/proc/$pid/cmdline returns wrong value when argv[] array set to short string.

Issue

• The proc/$pid/cmdline of a process shows many x strings in the output.
• This is reproducible when an application uses setproctitle() function.

# cat /proc/54326/cmdline
oft_eb v : QMD_SQAL #10 [idle]xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

• This is reported at upstream as well.

$ for i in $(seq 1 10); do
    perl -e '$0 = "1234567890"x'"$i"'; print `cat /proc/$$/cmdline`;' | wc -c;
   done
3291
3291
3291
3291
3291
3291
71
81
91
101
$