We received a bug report that /proc/PID/cmdline only shows argv[0] if the
total length of all arguments exceeds PAGE_SIZE.  The problem is that
proc_pid_cmdline checks for the presence of a NUL byte at the end of the
args list, and assumes that the application did a setproctitle if there's
any other character.

OTOH proc_pid_cmdline will read just the first PAGE_SIZE worth of arguments
at most, and if you have more arguments, it's quite likely that there won't
be a NUL byte at offset PAGE_SIZE-1.

The attached patch fixes this.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>