kprobes/mips: Fix to check double free of insn slot

Fix to check double free of insn_slot at arch_remove_kprobe
as other arches do.
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: David Daney <ddaney@caviumnetworks.com>
Cc: Maneesh Soni <manesoni@cisco.com>
Cc: Victor Kamensky <kamensky@cisco.com>
Cc: linux-mips@linux-mips.org
Cc: Ingo Molnar <mingo@redhat.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: yrl.pp-manager.tt@hitachi.com
Cc: systemtap@sourceware.org
Patchwork: https://patchwork.linux-mips.org/patch/5293/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/kprobes.c

@@ -207,7 +207,10 @@ void __kprobes arch_disarm_kprobe(struct kprobe *p)
 
 void __kprobes arch_remove_kprobe(struct kprobe *p)
 {
-	free_insn_slot(p->ainsn.insn, 0);
+	if (p->ainsn.insn) {
+		free_insn_slot(p->ainsn.insn, 0);
+		p->ainsn.insn = NULL;
+	}
 }
 
 static void save_previous_kprobe(struct kprobe_ctlblk *kcb)