Races have been observed between excec-time overwriting of task->comm and
/proc accesses to the same data.  This causes environment string
information to appear in /proc.

Fix that up by taking task_lock() around updates to and accesses to
task->comm.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>