x86: optimize page faults like all other achitectures and kill notifier cruft

x86(-64) are the last architectures still using the page fault notifier
cruft for the kprobes page fault hook.  This patch converts them to the
proper direct calls, and removes the now unused pagefault notifier bits
aswell as the cruft in kprobes.c that was related to this mess.

I know Andi didn't really like this, but all other architecture maintainers
agreed the direct calls are much better and besides the obvious cruft
removal a common way of dealing with kprobes across architectures is
important aswell.

[akpm@linux-foundation.org: build fix]
[akpm@linux-foundation.org: fix sparc64]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: Andi Kleen <ak@suse.de>
Cc: <linux-arch@vger.kernel.org>
Cc: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

20 files changed, 44 insertions, 192 deletions

diff --git a/arch/x86/kernel/kprobes_32.c b/arch/x86/kernel/kprobes_32.c
index e7d0d3c2ef64..06b86e5617f6 100644
--- a/arch/x86/kernel/kprobes_32.c
+++ b/arch/x86/kernel/kprobes_32.c
@@ -584,7 +584,7 @@ out:
         return 1;
 }
 
-static int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
+int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 {
         struct kprobe *cur = kprobe_running();
         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
@@ -666,7 +666,6 @@ int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
                         ret = NOTIFY_STOP;
                 break;
         case DIE_GPF:
-        case DIE_PAGE_FAULT:
                 /* kprobe_running() needs smp_processor_id() */
                 preempt_disable();
                 if (kprobe_running() &&
diff --git a/arch/x86/kernel/kprobes_64.c b/arch/x86/kernel/kprobes_64.c
index 62e28e52d784..7c16506d681f 100644
--- a/arch/x86/kernel/kprobes_64.c
+++ b/arch/x86/kernel/kprobes_64.c
@@ -657,7 +657,6 @@ int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
                         ret = NOTIFY_STOP;
                 break;
         case DIE_GPF:
-        case DIE_PAGE_FAULT:
                 /* kprobe_running() needs smp_processor_id() */
                 preempt_disable();
                 if (kprobe_running() &&
diff --git a/arch/x86/mm/fault_32.c b/arch/x86/mm/fault_32.c
index fcb38e7f3543..be72c2a5b03b 100644
--- a/arch/x86/mm/fault_32.c
+++ b/arch/x86/mm/fault_32.c
@@ -25,6 +25,7 @@
 #include <linux/kprobes.h>
 #include <linux/uaccess.h>
 #include <linux/kdebug.h>
+#include <linux/kprobes.h>
 
 #include <asm/system.h>
 #include <asm/desc.h>
@@ -32,33 +33,27 @@
 
 extern void die(const char *,struct pt_regs *,long);
 
-static ATOMIC_NOTIFIER_HEAD(notify_page_fault_chain);
-
-int register_page_fault_notifier(struct notifier_block *nb)
+#ifdef CONFIG_KPROBES
+static inline int notify_page_fault(struct pt_regs *regs)
 {
-        vmalloc_sync_all();
-        return atomic_notifier_chain_register(&notify_page_fault_chain, nb);
-}
-EXPORT_SYMBOL_GPL(register_page_fault_notifier);
+        int ret = 0;
+
+        /* kprobe_running() needs smp_processor_id() */
+        if (!user_mode_vm(regs)) {
+                preempt_disable();
+                if (kprobe_running() && kprobe_fault_handler(regs, 14))
+                        ret = 1;
+                preempt_enable();
+        }
 
-int unregister_page_fault_notifier(struct notifier_block *nb)
-{
-        return atomic_notifier_chain_unregister(&notify_page_fault_chain, nb);
+        return ret;
 }
-EXPORT_SYMBOL_GPL(unregister_page_fault_notifier);
-
-static inline int notify_page_fault(struct pt_regs *regs, long err)
+#else
+static inline int notify_page_fault(struct pt_regs *regs)
 {
-        struct die_args args = {
-                .regs = regs,
-                .str = "page fault",
-                .err = err,
-                .trapnr = 14,
-                .signr = SIGSEGV
-        };
-        return atomic_notifier_call_chain(&notify_page_fault_chain,
-                                          DIE_PAGE_FAULT, &args);
+        return 0;
 }
+#endif
 
