Merge tag 'trace-v5.16' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing updates from Steven Rostedt:

 - kprobes: Restructured stack unwinder to show properly on x86 when a
   stack dump happens from a kretprobe callback.

 - Fix to bootconfig parsing

 - Have tracefs allow owner and group permissions by default (only
   denying others). There's been pressure to allow non root to tracefs
   in a controlled fashion, and using groups is probably the safest.

 - Bootconfig memory managament updates.

 - Bootconfig clean up to have the tools directory be less dependent on
   changes in the kernel tree.

 - Allow perf to be traced by function tracer.

 - Rewrite of function graph tracer to be a callback from the function
   tracer instead of having its own trampoline (this change will happen
   on an arch by arch basis, and currently only x86_64 implements it).

 - Allow multiple direct trampolines (bpf hooks to functions) be batched
   together in one synchronization.

 - Allow histogram triggers to add variables that can perform
   calculations against the event's fields.

 - Use the linker to determine architecture callbacks from the ftrace
   trampoline to allow for proper parameter prototypes and prevent
   warnings from the compiler.

 - Extend histogram triggers to key off of variables.

 - Have trace recursion use bit magic to determine preempt context over
   if branches.

 - Have trace recursion disable preemption as all use cases do anyway.

 - Added testing for verification of tracing utilities.

 - Various small clean ups and fixes.

* tag 'trace-v5.16' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: (101 commits)
  tracing/histogram: Fix semicolon.cocci warnings
  tracing/histogram: Fix documentation inline emphasis warning
  tracing: Increase PERF_MAX_TRACE_SIZE to handle Sentinel1 and docker together
  tracing: Show size of requested perf buffer
  bootconfig: Initialize ret in xbc_parse_tree()
  ftrace: do CPU checking after preemption disabled
  ftrace: disable preemption when recursion locked
  tracing/histogram: Document expression arithmetic and constants
  tracing/histogram: Optimize division by a power of 2
  tracing/histogram: Covert expr to const if both operands are constants
  tracing/histogram: Simplify handling of .sym-offset in expressions
  tracing: Fix operator precedence for hist triggers expression
  tracing: Add division and multiplication support for hist triggers
  tracing: Add support for creating hist trigger variables from literal
  selftests/ftrace: Stop tracing while reading the trace file by default
  MAINTAINERS: Update KPROBES and TRACING entries
  test_kprobes: Move it from kernel/ to lib/
  docs, kprobes: Remove invalid URL and add new reference
  samples/kretprobes: Fix return value if register_kretprobe() failed
  lib/bootconfig: Fix the xbc_get_info kerneldoc
  ...

1 files changed, 280 insertions, 227 deletions

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 9a38e7581a5c..e9db0c810554 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1,7 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  *  Kernel Probes (KProbes)
- *  kernel/kprobes.c
  *
  * Copyright (C) IBM Corporation, 2002, 2004
  *
@@ -18,6 +17,9 @@
  *		<jkenisto@us.ibm.com> and Prasanna S Panchamukhi
  *		<prasanna@in.ibm.com> added function-return probes.
  */
+
+#define pr_fmt(fmt) "kprobes: " fmt
+
 #include <linux/kprobes.h>
 #include <linux/hash.h>
 #include <linux/init.h>
@@ -49,18 +51,18 @@
 
 static int kprobes_initialized;
 /* kprobe_table can be accessed by
- * - Normal hlist traversal and RCU add/del under kprobe_mutex is held.
+ * - Normal hlist traversal and RCU add/del under 'kprobe_mutex' is held.
  * Or
  * - RCU hlist traversal under disabling preempt (breakpoint handlers)
  */
 static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
 
-/* NOTE: change this value only with kprobe_mutex held */
+/* NOTE: change this value only with 'kprobe_mutex' held */
 static bool kprobes_all_disarmed;
 
-/* This protects kprobe_table and optimizing_list */
+/* This protects 'kprobe_table' and 'optimizing_list' */
 static DEFINE_MUTEX(kprobe_mutex);
-static DEFINE_PER_CPU(struct kprobe *, kprobe_instance) = NULL;
+static DEFINE_PER_CPU(struct kprobe *, kprobe_instance);
 
 kprobe_opcode_t * __weak kprobe_lookup_name(const char *name,
 					unsigned int __unused)
@@ -68,12 +70,15 @@ kprobe_opcode_t * __weak kprobe_lookup_name(const char *name,
 	return ((kprobe_opcode_t *)(kallsyms_lookup_name(name)));
 }
 
-/* Blacklist -- list of struct kprobe_blacklist_entry */
+/*
+ * Blacklist -- list of 'struct kprobe_blacklist_entry' to store info where
+ * kprobes can not probe.
+ */
 static LIST_HEAD(kprobe_blacklist);
 
 #ifdef __ARCH_WANT_KPROBES_INSN_SLOT
 /*
- * kprobe->ainsn.insn points to the copy of the instruction to be
+ * 'kprobe::ainsn.insn' points to the copy of the instruction to be
  * single-stepped. x86_64, POWER4 and above have no-exec support and
  * stepping on the instruction on a vmalloced/kmalloced/data page
  * is a recipe for disaster
@@ -104,6 +109,12 @@ enum kprobe_slot_state {
 
 void __weak *alloc_insn_page(void)
 {
+	/*
+	 * Use module_alloc() so this page is within +/- 2GB of where the
+	 * kernel image and loaded module images reside. This is required
+	 * for most of the architectures.
+	 * (e.g. x86-64 needs this to handle the %rip-relative fixups.)
+	 */
 	return module_alloc(PAGE_SIZE);
 }
 
@@ -139,6 +150,7 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c)
 	list_for_each_entry_rcu(kip, &c->pages, list) {
 		if (kip->nused < slots_per_page(c)) {
 			int i;
+
 			for (i = 0; i < slots_per_page(c); i++) {
 				if (kip->slot_used[i] == SLOT_CLEAN) {
 					kip->slot_used[i] = SLOT_USED;
@@ -164,11 +176,6 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c)
 	if (!kip)
 		goto out;
 
-	/*
-	 * Use module_alloc so this page is within +/- 2GB of where the
-	 * kernel image and loaded module images reside. This is required
-	 * so x86_64 can correctly handle the %rip-relative fixups.
-	 */
 	kip->insns = c->alloc();
 	if (!kip->insns) {
 		kfree(kip);
@@ -191,8 +198,8 @@ out:
 	return slot;
 }
 
