Definitively it should be a kernel issue since booting with my old Jaunty kernel solves the problem:
$ uname -a
Linux netbook 2.6.28-15-generic #49-Ubuntu SMP Tue Aug 18 18:40:08 UTC 2009 i686 GNU/Linux
with this kernel I do not have kernel mode switching as expected.
At the same time, a minor issue with brightness control has solved and USB devices works again (they stopped working with karmic as well), although these should be reported as a different bug.
Definitively it should be a kernel issue since booting with my old Jaunty kernel solves the problem:
$ uname -a
Linux netbook 2.6.28-15-generic #49-Ubuntu SMP Tue Aug 18 18:40:08 UTC 2009 i686 GNU/Linux
with this kernel I do not have kernel mode switching as expected.
At the same time, a minor issue with brightness control has solved and USB devices works again (they stopped working with karmic as well), although these should be reported as a different bug.