 /*
  * Return EIP plus the CS segment base.  The segment limit is also
@@ -331,7 +326,7 @@ fastcall void __kprobes do_page_fault(struct pt_regs *regs,
         if (unlikely(address >= TASK_SIZE)) {
                 if (!(error_code & 0x0000000d) && vmalloc_fault(address) >= 0)
                         return;
-                if (notify_page_fault(regs, error_code) == NOTIFY_STOP)
+                if (notify_page_fault(regs))
                         return;
                 /*
                  * Don't take the mm semaphore here. If we fixup a prefetch
@@ -340,7 +335,7 @@ fastcall void __kprobes do_page_fault(struct pt_regs *regs,
                 goto bad_area_nosemaphore;
         }
 
-        if (notify_page_fault(regs, error_code) == NOTIFY_STOP)
+        if (notify_page_fault(regs))
                 return;
 
         /* It's safe to allow irq's after cr2 has been saved and the vmalloc
diff --git a/arch/x86/mm/fault_64.c b/arch/x86/mm/fault_64.c
index 54816adb8e93..5e0e54906c48 100644
--- a/arch/x86/mm/fault_64.c
+++ b/arch/x86/mm/fault_64.c
@@ -25,6 +25,7 @@
 #include <linux/kprobes.h>
 #include <linux/uaccess.h>
 #include <linux/kdebug.h>
+#include <linux/kprobes.h>
 
 #include <asm/system.h>
 #include <asm/pgalloc.h>
@@ -40,34 +41,27 @@
 #define PF_RSVD (1<<3)
 #define PF_INSTR        (1<<4)
 
-static ATOMIC_NOTIFIER_HEAD(notify_page_fault_chain);
-
-/* Hook to register for page fault notifications */
-int register_page_fault_notifier(struct notifier_block *nb)
+#ifdef CONFIG_KPROBES
+static inline int notify_page_fault(struct pt_regs *regs)
 {
-        vmalloc_sync_all();
-        return atomic_notifier_chain_register(&notify_page_fault_chain, nb);
-}
-EXPORT_SYMBOL_GPL(register_page_fault_notifier);
+        int ret = 0;
+
+        /* kprobe_running() needs smp_processor_id() */
+        if (!user_mode(regs)) {
+                preempt_disable();
+                if (kprobe_running() && kprobe_fault_handler(regs, 14))
+                        ret = 1;
+                preempt_enable();
+        }
 
-int unregister_page_fault_notifier(struct notifier_block *nb)
-{
-        return atomic_notifier_chain_unregister(&notify_page_fault_chain, nb);
+        return ret;
 }
-EXPORT_SYMBOL_GPL(unregister_page_fault_notifier);
-
-static inline int notify_page_fault(struct pt_regs *regs, long err)
+#else
+static inline int notify_page_fault(struct pt_regs *regs)
 {
-        struct die_args args = {
-                .regs = regs,
-                .str = "page fault",
-                .err = err,
-                .trapnr = 14,
-                .signr = SIGSEGV
-        };
-        return atomic_notifier_call_chain(&notify_page_fault_chain,
-                                          DIE_PAGE_FAULT, &args);
+        return 0;
 }
+#endif
 
 /* Sometimes the CPU reports invalid exceptions on prefetch.
    Check that here and ignore.
@@ -345,7 +339,7 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
                         if (vmalloc_fault(address) >= 0)
                                 return;
                 }
-                if (notify_page_fault(regs, error_code) == NOTIFY_STOP)
+                if (notify_page_fault(regs))
                         return;
                 /*
                  * Don't take the mm semaphore here. If we fixup a prefetch
@@ -354,7 +348,7 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
                 goto bad_area_nosemaphore;
         }
 
-        if (notify_page_fault(regs, error_code) == NOTIFY_STOP)
+        if (notify_page_fault(regs))
                 return;
 
         if (likely(regs->eflags & X86_EFLAGS_IF))
diff --git a/include/asm-avr32/kdebug.h b/include/asm-avr32/kdebug.h
index 7f54e2b15d13..fd7e99046b2f 100644
--- a/include/asm-avr32/kdebug.h
+++ b/include/asm-avr32/kdebug.h
@@ -1,26 +1,10 @@
 #ifndef __ASM_AVR32_KDEBUG_H
 #define __ASM_AVR32_KDEBUG_H
 
-#include <linux/notifier.h>
-
 /* Grossly misnamed. */
 enum die_val {
         DIE_BREAKPOINT,
         DIE_SSTEP,
 };
 