-/* Return 1 if all garbages are collected, otherwise 0. */
-static int collect_one_slot(struct kprobe_insn_page *kip, int idx)
+/* Return true if all garbages are collected, otherwise false. */
+static bool collect_one_slot(struct kprobe_insn_page *kip, int idx)
 {
 	kip->slot_used[idx] = SLOT_CLEAN;
 	kip->nused--;
@@ -216,9 +223,9 @@ static int collect_one_slot(struct kprobe_insn_page *kip, int idx)
 			kip->cache->free(kip->insns);
 			kfree(kip);
 		}
-		return 1;
+		return true;
 	}
-	return 0;
+	return false;
 }
 
 static int collect_garbage_slots(struct kprobe_insn_cache *c)
@@ -230,6 +237,7 @@ static int collect_garbage_slots(struct kprobe_insn_cache *c)
 
 	list_for_each_entry_safe(kip, next, &c->pages, list) {
 		int i;
+
 		if (kip->ngarbage == 0)
 			continue;
 		kip->ngarbage = 0;	/* we will collect all garbages */
@@ -310,7 +318,7 @@ int kprobe_cache_get_kallsym(struct kprobe_insn_cache *c, unsigned int *symnum,
 	list_for_each_entry_rcu(kip, &c->pages, list) {
 		if ((*symnum)--)
 			continue;
-		strlcpy(sym, c->sym, KSYM_NAME_LEN);
+		strscpy(sym, c->sym, KSYM_NAME_LEN);
 		*type = 't';
 		*value = (unsigned long)kip->insns;
 		ret = 0;
@@ -358,9 +366,9 @@ static inline void reset_kprobe_instance(void)
 
 /*
  * This routine is called either:
- * 	- under the kprobe_mutex - during kprobe_[un]register()
- * 				OR
- * 	- with preemption disabled - from arch/xxx/kernel/kprobes.c
+ *	- under the 'kprobe_mutex' - during kprobe_[un]register().
+ *				OR
+ *	- with preemption disabled - from architecture specific code.
  */
 struct kprobe *get_kprobe(void *addr)
 {
@@ -380,22 +388,20 @@ NOKPROBE_SYMBOL(get_kprobe);
 
 static int aggr_pre_handler(struct kprobe *p, struct pt_regs *regs);
 
-/* Return true if the kprobe is an aggregator */
-static inline int kprobe_aggrprobe(struct kprobe *p)
+/* Return true if 'p' is an aggregator */
+static inline bool kprobe_aggrprobe(struct kprobe *p)
 {
 	return p->pre_handler == aggr_pre_handler;
 }
 
-/* Return true(!0) if the kprobe is unused */
-static inline int kprobe_unused(struct kprobe *p)
+/* Return true if 'p' is unused */
+static inline bool kprobe_unused(struct kprobe *p)
 {
 	return kprobe_aggrprobe(p) && kprobe_disabled(p) &&
 	       list_empty(&p->list);
 }
 
-/*
- * Keep all fields in the kprobe consistent
- */
+/* Keep all fields in the kprobe consistent. */
 static inline void copy_kprobe(struct kprobe *ap, struct kprobe *p)
 {
 	memcpy(&p->opcode, &ap->opcode, sizeof(kprobe_opcode_t));
@@ -403,11 +409,11 @@ static inline void copy_kprobe(struct kprobe *ap, struct kprobe *p)
 }
 
 #ifdef CONFIG_OPTPROBES
-/* NOTE: change this value only with kprobe_mutex held */
+/* NOTE: This is protected by 'kprobe_mutex'. */
 static bool kprobes_allow_optimization;
 
 /*
- * Call all pre_handler on the list, but ignores its return value.
+ * Call all 'kprobe::pre_handler' on the list, but ignores its return value.
  * This must be called from arch-dep optimized caller.
  */
 void opt_pre_handler(struct kprobe *p, struct pt_regs *regs)
@@ -435,7 +441,7 @@ static void free_aggr_kprobe(struct kprobe *p)
 	kfree(op);
 }
 
-/* Return true(!0) if the kprobe is ready for optimization. */
+/* Return true if the kprobe is ready for optimization. */
 static inline int kprobe_optready(struct kprobe *p)
 {
 	struct optimized_kprobe *op;
@@ -448,8 +454,8 @@ static inline int kprobe_optready(struct kprobe *p)
 	return 0;
 }
 
-/* Return true(!0) if the kprobe is disarmed. Note: p must be on hash list */
-static inline int kprobe_disarmed(struct kprobe *p)
+/* Return true if the kprobe is disarmed. Note: p must be on hash list */
+static inline bool kprobe_disarmed(struct kprobe *p)
 {
 	struct optimized_kprobe *op;
 
@@ -462,32 +468,32 @@ static inline int kprobe_disarmed(struct kprobe *p)
 	return kprobe_disabled(p) && list_empty(&op->list);
 }
 
-/* Return true(!0) if the probe is queued on (un)optimizing lists */
-static int kprobe_queued(struct kprobe *p)
+/* Return true if the probe is queued on (un)optimizing lists */
+static bool kprobe_queued(struct kprobe *p)
 {
 	struct optimized_kprobe *op;
 
 	if (kprobe_aggrprobe(p)) {
 		op = container_of(p, struct optimized_kprobe, kp);
 		if (!list_empty(&op->list))
-			return 1;
+			return true;
 	}
-	return 0;
+	return false;
 }
 
 /*
  * Return an optimized kprobe whose optimizing code replaces
- * instructions including addr (exclude breakpoint).
+ * instructions including 'addr' (exclude breakpoint).
  */
-static struct kprobe *get_optimized_kprobe(unsigned long addr)
+static struct kprobe *get_optimized_kprobe(kprobe_opcode_t *addr)
 {
 	int i;
 	struct kprobe *p = NULL;
 	struct optimized_kprobe *op;
 
 	/* Don't check i == 0, since that is a breakpoint case. */
-	for (i = 1; !p && i < MAX_OPTIMIZED_LENGTH; i++)
-		p = get_kprobe((void *)(addr - i));
+	for (i = 1; !p && i < MAX_OPTIMIZED_LENGTH / sizeof(kprobe_opcode_t); i++)
+		p = get_kprobe(addr - i);
 
 	if (p && kprobe_optready(p)) {
 		op = container_of(p, struct optimized_kprobe, kp);
@@ -498,7 +504,7 @@ static struct kprobe *get_optimized_kprobe(unsigned long addr)
 	return NULL;
 }
 
-/* Optimization staging list, protected by kprobe_mutex */
+/* Optimization staging list, protected by 'kprobe_mutex' */
 static LIST_HEAD(optimizing_list);
 static LIST_HEAD(unoptimizing_list);
 static LIST_HEAD(freeing_list);
@@ -509,20 +515,20 @@ static DECLARE_DELAYED_WORK(optimizing_work, kprobe_optimizer);
 
