[PATCH] Kprobes: preempt_disable/enable() simplification

Reorganize the preempt_disable/enable calls to eliminate the extra preempt
depth.  Changes based on Paul McKenney's review suggestions for the kprobes
RCU changeset.

Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 15 insertions, 14 deletions

diff --git a/arch/x86_64/kernel/kprobes.c b/arch/x86_64/kernel/kprobes.c
index 9bef2c8dc12c..dddeb678b440 100644
--- a/arch/x86_64/kernel/kprobes.c
+++ b/arch/x86_64/kernel/kprobes.c
@@ -286,16 +286,19 @@ void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
         }
 }
 
-/*
- * Interrupts are disabled on entry as trap3 is an interrupt gate and they
- * remain disabled thorough out this function.
- */
 int __kprobes kprobe_handler(struct pt_regs *regs)
 {
 	struct kprobe *p;
 	int ret = 0;
 	kprobe_opcode_t *addr = (kprobe_opcode_t *)(regs->rip - sizeof(kprobe_opcode_t));
-	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	struct kprobe_ctlblk *kcb;
+
+	/*
+	 * We don't want to be preempted for the entire
+	 * duration of kprobe processing
+	 */
+	preempt_disable();
+	kcb = get_kprobe_ctlblk();
 
 	/* Check we're not actually recursing */
 	if (kprobe_running()) {
@@ -359,11 +362,6 @@ int __kprobes kprobe_handler(struct pt_regs *regs)
 		goto no_kprobe;
 	}
 
-	/*
-	 * This preempt_disable() matches the preempt_enable_no_resched()
-	 * in post_kprobe_handler()
-	 */
-	preempt_disable();
 	set_current_kprobe(p, regs, kcb);
 	kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 
@@ -377,6 +375,7 @@ ss_probe:
 	return 1;
 
 no_kprobe:
+	preempt_enable_no_resched();
 	return ret;
 }
 
@@ -448,8 +447,8 @@ int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
 
         /*
          * By returning a non-zero value, we are telling
-         * kprobe_handler() that we have handled unlocking
-	 * and re-enabling preemption
+         * kprobe_handler() that we don't want the post_handler
+	 * to run (and have re-enabled preemption)
          */
         return 1;
 }
@@ -594,7 +593,6 @@ int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 	struct die_args *args = (struct die_args *)data;
 	int ret = NOTIFY_DONE;
 
-	rcu_read_lock();
 	switch (val) {
 	case DIE_INT3:
 		if (kprobe_handler(args->regs))
@@ -606,14 +604,16 @@ int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 		break;
 	case DIE_GPF:
 	case DIE_PAGE_FAULT:
+		/* kprobe_running() needs smp_processor_id() */
+		preempt_disable();
 		if (kprobe_running() &&
 		    kprobe_fault_handler(args->regs, args->trapnr))
 			ret = NOTIFY_STOP;
+		preempt_enable();
 		break;
 	default:
 		break;
 	}
-	rcu_read_unlock();
 	return ret;
 }
 
@@ -675,6 +675,7 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 		*regs = kcb->jprobe_saved_regs;
 		memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
 		       MIN_STACK_SIZE(stack_addr));
+		preempt_enable_no_resched();
 		return 1;
 	}
 	return 0;