x86: add reenter_kprobe helper

Index: b/arch/x86/kernel/kprobes.c
===================================================================
@@ -427,6 +427,38 @@ void __kprobes arch_prepare_kretprobe(st
 	/* Replace the return addr with trampoline addr */
 	*sara = (unsigned long) &kretprobe_trampoline;
 }
+/*
+ * We have reentered the kprobe_handler(), since another probe was hit while
+ * within the handler. We save the original kprobes variables and just single
+ * step on the instruction of the new probe without calling any user handlers.
+ */
+static int __kprobes reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
+				   struct kprobe_ctlblk *kcb)
+{
+	if (kcb->kprobe_status == KPROBE_HIT_SS &&
+	    *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
+		regs->flags &= ~X86_EFLAGS_TF;
+		regs->flags |= kcb->kprobe_saved_flags;
+		return 0;
+#ifdef CONFIG_X86_64
+	} else if (kcb->kprobe_status == KPROBE_HIT_SSDONE) {
+		/* TODO: Provide re-entrancy from post_kprobes_handler() and
+		 * avoid exception stack corruption while single-stepping on
+		 * the instruction of the new probe.
+		 */
+		arch_disarm_kprobe(p);
+		regs->ip = (unsigned long)p->addr;
+		reset_current_kprobe();
+		return 1;
+#endif
+	}
+	save_previous_kprobe(kcb);
+	set_current_kprobe(p, regs, kcb);
+	kprobes_inc_nmissed_count(p);
+	prepare_singlestep(p, regs);
+	kcb->kprobe_status = KPROBE_REENTER;
+	return 1;
+}
 
 /*
  * Interrupts are disabled on entry as trap3 is an interrupt gate and they

@@ -451,39 +483,9 @@ static int __kprobes kprobe_handler(stru
 	/* Check we're not actually recursing */
 	if (kprobe_running()) {
 		p = get_kprobe(addr);
-		if (p) {
-			if (kcb->kprobe_status == KPROBE_HIT_SS &&
-				*p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
-				regs->flags &= ~X86_EFLAGS_TF;
-				regs->flags |= kcb->kprobe_saved_flags;
-				goto no_kprobe;
-#ifdef CONFIG_X86_64
-			} else if (kcb->kprobe_status == KPROBE_HIT_SSDONE) {
-				/* TODO: Provide re-entrancy from
-				 * post_kprobes_handler() and avoid exception
-				 * stack corruption while single-stepping on
-				 * the instruction of the new probe.
-				 */
-				arch_disarm_kprobe(p);
-				regs->ip = (unsigned long)p->addr;
-				reset_current_kprobe();
-				ret = 1;
-				goto no_kprobe;
-#endif
-			}
-			/* We have reentered the kprobe_handler(), since
-			 * another probe was hit while within the handler.
-			 * We here save the original kprobes variables and
-			 * just single step on the instruction of the new probe
-			 * without calling any user handlers.
-			 */
-			save_previous_kprobe(kcb);
-			set_current_kprobe(p, regs, kcb);
-			kprobes_inc_nmissed_count(p);
-			prepare_singlestep(p, regs);
-			kcb->kprobe_status = KPROBE_REENTER;
-			ret = 1;
-		} else {
+		if (p)
+			ret = reenter_kprobe(p, regs, kcb);
+		else {
 			if (*addr != BREAKPOINT_INSTRUCTION) {
 			/* The breakpoint instruction was removed by
 			 * another cpu right after we hit, no further