Linux can have pids up to 4*1024*1024.  To handle such huge numbers
pid_buf needs to be larger.
Reported-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: NRichard Weinberger <richard@nod.at>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>