solve it up in networking stack
rather than in OVS.

Please try to reproduce this out of OVS from the top of the tree then
and report down exactly where panic is occurring the code. Unlike most
of the of the other cases where skb_checksum_help() is being called
this in the RX path so skb is probably not pulled over the checksum
offset for those. Even so, if the skb is pulled beyond the checksum
offset then this should result in a negative offset in
skb_checksum_start_offset(skb) which should be okay. It looks like
this in itself should not be causing your panic.

ip_do_fragment() also calls skb_checksum_help() that can results in
similar panic. But it is not easy to reproduce it in this case due to
call site is in exception path.
The negative checksum offset can atleast cause assert failure in
skb_checksum_help(). I will send patch to fix that.

Which BUG_ON do you see is hitting?