6 files changed, 29 insertions, 7 deletions

diff --git a/include/asm-i386/kprobes.h b/include/asm-i386/kprobes.h
index 57d157c5cf89..0730a20f6db8 100644
--- a/include/asm-i386/kprobes.h
+++ b/include/asm-i386/kprobes.h
@@ -44,6 +44,7 @@ typedef u8 kprobe_opcode_t;
 
 #define JPROBE_ENTRY(pentry)    (kprobe_opcode_t *)pentry
 #define ARCH_SUPPORTS_KRETPROBES
+#define  ARCH_INACTIVE_KPROBE_COUNT 0
 
 void arch_remove_kprobe(struct kprobe *p);
 void kretprobe_trampoline(void);
diff --git a/include/asm-ia64/kprobes.h b/include/asm-ia64/kprobes.h
index 8c0fc227f0fb..2418a787c405 100644
--- a/include/asm-ia64/kprobes.h
+++ b/include/asm-ia64/kprobes.h
@@ -82,6 +82,7 @@ struct kprobe_ctlblk {
 #define JPROBE_ENTRY(pentry)    (kprobe_opcode_t *)pentry
 
 #define ARCH_SUPPORTS_KRETPROBES
+#define  ARCH_INACTIVE_KPROBE_COUNT 1
 
 #define SLOT0_OPCODE_SHIFT      (37)
 #define SLOT1_p1_OPCODE_SHIFT   (37 - (64-46))
diff --git a/include/asm-powerpc/kprobes.h b/include/asm-powerpc/kprobes.h
index f466bc804f41..2d0af52c823d 100644
--- a/include/asm-powerpc/kprobes.h
+++ b/include/asm-powerpc/kprobes.h
@@ -50,6 +50,8 @@ typedef unsigned int kprobe_opcode_t;
                         IS_TWI(instr) || IS_TDI(instr))
 
 #define ARCH_SUPPORTS_KRETPROBES
+#define  ARCH_INACTIVE_KPROBE_COUNT 1
+
 void kretprobe_trampoline(void);
 extern void arch_remove_kprobe(struct kprobe *p);
 
diff --git a/include/asm-sparc64/kprobes.h b/include/asm-sparc64/kprobes.h
index e9bb26f770ed..15065af566c2 100644
--- a/include/asm-sparc64/kprobes.h
+++ b/include/asm-sparc64/kprobes.h
@@ -12,6 +12,7 @@ typedef u32 kprobe_opcode_t;
 
 #define JPROBE_ENTRY(pentry)    (kprobe_opcode_t *)pentry
 #define arch_remove_kprobe(p)   do {} while (0)
+#define  ARCH_INACTIVE_KPROBE_COUNT 0
 
 /* Architecture specific copy of original instruction*/
 struct arch_specific_insn {
diff --git a/include/asm-x86_64/kprobes.h b/include/asm-x86_64/kprobes.h
index 98a1e95ddb98..d36febd9bb18 100644
--- a/include/asm-x86_64/kprobes.h
+++ b/include/asm-x86_64/kprobes.h
@@ -43,6 +43,7 @@ typedef u8 kprobe_opcode_t;
 
 #define JPROBE_ENTRY(pentry)    (kprobe_opcode_t *)pentry
 #define ARCH_SUPPORTS_KRETPROBES
+#define  ARCH_INACTIVE_KPROBE_COUNT 1
 
 void kretprobe_trampoline(void);
 extern void arch_remove_kprobe(struct kprobe *p);
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 507f26e7ae7c..64aab081153b 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -47,11 +47,17 @@
 
 static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
 static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
+static atomic_t kprobe_count;
 
 DEFINE_MUTEX(kprobe_mutex);             /* Protects kprobe_table */
 DEFINE_SPINLOCK(kretprobe_lock);        /* Protects kretprobe_inst_table */
 static DEFINE_PER_CPU(struct kprobe *, kprobe_instance) = NULL;
 
+static struct notifier_block kprobe_page_fault_nb = {
+        .notifier_call = kprobe_exceptions_notify,
+        .priority = 0x7fffffff /* we need to notified first */
+};
+
 #ifdef __ARCH_WANT_KPROBES_INSN_SLOT
 /*
  * kprobe->ainsn.insn points to the copy of the instruction to be
@@ -465,6 +471,8 @@ static int __kprobes __register_kprobe(struct kprobe *p,
         old_p = get_kprobe(p->addr);
         if (old_p) {
                 ret = register_aggr_kprobe(old_p, p);
+                if (!ret)
+                        atomic_inc(&kprobe_count);
                 goto out;
         }
 
@@ -475,6 +483,10 @@ static int __kprobes __register_kprobe(struct kprobe *p,
         hlist_add_head_rcu(&p->hlist,
                        &kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);
 
+        if (atomic_add_return(1, &kprobe_count) == \
+                                (ARCH_INACTIVE_KPROBE_COUNT + 1))
+                register_page_fault_notifier(&kprobe_page_fault_nb);
+
         arch_arm_kprobe(p);
 
 out:
@@ -553,6 +565,16 @@ valid_p:
                 }
                 mutex_unlock(&kprobe_mutex);
         }
+
+        /* Call unregister_page_fault_notifier()
+         * if no probes are active
+         */
+        mutex_lock(&kprobe_mutex);
+        if (atomic_add_return(-1, &kprobe_count) == \
+                                ARCH_INACTIVE_KPROBE_COUNT)
+                unregister_page_fault_notifier(&kprobe_page_fault_nb);
+        mutex_unlock(&kprobe_mutex);
+        return;
 }
 
 static struct notifier_block kprobe_exceptions_nb = {
@@ -560,10 +582,6 @@ static struct notifier_block kprobe_exceptions_nb = {
         .priority = 0x7fffffff /* we need to be notified first */
 };
 
-static struct notifier_block kprobe_page_fault_nb = {
-        .notifier_call = kprobe_exceptions_notify,
-        .priority = 0x7fffffff /* we need to notified first */
-};
 
 int __kprobes register_jprobe(struct jprobe *jp)
 {
@@ -673,14 +691,12 @@ static int __init init_kprobes(void)
                 INIT_HLIST_HEAD(&kprobe_table[i]);
                 INIT_HLIST_HEAD(&kretprobe_inst_table[i]);
         }
+        atomic_set(&kprobe_count, 0);
 
         err = arch_init_kprobes();
         if (!err)
                 err = register_die_notifier(&kprobe_exceptions_nb);
 
-        if (!err)
-                err = register_page_fault_notifier(&kprobe_page_fault_nb);
-
         return err;
 }