[PATCH] Notify page fault call chain

With this patch Kprobes now registers for page fault notifications only when
their is an active probe registered.  Once all the active probes are
unregistered their is no need to be notified of page faults and kprobes
unregisters itself from the page fault notifications.  Hence we will have ZERO
side effects when no probes are active.

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>

diff --git a/include/asm-i386/kprobes.h b/include/asm-i386/kprobes.h
index 57d157c5cf89a166ca27f6ec1d0bd3896bc47a68..0730a20f6db8100918887179f7924b37bc5fecac 100644 (file)
--- 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 8c0fc227f0fb6934c4f3f7573456d5d21150c6e0..2418a787c4055fb3fb2cd79a43b2e87187b1b162 100644 (file)
--- 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 f466bc804f41ee21a7372cd1cc0328e872629508..2d0af52c823dde7c480bdd92fdc9e1a005482d0c 100644 (file)
--- 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 e9bb26f770eddcfd4288c01d247c5cb9a1a83cd8..15065af566c24924d22a5600b6de5647f2275bb4 100644 (file)
--- 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 98a1e95ddb981c22e84e2d2e82ea754c242f43f7..d36febd9bb183d10c6625e26a79657fa0ae6ec1d 100644 (file)
--- 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 507f26e7ae7cff796f8f7e3a40d7f9b78bb9864e..64aab081153b8345649710623b12704f5a87aec6 100644 (file)
--- 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;
 }