Revert "kprobes: Warn if optprobe handler tries to change execution path"

This reverts commit:

  e863d539614641 ("kprobes: Warn if optprobe handler tries to change execution path")

On PowerPC, we place a probe at kretprobe_trampoline to catch function
returns and with CONFIG_OPTPROBES=y, this probe gets optimized. This
works for us due to the way we handle the optprobe as described in
commit:

  762df10bad6954 ("powerpc/kprobes: Optimize kprobe in kretprobe_trampoline()")

With the above commit, we end up with a warning. As such, revert this change.

Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20171017081834.3629-1-naveen.n.rao@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/kprobes.c

@@ -387,10 +387,7 @@ void opt_pre_handler(struct kprobe *p, struct pt_regs *regs)
 	list_for_each_entry_rcu(kp, &p->list, list) {
 		if (kp->pre_handler && likely(!kprobe_disabled(kp))) {
 			set_kprobe_instance(kp);
-			if (kp->pre_handler(kp, regs)) {
-				if (WARN_ON_ONCE(1))
-					pr_err("Optprobe ignores instruction pointer changing.(%pF)\n", p->addr);
-			}
+			kp->pre_handler(kp, regs);
 		}
 		reset_kprobe_instance();
 	}