cherry-picked from: https://patchwork.kernel.org/patch/10657429/

Enhance the stack unwinder so that it reports whether it had to stop
normally or due to an error condition; unwind_frame() will report
continue/error/normal ending and walk_stackframe() will pass that
info. __save_stack_trace() is used to check the validity of a stack;
save_stack_trace_tsk_reliable() can now trivially be implemented.
Modify arch/arm64/kernel/time.c as the only external caller so far
to recognise the new semantics.

I had to introduce a marker symbol kthread_return_to_user to tell
the normal origin of a kernel thread.
Signed-off-by: NTorsten Duwe <duwe@suse.de>
Signed-off-by: NZou Cao <zoucao@linux.alibaba.com>
Acked-by: NCaspar Zhang <caspar@linux.alibaba.com>