The kernel contains an optimization that skips the linked list walk in
get_tgid_list for the common case of sequential accesses.  Unfortunately
the optimization is buggy (missing NULL pointer check for the result of
find_task_by_pid) and broken (actually - broken twice: the tgid value that
is stored in f_version is always 0 because tgid is overwritten when the
string is created and additionally the common case is not filldir < 0, it's
running out of nr_tgids).

The attached patch fixes these bugs.

Roger Luethi <rl@hellgate.ch> ran a benchmark:

	test: top -d 0 -b -n 10 > /dev/null

	==> 2.6.8 <==
	real    0m19.092s
	user    0m5.013s
	sys     0m12.622s

	==> 2.6.8 + patch-tgid-bugfixes <==
	real    0m10.062s
	user    0m5.042s
	sys     0m4.111s
Signed-Off-By: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>