top: forest view segmentation fault, the final solution

top: forest view segmentation fault, the final solution

With forest view mode under procps-ng-3.3.0, top would catch
a SEGV and exit.  The problem was thought to be related to
some linux version 3 anamoly.

In procps-ng-3.3.1, top was protected from abnormal exit and
would display the offending processes with the special orphan
notation '?', instead of the usual artwork.

As it turns out, the problem wasn't with linux and could
surface under a 2.6.xx kernel,  The cause was an occasional
abnormal ordering of tid/tgid/ppid which went unresolved
due to a progressive proc table scan in the recursive
function forest_add().

By default the proc table scan now restarts at the beginning.
However, a #define TREE_ONEPASS is provided should one wish
to restore the 3.3.1 behavior with its reduced overhead.