-/*
- * These are only here because kprobes.c wants them to implement a
- * blatant layering violation.  Will hopefully go away soon once all
- * architectures are updated.
- */
-static inline int register_page_fault_notifier(struct notifier_block *nb)
-{
-        return 0;
-}
-static inline int unregister_page_fault_notifier(struct notifier_block *nb)
-{
-        return 0;
-}
-
 #endif /* __ASM_AVR32_KDEBUG_H */
diff --git a/include/asm-avr32/kprobes.h b/include/asm-avr32/kprobes.h
index 190a6377c809..0f3e636e6e4d 100644
--- a/include/asm-avr32/kprobes.h
+++ b/include/asm-avr32/kprobes.h
@@ -17,8 +17,6 @@ typedef u16	kprobe_opcode_t;
 #define BREAKPOINT_INSTRUCTION  0xd673  /* breakpoint */
 #define MAX_INSN_SIZE           2
 
-#define ARCH_INACTIVE_KPROBE_COUNT 1
-
 #define arch_remove_kprobe(p)   do { } while (0)
 
 /* Architecture specific copy of original instruction */
diff --git a/include/asm-ia64/kdebug.h b/include/asm-ia64/kdebug.h
index 320cd8e754ea..35e49407d06c 100644
--- a/include/asm-ia64/kdebug.h
+++ b/include/asm-ia64/kdebug.h
@@ -26,21 +26,6 @@
  * 2005-Oct     Keith Owens <kaos@sgi.com>.  Expand notify_die to cover more
  *              events.
  */
-#include <linux/notifier.h>
-
-/*
- * These are only here because kprobes.c wants them to implement a
- * blatant layering violation.  Will hopefully go away soon once all
- * architectures are updated.
- */
-static inline int register_page_fault_notifier(struct notifier_block *nb)
-{
-        return 0;
-}
-static inline int unregister_page_fault_notifier(struct notifier_block *nb)
-{
-        return 0;
-}
 
 enum die_val {
         DIE_BREAK = 1,
diff --git a/include/asm-ia64/kprobes.h b/include/asm-ia64/kprobes.h
index 067d9dea68f9..6c79edf24d73 100644
--- a/include/asm-ia64/kprobes.h
+++ b/include/asm-ia64/kprobes.h
@@ -83,7 +83,6 @@ struct kprobe_ctlblk {
 };
 
 #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/kdebug.h b/include/asm-powerpc/kdebug.h
index 295f0162c608..ae6d206728af 100644
--- a/include/asm-powerpc/kdebug.h
+++ b/include/asm-powerpc/kdebug.h
@@ -2,25 +2,6 @@
 #define _ASM_POWERPC_KDEBUG_H
 #ifdef __KERNEL__
 
-/* nearly identical to x86_64/i386 code */
-
-#include <linux/notifier.h>
-
-/*
- * These are only here because kprobes.c wants them to implement a
- * blatant layering violation.  Will hopefully go away soon once all
- * architectures are updated.
- */
-static inline int register_page_fault_notifier(struct notifier_block *nb)
-{
-        return 0;
-}
-static inline int unregister_page_fault_notifier(struct notifier_block *nb)
-{
-        return 0;
-}
-extern struct atomic_notifier_head powerpc_die_chain;
-
 /* Grossly misnamed. */
 enum die_val {
         DIE_OOPS = 1,
diff --git a/include/asm-powerpc/kprobes.h b/include/asm-powerpc/kprobes.h
index 8b08b447d6f3..c16973d5de62 100644
--- a/include/asm-powerpc/kprobes.h
+++ b/include/asm-powerpc/kprobes.h
@@ -81,7 +81,6 @@ typedef unsigned int kprobe_opcode_t;
 #endif
 
 #define ARCH_SUPPORTS_KRETPROBES
-#define  ARCH_INACTIVE_KPROBE_COUNT 1
 #define flush_insn_slot(p)      do { } while (0)
 
 void kretprobe_trampoline(void);
diff --git a/include/asm-s390/kdebug.h b/include/asm-s390/kdebug.h
index 04418af08f85..40db27cd6e60 100644
--- a/include/asm-s390/kdebug.h
+++ b/include/asm-s390/kdebug.h
@@ -4,24 +4,9 @@
 /*
  * Feb 2006 Ported to s390 <grundym@us.ibm.com>
  */
-#include <linux/notifier.h>
 
 struct pt_regs;
 