 /*
  * Optimize (replace a breakpoint with a jump) kprobes listed on
- * optimizing_list.
+ * 'optimizing_list'.
  */
 static void do_optimize_kprobes(void)
 {
 	lockdep_assert_held(&text_mutex);
 	/*
-	 * The optimization/unoptimization refers online_cpus via
-	 * stop_machine() and cpu-hotplug modifies online_cpus.
-	 * And same time, text_mutex will be held in cpu-hotplug and here.
-	 * This combination can cause a deadlock (cpu-hotplug try to lock
-	 * text_mutex but stop_machine can not be done because online_cpus
-	 * has been changed)
-	 * To avoid this deadlock, caller must have locked cpu hotplug
-	 * for preventing cpu-hotplug outside of text_mutex locking.
+	 * The optimization/unoptimization refers 'online_cpus' via
+	 * stop_machine() and cpu-hotplug modifies the 'online_cpus'.
+	 * And same time, 'text_mutex' will be held in cpu-hotplug and here.
+	 * This combination can cause a deadlock (cpu-hotplug tries to lock
+	 * 'text_mutex' but stop_machine() can not be done because
+	 * the 'online_cpus' has been changed)
+	 * To avoid this deadlock, caller must have locked cpu-hotplug
+	 * for preventing cpu-hotplug outside of 'text_mutex' locking.
 	 */
 	lockdep_assert_cpus_held();
 
@@ -536,7 +542,7 @@ static void do_optimize_kprobes(void)
 
 /*
  * Unoptimize (replace a jump with a breakpoint and remove the breakpoint
- * if need) kprobes listed on unoptimizing_list.
+ * if need) kprobes listed on 'unoptimizing_list'.
  */
 static void do_unoptimize_kprobes(void)
 {
@@ -551,7 +557,7 @@ static void do_unoptimize_kprobes(void)
 		return;
 
 	arch_unoptimize_kprobes(&unoptimizing_list, &freeing_list);
-	/* Loop free_list for disarming */
+	/* Loop on 'freeing_list' for disarming */
 	list_for_each_entry_safe(op, tmp, &freeing_list, list) {
 		/* Switching from detour code to origin */
 		op->kp.flags &= ~KPROBE_FLAG_OPTIMIZED;
@@ -562,7 +568,7 @@ static void do_unoptimize_kprobes(void)
 			/*
 			 * Remove unused probes from hash list. After waiting
 			 * for synchronization, these probes are reclaimed.
-			 * (reclaiming is done by do_free_cleaned_kprobes.)
+			 * (reclaiming is done by do_free_cleaned_kprobes().)
 			 */
 			hlist_del_rcu(&op->kp.hlist);
 		} else
@@ -570,7 +576,7 @@ static void do_unoptimize_kprobes(void)
 	}
 }
 
-/* Reclaim all kprobes on the free_list */
+/* Reclaim all kprobes on the 'freeing_list' */
 static void do_free_cleaned_kprobes(void)
 {
 	struct optimized_kprobe *op, *tmp;
@@ -642,9 +648,9 @@ void wait_for_kprobe_optimizer(void)
 	while (!list_empty(&optimizing_list) || !list_empty(&unoptimizing_list)) {
 		mutex_unlock(&kprobe_mutex);
 
-		/* this will also make optimizing_work execute immmediately */
+		/* This will also make 'optimizing_work' execute immmediately */
 		flush_delayed_work(&optimizing_work);
-		/* @optimizing_work might not have been queued yet, relax */
+		/* 'optimizing_work' might not have been queued yet, relax */
 		cpu_relax();
 
 		mutex_lock(&kprobe_mutex);
@@ -675,7 +681,7 @@ static void optimize_kprobe(struct kprobe *p)
 	    (kprobe_disabled(p) || kprobes_all_disarmed))
 		return;
 
-	/* kprobes with post_handler can not be optimized */
+	/* kprobes with 'post_handler' can not be optimized */
 	if (p->post_handler)
 		return;
 
@@ -695,7 +701,10 @@ static void optimize_kprobe(struct kprobe *p)
 	}
 	op->kp.flags |= KPROBE_FLAG_OPTIMIZED;
 
-	/* On unoptimizing/optimizing_list, op must have OPTIMIZED flag */
+	/*
+	 * On the 'unoptimizing_list' and 'optimizing_list',
+	 * 'op' must have OPTIMIZED flag
+	 */
 	if (WARN_ON_ONCE(!list_empty(&op->list)))
 		return;
 
@@ -765,7 +774,7 @@ static int reuse_unused_kprobe(struct kprobe *ap)
 	WARN_ON_ONCE(list_empty(&op->list));
 	/* Enable the probe again */
 	ap->flags &= ~KPROBE_FLAG_DISABLED;
-	/* Optimize it again (remove from op->list) */
+	/* Optimize it again. (remove from 'op->list') */
 	if (!kprobe_optready(ap))
 		return -EINVAL;
 
@@ -815,7 +824,7 @@ static void prepare_optimized_kprobe(struct kprobe *p)
 	__prepare_optimized_kprobe(op, p);
 }
 
-/* Allocate new optimized_kprobe and try to prepare optimized instructions */
+/* Allocate new optimized_kprobe and try to prepare optimized instructions. */
 static struct kprobe *alloc_aggr_kprobe(struct kprobe *p)
 {
 	struct optimized_kprobe *op;
@@ -834,19 +843,19 @@ static struct kprobe *alloc_aggr_kprobe(struct kprobe *p)
 static void init_aggr_kprobe(struct kprobe *ap, struct kprobe *p);
 
 /*
- * Prepare an optimized_kprobe and optimize it
- * NOTE: p must be a normal registered kprobe
+ * Prepare an optimized_kprobe and optimize it.
+ * NOTE: 'p' must be a normal registered kprobe.
  */
 static void try_to_optimize_kprobe(struct kprobe *p)
 {
 	struct kprobe *ap;
 	struct optimized_kprobe *op;
 
-	/* Impossible to optimize ftrace-based kprobe */
+	/* Impossible to optimize ftrace-based kprobe. */
 	if (kprobe_ftrace(p))
 		return;
 
-	/* For preparing optimization, jump_label_text_reserved() is called */
+	/* For preparing optimization, jump_label_text_reserved() is called. */
 	cpus_read_lock();
 	jump_label_lock();
 	mutex_lock(&text_mutex);
@@ -857,14 +866,14 @@ static void try_to_optimize_kprobe(struct kprobe *p)
 
 	op = container_of(ap, struct optimized_kprobe, kp);
 	if (!arch_prepared_optinsn(&op->optinsn)) {
-		/* If failed to setup optimizing, fallback to kprobe */
+		/* If failed to setup optimizing, fallback to kprobe. */
 		arch_remove_optimized_kprobe(op);
 		kfree(op);
 		goto out;
 	}
 
 	init_aggr_kprobe(ap, p);
-	optimize_kprobe(ap);	/* This just kicks optimizer thread */
+	optimize_kprobe(ap);	/* This just kicks optimizer thread. */
 
 out:
 	mutex_unlock(&text_mutex);
@@ -879,7 +888,7 @@ static void optimize_all_kprobes(void)
 	unsigned int i;
 
 	mutex_lock(&kprobe_mutex);
-	/* If optimization is already allowed, just return */
+	/* If optimization is already allowed, just return. */
 	if (kprobes_allow_optimization)
 		goto out;
 
