Re: bug disabling guest interface

Jacek Milewicz
Wed, 06 Mar 2013 18:34:44 -0000

> I''m interested in knowing more information. Have you always been
using
> MAX_SKB_FRAGS > default_value (16 or 17) for you DomUs?

18 used to be default value on older kernels (anything older than
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/include/linux/skbuff.h?id=9d4dde5215779f4099730194ad30624fdba3d8b2
-
2011-12-23 21:51:18)

> If it is this case, you''re likely to be hitting this error path
all the
> time. It is just
> that XSA-39 chooses to shutdown vif if there is something wrong. So my
> further questions is, do you notice any performance problem in the case
> that
> netback silently drops your packets?

Basically what happened in our case is VMs were migrated to new host with
new kernel, before that dom0 used to run kernel with MAX_SKB_FRAGS==18 so it
was same for both dom0 and domU.
New host has kernel with XSA-39 fixes and smaller MAX_SKB_FRAGS (17), and
that''s when we encountered that bug, we''ve never tried kernel
with smaller
MAX_SKB_FRAGS but without XSA_39 fix.