-/*
- * These are only here because kprobes.c wants them to implement a
- * blatant layering violation. Will hopefully go away soon once all
- * architectures are updated.
- */
-static inline int register_page_fault_notifier(struct notifier_block *nb)
-{
-        return 0;
-}
-static inline int unregister_page_fault_notifier(struct notifier_block *nb)
-{
-        return 0;
-}
-
 enum die_val {
         DIE_OOPS = 1,
         DIE_BPT,
diff --git a/include/asm-s390/kprobes.h b/include/asm-s390/kprobes.h
index 340ba10446ea..8bc67cc9ffd2 100644
--- a/include/asm-s390/kprobes.h
+++ b/include/asm-s390/kprobes.h
@@ -47,7 +47,6 @@ typedef u16 kprobe_opcode_t;
         : (((unsigned long)current_thread_info()) + THREAD_SIZE - (ADDR)))
 
 #define ARCH_SUPPORTS_KRETPROBES
-#define ARCH_INACTIVE_KPROBE_COUNT 0
 
 #define KPROBE_SWAP_INST        0x10
 
diff --git a/include/asm-sh/kdebug.h b/include/asm-sh/kdebug.h
index 382cfc7deb73..49cd69051a88 100644
--- a/include/asm-sh/kdebug.h
+++ b/include/asm-sh/kdebug.h
@@ -1,8 +1,6 @@
 #ifndef __ASM_SH_KDEBUG_H
 #define __ASM_SH_KDEBUG_H
 
-#include <linux/notifier.h>
-
 /* Grossly misnamed. */
 enum die_val {
         DIE_TRAP,
diff --git a/include/asm-sparc64/kdebug.h b/include/asm-sparc64/kdebug.h
index 9974c7b0aebc..f905b773235a 100644
--- a/include/asm-sparc64/kdebug.h
+++ b/include/asm-sparc64/kdebug.h
@@ -1,26 +1,8 @@
 #ifndef _SPARC64_KDEBUG_H
 #define _SPARC64_KDEBUG_H
 
-/* Nearly identical to x86_64/i386 code. */
-
-#include <linux/notifier.h>
-
 struct pt_regs;
 
-/*
- * These are only here because kprobes.c wants them to implement a
- * blatant layering violation.  Will hopefully go away soon once all
- * architectures are updated.
- */
-static inline int register_page_fault_notifier(struct notifier_block *nb)
-{
-        return 0;
-}
-static inline int unregister_page_fault_notifier(struct notifier_block *nb)
-{
-        return 0;
-}
-
 extern void bad_trap(struct pt_regs *, long);
 
 /* Grossly misnamed. */
diff --git a/include/asm-sparc64/kprobes.h b/include/asm-sparc64/kprobes.h
index 7f6774dca5f4..a04145b77f96 100644
--- a/include/asm-sparc64/kprobes.h
+++ b/include/asm-sparc64/kprobes.h
@@ -11,7 +11,6 @@ typedef u32 kprobe_opcode_t;
 #define MAX_INSN_SIZE 2
 
 #define arch_remove_kprobe(p)   do {} while (0)
-#define  ARCH_INACTIVE_KPROBE_COUNT 0
 
 #define flush_insn_slot(p)              \
 do {    flushi(&(p)->ainsn.insn[0]);    \
diff --git a/include/asm-x86/kdebug_32.h b/include/asm-x86/kdebug_32.h
index a185b5f73e7f..181d437eef4b 100644
--- a/include/asm-x86/kdebug_32.h
+++ b/include/asm-x86/kdebug_32.h
@@ -5,14 +5,9 @@
  * Aug-05 2004 Ported by Prasanna S Panchamukhi <prasanna@in.ibm.com>
  * from x86_64 architecture.
  */
-#include <linux/notifier.h>
 
 struct pt_regs;
 
-extern int register_page_fault_notifier(struct notifier_block *);
-extern int unregister_page_fault_notifier(struct notifier_block *);
-
-
 /* Grossly misnamed. */
 enum die_val {
         DIE_OOPS = 1,
@@ -27,7 +22,6 @@ enum die_val {
         DIE_GPF,
         DIE_CALL,
         DIE_NMI_IPI,
-        DIE_PAGE_FAULT,
 };
 
 #endif
diff --git a/include/asm-x86/kdebug_64.h b/include/asm-x86/kdebug_64.h
index d7e2bcf49e4f..df413e05375e 100644
--- a/include/asm-x86/kdebug_64.h
+++ b/include/asm-x86/kdebug_64.h
@@ -1,13 +1,10 @@
 #ifndef _X86_64_KDEBUG_H
 #define _X86_64_KDEBUG_H 1
 