@@ -892,7 +901,7 @@ static void optimize_all_kprobes(void)
 				optimize_kprobe(p);
 	}
 	cpus_read_unlock();
-	printk(KERN_INFO "Kprobes globally optimized\n");
+	pr_info("kprobe jump-optimization is enabled. All kprobes are optimized if possible.\n");
 out:
 	mutex_unlock(&kprobe_mutex);
 }
@@ -905,7 +914,7 @@ static void unoptimize_all_kprobes(void)
 	unsigned int i;
 
 	mutex_lock(&kprobe_mutex);
-	/* If optimization is already prohibited, just return */
+	/* If optimization is already prohibited, just return. */
 	if (!kprobes_allow_optimization) {
 		mutex_unlock(&kprobe_mutex);
 		return;
@@ -923,9 +932,9 @@ static void unoptimize_all_kprobes(void)
 	cpus_read_unlock();
 	mutex_unlock(&kprobe_mutex);
 
-	/* Wait for unoptimizing completion */
+	/* Wait for unoptimizing completion. */
 	wait_for_kprobe_optimizer();
-	printk(KERN_INFO "Kprobes globally unoptimized\n");
+	pr_info("kprobe jump-optimization is disabled. All kprobes are based on software breakpoint.\n");
 }
 
 static DEFINE_MUTEX(kprobe_sysctl_mutex);
@@ -950,13 +959,15 @@ int proc_kprobes_optimization_handler(struct ctl_table *table, int write,
 }
 #endif /* CONFIG_SYSCTL */
 
-/* Put a breakpoint for a probe. Must be called with text_mutex locked */
+/* Put a breakpoint for a probe. */
 static void __arm_kprobe(struct kprobe *p)
 {
 	struct kprobe *_p;
 
-	/* Check collision with other optimized kprobes */
-	_p = get_optimized_kprobe((unsigned long)p->addr);
+	lockdep_assert_held(&text_mutex);
+
+	/* Find the overlapping optimized kprobes. */
+	_p = get_optimized_kprobe(p->addr);
 	if (unlikely(_p))
 		/* Fallback to unoptimized kprobe */
 		unoptimize_kprobe(_p, true);
@@ -965,22 +976,29 @@ static void __arm_kprobe(struct kprobe *p)
 	optimize_kprobe(p);	/* Try to optimize (add kprobe to a list) */
 }
 
-/* Remove the breakpoint of a probe. Must be called with text_mutex locked */
+/* Remove the breakpoint of a probe. */
 static void __disarm_kprobe(struct kprobe *p, bool reopt)
 {
 	struct kprobe *_p;
 
+	lockdep_assert_held(&text_mutex);
+
 	/* Try to unoptimize */
 	unoptimize_kprobe(p, kprobes_all_disarmed);
 
 	if (!kprobe_queued(p)) {
 		arch_disarm_kprobe(p);
-		/* If another kprobe was blocked, optimize it. */
-		_p = get_optimized_kprobe((unsigned long)p->addr);
+		/* If another kprobe was blocked, re-optimize it. */
+		_p = get_optimized_kprobe(p->addr);
 		if (unlikely(_p) && reopt)
 			optimize_kprobe(_p);
 	}
-	/* TODO: reoptimize others after unoptimized this probe */
+	/*
+	 * TODO: Since unoptimization and real disarming will be done by
+	 * the worker thread, we can not check whether another probe are
+	 * unoptimized because of this probe here. It should be re-optimized
+	 * by the worker thread.
+	 */
 }
 
 #else /* !CONFIG_OPTPROBES */
@@ -1003,7 +1021,7 @@ static int reuse_unused_kprobe(struct kprobe *ap)
 	 * unregistered.
 	 * Thus there should be no chance to reuse unused kprobe.
 	 */
-	printk(KERN_ERR "Error: There should be no unused kprobe here.\n");
+	WARN_ON_ONCE(1);
 	return -EINVAL;
 }
 
@@ -1033,34 +1051,21 @@ static struct ftrace_ops kprobe_ipmodify_ops __read_mostly = {
 static int kprobe_ipmodify_enabled;
 static int kprobe_ftrace_enabled;
 
-/* Must ensure p->addr is really on ftrace */
-static int prepare_kprobe(struct kprobe *p)
-{
-	if (!kprobe_ftrace(p))
-		return arch_prepare_kprobe(p);
-
-	return arch_prepare_kprobe_ftrace(p);
-}
-
-/* Caller must lock kprobe_mutex */
 static int __arm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
 			       int *cnt)
 {
 	int ret = 0;
 
+	lockdep_assert_held(&kprobe_mutex);
+
 	ret = ftrace_set_filter_ip(ops, (unsigned long)p->addr, 0, 0);
-	if (ret) {
-		pr_debug("Failed to arm kprobe-ftrace at %pS (%d)\n",
-			 p->addr, ret);
+	if (WARN_ONCE(ret < 0, "Failed to arm kprobe-ftrace at %pS (error %d)\n", p->addr, ret))
 		return ret;
-	}
 
 	if (*cnt == 0) {
 		ret = register_ftrace_function(ops);
-		if (ret) {
-			pr_debug("Failed to init kprobe-ftrace (%d)\n", ret);
+		if (WARN(ret < 0, "Failed to register kprobe-ftrace (error %d)\n", ret))
 			goto err_ftrace;
-		}
 	}
 
 	(*cnt)++;
@@ -1084,22 +1089,23 @@ static int arm_kprobe_ftrace(struct kprobe *p)
 		ipmodify ? &kprobe_ipmodify_enabled : &kprobe_ftrace_enabled);
 }
 
-/* Caller must lock kprobe_mutex */
 static int __disarm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
 				  int *cnt)
 {
 	int ret = 0;
 
+	lockdep_assert_held(&kprobe_mutex);
+
 	if (*cnt == 1) {
 		ret = unregister_ftrace_function(ops);
-		if (WARN(ret < 0, "Failed to unregister kprobe-ftrace (%d)\n", ret))
+		if (WARN(ret < 0, "Failed to unregister kprobe-ftrace (error %d)\n", ret))
 			return ret;
 	}
 
