Hi, All!

I compiled the latest kernel and installed it on my old laptop (Hardware name:
Hewlett-Packard HP ProBook 440 G2/2247, BIOS M74 Ver. 01.02 06/17/2014).  But
when I tried to enable function tracer via debugfs, the system went _hung_!
Compared with the last kernel compiling process, the only change I have made
is that I enabled KASAN configuration this time.

Reproducing this issue is simple as below:

        0. `uname -a` shows:
                Linux ubuntuu 5.0.0-rc2+ #9 SMP Fri Jan 18 03:04:01 CST 2019
                x86_64 x86_64 x86_64 GNU/Linux

        1. `make menuconfig` to enable KASAN configuration:
                Kernel hacking ---> Memory Debugging --->
                KASAN: runtime memory debugger

           compile, install, reboot, then `dmesg | grep kasan` shows:
                [    0.342882] kasan: KernelAddressSanitizer initialized

        2. enable function tracer
                `echo function > /sys/kernel/debug/tracing/current_tracer`
           (then my poor laptop was locked and didn't respond to me ...)

What's more, enabling function graph tracer will suffer from the same problem.
I have no idea about what wrong thing had happened inside kernel --
about ftrace,
or about KASAN?  So I report it to you and waiting for your solution!

I have provided my *.config* file as attachment for those who're interested in
this issue.  But sorry for that I can't provide any useful call trace
because the
system went down so quickly.

P.S. I'm a newcomer for KASAN. If any mis-configuration or
mis-understand, please
fix me up and let me know :).


Thanks!
Zenghui