-#include <linux/notifier.h>
+#include <linux/compiler.h>
 
 struct pt_regs;
 
-extern int register_page_fault_notifier(struct notifier_block *);
-extern int unregister_page_fault_notifier(struct notifier_block *);
-
 /* Grossly misnamed. */
 enum die_val {
         DIE_OOPS = 1,
@@ -22,7 +19,6 @@ enum die_val {
         DIE_GPF,
         DIE_CALL,
         DIE_NMI_IPI,
-        DIE_PAGE_FAULT,
 };
 
 extern void printk_address(unsigned long address);
diff --git a/include/asm-x86/kprobes_32.h b/include/asm-x86/kprobes_32.h
index 06f7303c30ca..f2489d07ce88 100644
--- a/include/asm-x86/kprobes_32.h
+++ b/include/asm-x86/kprobes_32.h
@@ -43,7 +43,6 @@ typedef u8 kprobe_opcode_t;
         : (((unsigned long)current_thread_info()) + THREAD_SIZE - (ADDR)))
 
 #define ARCH_SUPPORTS_KRETPROBES
-#define  ARCH_INACTIVE_KPROBE_COUNT 0
 #define flush_insn_slot(p)      do { } while (0)
 
 void arch_remove_kprobe(struct kprobe *p);
@@ -89,4 +88,5 @@ static inline void restore_interrupts(struct pt_regs *regs)
 
 extern int kprobe_exceptions_notify(struct notifier_block *self,
                                     unsigned long val, void *data);
+extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
 #endif                          /* _ASM_KPROBES_H */
diff --git a/include/asm-x86/kprobes_64.h b/include/asm-x86/kprobes_64.h
index 7db825403e01..3f495e5308b1 100644
--- a/include/asm-x86/kprobes_64.h
+++ b/include/asm-x86/kprobes_64.h
@@ -42,7 +42,6 @@ typedef u8 kprobe_opcode_t;
         : (((unsigned long)current_thread_info()) + THREAD_SIZE - (ADDR)))
 
 #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 4b8a4493c541..f9798ff7899f 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -64,7 +64,6 @@
 
 static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
 static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
-static atomic_t kprobe_count;
 
 /* NOTE: change this value only with kprobe_mutex held */
 static bool kprobe_enabled;
@@ -73,11 +72,6 @@ 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
@@ -556,8 +550,6 @@ 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;
         }
 
@@ -569,13 +561,9 @@ static int __kprobes __register_kprobe(struct kprobe *p,
         hlist_add_head_rcu(&p->hlist,
                        &kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);
 
-        if (kprobe_enabled) {
-                if (atomic_add_return(1, &kprobe_count) == \
-                                (ARCH_INACTIVE_KPROBE_COUNT + 1))
-                        register_page_fault_notifier(&kprobe_page_fault_nb);
-
+        if (kprobe_enabled)
                 arch_arm_kprobe(p);
-        }
+
 out:
         mutex_unlock(&kprobe_mutex);
 
@@ -658,16 +646,6 @@ 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 = {
@@ -815,7 +793,6 @@ static int __init init_kprobes(void)
                 INIT_HLIST_HEAD(&kprobe_table[i]);
                 INIT_HLIST_HEAD(&kretprobe_inst_table[i]);
         }
-        atomic_set(&kprobe_count, 0);
 
         /* By default, kprobes are enabled */
         kprobe_enabled = true;
@@ -921,13 +898,6 @@ static void __kprobes enable_all_kprobes(void)
         if (kprobe_enabled)
                 goto already_enabled;
 
-        /*
-         * Re-register the page fault notifier only if there are any
-         * active probes at the time of enabling kprobes globally
-         */
-        if (atomic_read(&kprobe_count) > ARCH_INACTIVE_KPROBE_COUNT)
-                register_page_fault_notifier(&kprobe_page_fault_nb);
-
         for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
                 head = &kprobe_table[i];
                 hlist_for_each_entry_rcu(p, node, head, hlist)
@@ -968,10 +938,7 @@ static void __kprobes disable_all_kprobes(void)
         mutex_unlock(&kprobe_mutex);
         /* Allow all currently running kprobes to complete */
         synchronize_sched();
-
-        mutex_lock(&kprobe_mutex);
-        /* Unconditionally unregister the page_fault notifier */
-        unregister_page_fault_notifier(&kprobe_page_fault_nb);
+        return;
 
 already_disabled:
         mutex_unlock(&kprobe_mutex);