 	(*cnt)--;
 
 	ret = ftrace_set_filter_ip(ops, (unsigned long)p->addr, 1, 0);
-	WARN_ONCE(ret < 0, "Failed to disarm kprobe-ftrace at %pS (%d)\n",
+	WARN_ONCE(ret < 0, "Failed to disarm kprobe-ftrace at %pS (error %d)\n",
 		  p->addr, ret);
 	return ret;
 }
@@ -1113,11 +1119,6 @@ static int disarm_kprobe_ftrace(struct kprobe *p)
 		ipmodify ? &kprobe_ipmodify_enabled : &kprobe_ftrace_enabled);
 }
 #else	/* !CONFIG_KPROBES_ON_FTRACE */
-static inline int prepare_kprobe(struct kprobe *p)
-{
-	return arch_prepare_kprobe(p);
-}
-
 static inline int arm_kprobe_ftrace(struct kprobe *p)
 {
 	return -ENODEV;
@@ -1129,7 +1130,15 @@ static inline int disarm_kprobe_ftrace(struct kprobe *p)
 }
 #endif
 
-/* Arm a kprobe with text_mutex */
+static int prepare_kprobe(struct kprobe *p)
+{
+	/* Must ensure p->addr is really on ftrace */
+	if (kprobe_ftrace(p))
+		return arch_prepare_kprobe_ftrace(p);
+
+	return arch_prepare_kprobe(p);
+}
+
 static int arm_kprobe(struct kprobe *kp)
 {
 	if (unlikely(kprobe_ftrace(kp)))
@@ -1144,7 +1153,6 @@ static int arm_kprobe(struct kprobe *kp)
 	return 0;
 }
 
-/* Disarm a kprobe with text_mutex */
 static int disarm_kprobe(struct kprobe *kp, bool reopt)
 {
 	if (unlikely(kprobe_ftrace(kp)))
@@ -1194,17 +1202,17 @@ static void aggr_post_handler(struct kprobe *p, struct pt_regs *regs,
 }
 NOKPROBE_SYMBOL(aggr_post_handler);
 
-/* Walks the list and increments nmissed count for multiprobe case */
+/* Walks the list and increments 'nmissed' if 'p' has child probes. */
 void kprobes_inc_nmissed_count(struct kprobe *p)
 {
 	struct kprobe *kp;
+
 	if (!kprobe_aggrprobe(p)) {
 		p->nmissed++;
 	} else {
 		list_for_each_entry_rcu(kp, &p->list, list)
 			kp->nmissed++;
 	}
-	return;
 }
 NOKPROBE_SYMBOL(kprobes_inc_nmissed_count);
 
@@ -1222,9 +1230,9 @@ static void recycle_rp_inst(struct kretprobe_instance *ri)
 {
 	struct kretprobe *rp = get_kretprobe(ri);
 
-	if (likely(rp)) {
+	if (likely(rp))
 		freelist_add(&ri->freelist, &rp->freelist);
-	} else
+	else
 		call_rcu(&ri->rcu, free_rp_inst_rcu);
 }
 NOKPROBE_SYMBOL(recycle_rp_inst);
@@ -1251,9 +1259,9 @@ void kprobe_busy_end(void)
 
 /*
  * This function is called from delayed_put_task_struct() when a task is
- * dead and cleaned up to recycle any function-return probe instances
- * associated with this task. These left over instances represent probed
- * functions that have been called but will never return.
+ * dead and cleaned up to recycle any kretprobe instances associated with
+ * this task. These left over instances represent probed functions that
+ * have been called but will never return.
  */
 void kprobe_flush_task(struct task_struct *tk)
 {
@@ -1299,7 +1307,7 @@ static inline void free_rp_inst(struct kretprobe *rp)
 	}
 }
 
-/* Add the new probe to ap->list */
+/* Add the new probe to 'ap->list'. */
 static int add_new_kprobe(struct kprobe *ap, struct kprobe *p)
 {
 	if (p->post_handler)
@@ -1313,12 +1321,12 @@ static int add_new_kprobe(struct kprobe *ap, struct kprobe *p)
 }
 
 /*
- * Fill in the required fields of the "manager kprobe". Replace the
- * earlier kprobe in the hlist with the manager kprobe
+ * Fill in the required fields of the aggregator kprobe. Replace the
+ * earlier kprobe in the hlist with the aggregator kprobe.
  */
 static void init_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
 {
-	/* Copy p's insn slot to ap */
+	/* Copy the insn slot of 'p' to 'ap'. */
 	copy_kprobe(p, ap);
 	flush_insn_slot(ap);
 	ap->addr = p->addr;
@@ -1336,8 +1344,7 @@ static void init_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
 }
 
 /*
- * This is the second or subsequent kprobe at the address - handle
- * the intricacies
+ * This registers the second or subsequent kprobe at the same address.
  */
 static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
 {
@@ -1351,7 +1358,7 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
 	mutex_lock(&text_mutex);
 
 	if (!kprobe_aggrprobe(orig_p)) {
-		/* If orig_p is not an aggr_kprobe, create new aggr_kprobe. */
+		/* If 'orig_p' is not an 'aggr_kprobe', create new one. */
 		ap = alloc_aggr_kprobe(orig_p);
 		if (!ap) {
 			ret = -ENOMEM;
@@ -1376,8 +1383,8 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
 		if (ret)
 			/*
 			 * Even if fail to allocate new slot, don't need to
-			 * free aggr_probe. It will be used next time, or
-			 * freed by unregister_kprobe.
+			 * free the 'ap'. It will be used next time, or
+			 * freed by unregister_kprobe().
 			 */
 			goto out;
 
@@ -1392,7 +1399,7 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
 			    | KPROBE_FLAG_DISABLED;
 	}
 
-	/* Copy ap's insn slot to p */
+	/* Copy the insn slot of 'p' to 'ap'. */
 	copy_kprobe(ap, p);
 	ret = add_new_kprobe(ap, p);
 
@@ -1418,7 +1425,7 @@ out:
 
 bool __weak arch_within_kprobe_blacklist(unsigned long addr)
 {
-	/* The __kprobes marked functions and entry code must not be probed */
+	/* The '__kprobes' functions and entry code must not be probed. */
 	return addr >= (unsigned long)__kprobes_text_start &&
 	       addr < (unsigned long)__kprobes_text_end;
 }
@@ -1430,8 +1437,8 @@ static bool __within_kprobe_blacklist(unsigned long addr)
 	if (arch_within_kprobe_blacklist(addr))
 		return true;
 	/*
-	 * If there exists a kprobe_blacklist, verify and
-	 * fail any probe registration in the prohibited area
+	 * If 'kprobe_blacklist' is defined, check the address and
+	 * reject any probe registration in the prohibited area.
 	 */
 	list_for_each_entry(ent, &kprobe_blacklist, list) {
 		if (addr >= ent->start_addr && addr < ent->end_addr)
@@ -1461,7 +1468,7 @@ bool within_kprobe_blacklist(unsigned long addr)
 }
 
