powerpc/kprobes: Do not disable interrupts for optprobes and kprobes_on_ftrace

Per Documentation/kprobes.txt, we don't necessarily need to disable
interrupts before invoking the kprobe handlers. Masami submitted
similar changes for x86 via commit a19b2e3d783964 ("kprobes/x86: Remove
IRQ disabling from ftrace-based/optimized kprobes"). Do the same for
powerpc.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/kprobes-ftrace.c

@@ -75,11 +75,7 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip,
 {
 	struct kprobe *p;
 	struct kprobe_ctlblk *kcb;
-	unsigned long flags;
 
-	/* Disable irq for emulating a breakpoint and avoiding preempt */
-	local_irq_save(flags);
-	hard_irq_disable();
 	preempt_disable();
 
 	p = get_kprobe((kprobe_opcode_t *)nip);
@@ -105,16 +101,14 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip,
 		else {
 			/*
 			 * If pre_handler returns !0, it sets regs->nip and
-			 * resets current kprobe. In this case, we still need
-			 * to restore irq, but not preemption.
+			 * resets current kprobe. In this case, we should not
+			 * re-enable preemption.
 			 */
-			local_irq_restore(flags);
 			return;
 		}
 	}
 end:
 	preempt_enable_no_resched();
-	local_irq_restore(flags);
 }
 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
 

arch/powerpc/kernel/optprobes.c

@@ -115,14 +115,10 @@ static unsigned long can_optimize(struct kprobe *p)
 static void optimized_callback(struct optimized_kprobe *op,
 			       struct pt_regs *regs)
 {
-	unsigned long flags;
-
 	/* This is possible if op is under delayed unoptimizing */
 	if (kprobe_disabled(&op->kp))
 		return;
 
-	local_irq_save(flags);
-	hard_irq_disable();
 	preempt_disable();
 
 	if (kprobe_running()) {
@@ -135,13 +131,7 @@ static void optimized_callback(struct optimized_kprobe *op,
 		__this_cpu_write(current_kprobe, NULL);
 	}
 
-	/*
-	 * No need for an explicit __hard_irq_enable() here.
-	 * local_irq_restore() will re-enable interrupts,
-	 * if they were hard disabled.
-	 */
 	preempt_enable_no_resched();
-	local_irq_restore(flags);
 }
 NOKPROBE_SYMBOL(optimized_callback);