CVE-2025-71115

In the Linux kernel, the following vulnerability has been resolved:

um: init cpu_tasks[] earlier

This is currently done in uml_finishsetup(), but e.g. with
KCOV enabled we'll crash because some init code can call
into e.g. memparse(), which has coverage annotations, and
then the checks in check_kcov_mode() crash because current
is NULL.

Simply initialize the cpu_tasks[] array statically, which
fixes the crash. For the later SMP work, it seems to have
not really caused any problems yet, but initialize all of
the entries anyway.