 /*
- * If we have a symbol_name argument, look it up and add the offset field
+ * If 'symbol_name' is specified, look it up and add the 'offset'
  * to it. This way, we can specify a relative address to a symbol.
  * This returns encoded errors if it fails to look up symbol or invalid
  * combination of parameters.
@@ -1491,7 +1498,10 @@ static kprobe_opcode_t *kprobe_addr(struct kprobe *p)
 	return _kprobe_addr(p->addr, p->symbol_name, p->offset);
 }
 
-/* Check passed kprobe is valid and return kprobe in kprobe_table. */
+/*
+ * Check the 'p' is valid and return the aggregator kprobe
+ * at the same address.
+ */
 static struct kprobe *__get_valid_kprobe(struct kprobe *p)
 {
 	struct kprobe *ap, *list_p;
@@ -1529,7 +1539,7 @@ static inline int warn_kprobe_rereg(struct kprobe *p)
 	return ret;
 }
 
-int __weak arch_check_ftrace_location(struct kprobe *p)
+static int check_ftrace_location(struct kprobe *p)
 {
 	unsigned long ftrace_addr;
 
@@ -1552,7 +1562,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
 {
 	int ret;
 
-	ret = arch_check_ftrace_location(p);
+	ret = check_ftrace_location(p);
 	if (ret)
 		return ret;
 	jump_label_lock();
@@ -1568,7 +1578,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
 		goto out;
 	}
 
-	/* Check if are we probing a module */
+	/* Check if 'p' is probing a module. */
 	*probed_mod = __module_text_address((unsigned long) p->addr);
 	if (*probed_mod) {
 		/*
@@ -1581,7 +1591,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
 		}
 
 		/*
-		 * If the module freed .init.text, we couldn't insert
+		 * If the module freed '.init.text', we couldn't insert
 		 * kprobes in there.
 		 */
 		if (within_module_init((unsigned long)p->addr, *probed_mod) &&
@@ -1628,7 +1638,7 @@ int register_kprobe(struct kprobe *p)
 
 	old_p = get_kprobe(p->addr);
 	if (old_p) {
-		/* Since this may unoptimize old_p, locking text_mutex. */
+		/* Since this may unoptimize 'old_p', locking 'text_mutex'. */
 		ret = register_aggr_kprobe(old_p, p);
 		goto out;
 	}
@@ -1667,8 +1677,8 @@ out:
 }
 EXPORT_SYMBOL_GPL(register_kprobe);
 
-/* Check if all probes on the aggrprobe are disabled */
-static int aggr_kprobe_disabled(struct kprobe *ap)
+/* Check if all probes on the 'ap' are disabled. */
+static bool aggr_kprobe_disabled(struct kprobe *ap)
 {
 	struct kprobe *kp;
 
@@ -1677,20 +1687,21 @@ static int aggr_kprobe_disabled(struct kprobe *ap)
 	list_for_each_entry(kp, &ap->list, list)
 		if (!kprobe_disabled(kp))
 			/*
-			 * There is an active probe on the list.
-			 * We can't disable this ap.
+			 * Since there is an active probe on the list,
+			 * we can't disable this 'ap'.
 			 */
-			return 0;
+			return false;
 
-	return 1;
+	return true;
 }
 
-/* Disable one kprobe: Make sure called under kprobe_mutex is locked */
 static struct kprobe *__disable_kprobe(struct kprobe *p)
 {
 	struct kprobe *orig_p;
 	int ret;
 
+	lockdep_assert_held(&kprobe_mutex);
+
 	/* Get an original kprobe for return */
 	orig_p = __get_valid_kprobe(p);
 	if (unlikely(orig_p == NULL))
@@ -1704,7 +1715,7 @@ static struct kprobe *__disable_kprobe(struct kprobe *p)
 		/* Try to disarm and disable this/parent probe */
 		if (p == orig_p || aggr_kprobe_disabled(orig_p)) {
 			/*
-			 * If kprobes_all_disarmed is set, orig_p
+			 * If 'kprobes_all_disarmed' is set, 'orig_p'
 			 * should have already been disarmed, so
 			 * skip unneed disarming process.
 			 */
@@ -1850,53 +1861,105 @@ static struct notifier_block kprobe_exceptions_nb = {
 	.priority = 0x7fffffff /* we need to be notified first */
 };
 
-unsigned long __weak arch_deref_entry_point(void *entry)
+#ifdef CONFIG_KRETPROBES
+
+/* This assumes the 'tsk' is the current task or the is not running. */
+static kprobe_opcode_t *__kretprobe_find_ret_addr(struct task_struct *tsk,
+						  struct llist_node **cur)
 {
-	return (unsigned long)entry;
+	struct kretprobe_instance *ri = NULL;
+	struct llist_node *node = *cur;
+
+	if (!node)
+		node = tsk->kretprobe_instances.first;
+	else
+		node = node->next;
+
+	while (node) {
+		ri = container_of(node, struct kretprobe_instance, llist);
+		if (ri->ret_addr != kretprobe_trampoline_addr()) {
+			*cur = node;
+			return ri->ret_addr;
+		}
+		node = node->next;
+	}
+	return NULL;
 }
+NOKPROBE_SYMBOL(__kretprobe_find_ret_addr);
 
-#ifdef CONFIG_KRETPROBES
+/**
+ * kretprobe_find_ret_addr -- Find correct return address modified by kretprobe
+ * @tsk: Target task
+ * @fp: A frame pointer
+ * @cur: a storage of the loop cursor llist_node pointer for next call
+ *
+ * Find the correct return address modified by a kretprobe on @tsk in unsigned
+ * long type. If it finds the return address, this returns that address value,
+ * or this returns 0.
+ * The @tsk must be 'current' or a task which is not running. @fp is a hint
+ * to get the currect return address - which is compared with the
+ * kretprobe_instance::fp field. The @cur is a loop cursor for searching the
+ * kretprobe return addresses on the @tsk. The '*@cur' should be NULL at the
+ * first call, but '@cur' itself must NOT NULL.
+ */
+unsigned long kretprobe_find_ret_addr(struct task_struct *tsk, void *fp,
+				      struct llist_node **cur)
+{
+	struct kretprobe_instance *ri = NULL;
+	kprobe_opcode_t *ret;
+
+	if (WARN_ON_ONCE(!cur))
+		return 0;
+
+	do {
+		ret = __kretprobe_find_ret_addr(tsk, cur);
+		if (!ret)
+			break;
+		ri = container_of(*cur, struct kretprobe_instance, llist);
+	} while (ri->fp != fp);
+
+	return (unsigned long)ret;
+}
+NOKPROBE_SYMBOL(kretprobe_find_ret_addr);
+
+void __weak arch_kretprobe_fixup_return(struct pt_regs *regs,
+					kprobe_opcode_t *correct_ret_addr)
+{
+	/*
+	 * Do nothing by default. Please fill this to update the fake return
+	 * address on the stack with the correct one on each arch if possible.
+	 */
+}
 
 unsigned long __kretprobe_trampoline_handler(struct pt_regs *regs,
-					     void *trampoline_address,
 					     void *frame_pointer)
 {
 	kprobe_opcode_t *correct_ret_addr = NULL;
 	struct kretprobe_instance *ri = NULL;
-	struct llist_node *first, *node;
+	struct llist_node *first, *node = NULL;
 	struct kretprobe *rp;
 
-	/* Find all nodes for this frame. */
-	first = node = current->kretprobe_instances.first;
-	while (node) {
-		ri = container_of(node, struct kretprobe_instance, llist);
-
-		BUG_ON(ri->fp != frame_pointer);
-
-		if (ri->ret_addr != trampoline_address) {
-			correct_ret_addr = ri->ret_addr;
-			/*
-			 * This is the real return address. Any other
-			 * instances associated with this task are for
-			 * other calls deeper on the call stack
-			 */
-			goto found;
-		}
-
-		node = node->next;
+	/* Find correct address and all nodes for this frame. */
+	correct_ret_addr = __kretprobe_find_ret_addr(current, &node);
+	if (!correct_ret_addr) {
+		pr_err("kretprobe: Return address not found, not execute handler. Maybe there is a bug in the kernel.\n");
+		BUG_ON(1);
 	}
-	pr_err("Oops! Kretprobe fails to find correct return address.\n");
-	BUG_ON(1);
 
-found:
-	/* Unlink all nodes for this frame. */
-	current->kretprobe_instances.first = node->next;
-	node->next = NULL;
+	/*
+	 * Set the return address as the instruction pointer, because if the
+	 * user handler calls stack_trace_save_regs() with this 'regs',
+	 * the stack trace will start from the instruction pointer.
+	 */
+	instruction_pointer_set(regs, (unsigned long)correct_ret_addr);
 
-	/* Run them..  */
+	/* Run the user handler of the nodes. */
+	first = current->kretprobe_instances.first;
 	while (first) {
 		ri = container_of(first, struct kretprobe_instance, llist);
-		first = first->next;
+
+		if (WARN_ON_ONCE(ri->fp != frame_pointer))
+			break;
 
 		rp = get_kretprobe(ri);
 		if (rp && rp->handler) {
@@ -1907,6 +1970,23 @@ found:
 			rp->handler(ri, regs);
 			__this_cpu_write(current_kprobe, prev);
 		}
+		if (first == node)
+			break;
+
+		first = first->next;
+	}
+
+	arch_kretprobe_fixup_return(regs, correct_ret_addr);
+
+	/* Unlink all nodes for this frame. */
+	first = current->kretprobe_instances.first;
+	current->kretprobe_instances.first = node->next;
+	node->next = NULL;
+
+	/* Recycle free instances. */
+	while (first) {
+		ri = container_of(first, struct kretprobe_instance, llist);
+		first = first->next;
 
 		recycle_rp_inst(ri);
 	}
@@ -1991,7 +2071,7 @@ int register_kretprobe(struct kretprobe *rp)
 	if (ret)
 		return ret;
 
-	/* If only rp->kp.addr is specified, check reregistering kprobes */
+	/* If only 'rp->kp.addr' is specified, check reregistering kprobes */
 	if (rp->kp.addr && warn_kprobe_rereg(&rp->kp))
 		return -EINVAL;
 
@@ -2096,13 +2176,13 @@ EXPORT_SYMBOL_GPL(unregister_kretprobes);
 #else /* CONFIG_KRETPROBES */
 int register_kretprobe(struct kretprobe *rp)
 {
-	return -ENOSYS;
+	return -EOPNOTSUPP;
 }
 EXPORT_SYMBOL_GPL(register_kretprobe);
 
 int register_kretprobes(struct kretprobe **rps, int num)
 {
-	return -ENOSYS;
+	return -EOPNOTSUPP;
 }
 EXPORT_SYMBOL_GPL(register_kretprobes);
 
@@ -2151,7 +2231,7 @@ static void kill_kprobe(struct kprobe *p)
 	/*
 	 * The module is going away. We should disarm the kprobe which
 	 * is using ftrace, because ftrace framework is still available at
-	 * MODULE_STATE_GOING notification.
+	 * 'MODULE_STATE_GOING' notification.
 	 */
 	if (kprobe_ftrace(p) && !kprobe_disabled(p) && !kprobes_all_disarmed)
 		disarm_kprobe_ftrace(p);
@@ -2214,8 +2294,7 @@ EXPORT_SYMBOL_GPL(enable_kprobe);
 /* Caller must NOT call this in usual path. This is only for critical case */
 void dump_kprobe(struct kprobe *kp)
 {
-	pr_err("Dumping kprobe:\n");
-	pr_err("Name: %s\nOffset: %x\nAddress: %pS\n",
+	pr_err("Dump kprobe:\n.symbol_name = %s, .offset = %x, .addr = %pS\n",
 	       kp->symbol_name, kp->offset, kp->addr);
 }
 NOKPROBE_SYMBOL(dump_kprobe);
@@ -2317,7 +2396,7 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
 	int ret;
 
 	for (iter = start; iter < end; iter++) {
-		entry = arch_deref_entry_point((void *)*iter);
+		entry = (unsigned long)dereference_symbol_descriptor((void *)*iter);
 		ret = kprobe_add_ksym_blacklist(entry);
 		if (ret == -EINVAL)
 			continue;
@@ -2325,13 +2404,13 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
 			return ret;
 	}
 
-	/* Symbols in __kprobes_text are blacklisted */
+	/* Symbols in '__kprobes_text' are blacklisted */
 	ret = kprobe_add_area_blacklist((unsigned long)__kprobes_text_start,
 					(unsigned long)__kprobes_text_end);
 	if (ret)
 		return ret;
 
-	/* Symbols in noinstr section are blacklisted */
+	/* Symbols in 'noinstr' section are blacklisted */
 	ret = kprobe_add_area_blacklist((unsigned long)__noinstr_text_start,
 					(unsigned long)__noinstr_text_end);
 
@@ -2403,9 +2482,9 @@ static int kprobes_module_callback(struct notifier_block *nb,
 		return NOTIFY_DONE;
 
 	/*
-	 * When MODULE_STATE_GOING was notified, both of module .text and
-	 * .init.text sections would be freed. When MODULE_STATE_LIVE was
-	 * notified, only .init.text section would be freed. We need to
+	 * When 'MODULE_STATE_GOING' was notified, both of module '.text' and
+	 * '.init.text' sections would be freed. When 'MODULE_STATE_LIVE' was
+	 * notified, only '.init.text' section would be freed. We need to
 	 * disable kprobes which have been inserted in the sections.
 	 */
 	mutex_lock(&kprobe_mutex);
@@ -2422,9 +2501,9 @@ static int kprobes_module_callback(struct notifier_block *nb,
 				 *
 				 * Note, this will also move any optimized probes
 				 * that are pending to be removed from their
-				 * corresponding lists to the freeing_list and
+				 * corresponding lists to the 'freeing_list' and
 				 * will not be touched by the delayed
-				 * kprobe_optimizer work handler.
+				 * kprobe_optimizer() work handler.
 				 */
 				kill_kprobe(p);
 			}
@@ -2440,10 +2519,6 @@ static struct notifier_block kprobe_module_nb = {
 	.priority = 0
 };
 
-/* Markers of _kprobe_blacklist section */
-extern unsigned long __start_kprobe_blacklist[];
-extern unsigned long __stop_kprobe_blacklist[];
-
 void kprobe_free_init_mem(void)
 {
 	void *start = (void *)(&__init_begin);
@@ -2454,7 +2529,7 @@ void kprobe_free_init_mem(void)
 
 	mutex_lock(&kprobe_mutex);
 
-	/* Kill all kprobes on initmem */
+	/* Kill all kprobes on initmem because the target code has been freed. */
 	for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
 		head = &kprobe_table[i];
 		hlist_for_each_entry(p, head, hlist) {
@@ -2477,10 +2552,8 @@ static int __init init_kprobes(void)
 
 	err = populate_kprobe_blacklist(__start_kprobe_blacklist,
 					__stop_kprobe_blacklist);
-	if (err) {
-		pr_err("kprobes: failed to populate blacklist: %d\n", err);
-		pr_err("Please take care of using kprobes.\n");
-	}
+	if (err)
+		pr_err("Failed to populate blacklist (error %d), kprobes not restricted, be careful using them!\n", err);
 
 	if (kretprobe_blacklist_size) {
 		/* lookup the function address from its name */
@@ -2488,7 +2561,7 @@ static int __init init_kprobes(void)
 			kretprobe_blacklist[i].addr =
 				kprobe_lookup_name(kretprobe_blacklist[i].name, 0);
 			if (!kretprobe_blacklist[i].addr)
-				printk("kretprobe: lookup failed: %s\n",
+				pr_err("Failed to lookup symbol '%s' for kretprobe blacklist. Maybe the target function is removed or renamed.\n",
 				       kretprobe_blacklist[i].name);
 		}
 	}
@@ -2497,7 +2570,7 @@ static int __init init_kprobes(void)
 	kprobes_all_disarmed = false;
 
 #if defined(CONFIG_OPTPROBES) && defined(__ARCH_WANT_KPROBES_INSN_SLOT)
-	/* Init kprobe_optinsn_slots for allocation */
+	/* Init 'kprobe_optinsn_slots' for allocation */
 	kprobe_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
 #endif
 
@@ -2508,9 +2581,6 @@ static int __init init_kprobes(void)
 		err = register_module_notifier(&kprobe_module_nb);
 
 	kprobes_initialized = (err == 0);
-
-	if (!err)
-		init_test_probes();
 	return err;
 }
 early_initcall(init_kprobes);
@@ -2631,7 +2701,7 @@ static int kprobe_blacklist_seq_show(struct seq_file *m, void *v)
 		list_entry(v, struct kprobe_blacklist_entry, list);
 
 	/*
-	 * If /proc/kallsyms is not showing kernel address, we won't
+	 * If '/proc/kallsyms' is not showing kernel address, we won't
 	 * show them here either.
 	 */
 	if (!kallsyms_show_value(m->file->f_cred))
@@ -2692,7 +2762,7 @@ static int arm_all_kprobes(void)
 	}
 
 	if (errors)
-		pr_warn("Kprobes globally enabled, but failed to arm %d out of %d probes\n",
+		pr_warn("Kprobes globally enabled, but failed to enable %d out of %d probes. Please check which kprobes are kept disabled via debugfs.\n",
 			errors, total);
 	else
 		pr_info("Kprobes globally enabled\n");
@@ -2735,7 +2805,7 @@ static int disarm_all_kprobes(void)
 	}
 
 	if (errors)
-		pr_warn("Kprobes globally disabled, but failed to disarm %d out of %d probes\n",
+		pr_warn("Kprobes globally disabled, but failed to disable %d out of %d probes. Please check which kprobes are kept enabled via debugfs.\n",
 			errors, total);
 	else
 		pr_info("Kprobes globally disabled\n");
@@ -2770,30 +2840,14 @@ static ssize_t read_enabled_file_bool(struct file *file,
 static ssize_t write_enabled_file_bool(struct file *file,
 	       const char __user *user_buf, size_t count, loff_t *ppos)
 {
-	char buf[32];
-	size_t buf_size;
-	int ret = 0;
-
-	buf_size = min(count, (sizeof(buf)-1));
-	if (copy_from_user(buf, user_buf, buf_size))
-		return -EFAULT;
+	bool enable;
+	int ret;
 
-	buf[buf_size] = '\0';
-	switch (buf[0]) {
-	case 'y':
-	case 'Y':
-	case '1':
-		ret = arm_all_kprobes();
-		break;
-	case 'n':
-	case 'N':
-	case '0':
-		ret = disarm_all_kprobes();
-		break;
-	default:
-		return -EINVAL;
-	}
+	ret = kstrtobool_from_user(user_buf, count, &enable);
+	if (ret)
+		return ret;
 
+	ret = enable ? arm_all_kprobes() : disarm_all_kprobes();
 	if (ret)
 		return ret;
 
@@ -2809,13 +2863,12 @@ static const struct file_operations fops_kp = {
 static int __init debugfs_kprobe_init(void)
 {
 	struct dentry *dir;
-	unsigned int value = 1;
 
 	dir = debugfs_create_dir("kprobes", NULL);
 
 	debugfs_create_file("list", 0400, dir, NULL, &kprobes_fops);
 
-	debugfs_create_file("enabled", 0600, dir, &value, &fops_kp);
+	debugfs_create_file("enabled", 0600, dir, NULL, &fops_kp);
 
 	debugfs_create_file("blacklist", 0400, dir, NULL,
 			    &kprobe_blacklist_fops);