Merge branch 'tracing/hw-breakpoints' into perf/core

Conflicts:
	arch/x86/kernel/kprobes.c
	kernel/trace/Makefile

Merge reason: hw-breakpoints perf integration is looking
              good in testing and in reviews, plus conflicts
              are mounting up - so merge & resolve.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

6 files changed, 654 insertions, 0 deletions

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index f05671609a89..d006554888dc 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -339,6 +339,27 @@ config POWER_TRACER
 	  power management decisions, specifically the C-state and P-state
 	  behavior.
 
+config KSYM_TRACER
+	bool "Trace read and write access on kernel memory locations"
+	depends on HAVE_HW_BREAKPOINT
+	select TRACING
+	help
+	  This tracer helps find read and write operations on any given kernel
+	  symbol i.e. /proc/kallsyms.
+
+config PROFILE_KSYM_TRACER
+	bool "Profile all kernel memory accesses on 'watched' variables"
+	depends on KSYM_TRACER
+	help
+	  This tracer profiles kernel accesses on variables watched through the
+	  ksym tracer ftrace plugin. Depending upon the hardware, all read
+	  and write operations on kernel variables can be monitored for
+	  accesses.
+
+	  The results will be displayed in:
+	  /debugfs/tracing/profile_ksym
+
+	  Say N if unsure.
 
 config STACK_TRACER
 	bool "Trace max stack"
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index edc3a3cca1a1..cd9ecd89ec77 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -54,6 +54,7 @@ obj-$(CONFIG_FTRACE_SYSCALLS) += trace_syscalls.o
 obj-$(CONFIG_EVENT_PROFILE) += trace_event_profile.o
 obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o
 obj-$(CONFIG_KPROBE_EVENT) += trace_kprobe.o
+obj-$(CONFIG_KSYM_TRACER) += trace_ksym.o
 obj-$(CONFIG_EVENT_TRACING) += power-traces.o
 
 libftrace-y := ftrace.o
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index b4e4212e66d7..4da6ede74401 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -11,6 +11,7 @@
 #include <linux/ftrace.h>
 #include <trace/boot.h>
 #include <linux/kmemtrace.h>
+#include <linux/hw_breakpoint.h>
 
 #include <linux/trace_seq.h>
 #include <linux/ftrace_event.h>
@@ -37,6 +38,7 @@ enum trace_type {
 	TRACE_KMEM_ALLOC,
 	TRACE_KMEM_FREE,
 	TRACE_BLK,
+	TRACE_KSYM,
 
 	__TRACE_LAST_TYPE,
 };
@@ -232,6 +234,7 @@ extern void __ftrace_bad_type(void);
 			  TRACE_KMEM_ALLOC);	\
 		IF_ASSIGN(var, ent, struct kmemtrace_free_entry,	\
 			  TRACE_KMEM_FREE);	\
+		IF_ASSIGN(var, ent, struct ksym_trace_entry, TRACE_KSYM);\
 		__ftrace_bad_type();					\
 	} while (0)
 
@@ -387,6 +390,8 @@ int register_tracer(struct tracer *type);
 void unregister_tracer(struct tracer *type);
 int is_tracing_stopped(void);
 
+extern int process_new_ksym_entry(char *ksymname, int op, unsigned long addr);
+
 extern unsigned long nsecs_to_usecs(unsigned long nsecs);
 
 #ifdef CONFIG_TRACER_MAX_TRACE
@@ -461,6 +466,8 @@ extern int trace_selftest_startup_branch(struct tracer *trace,
 					 struct trace_array *tr);
 extern int trace_selftest_startup_hw_branches(struct tracer *trace,
 					      struct trace_array *tr);
+extern int trace_selftest_startup_ksym(struct tracer *trace,
+					 struct trace_array *tr);
 #endif /* CONFIG_FTRACE_STARTUP_TEST */
 
 extern void *head_page(struct trace_array_cpu *data);
diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
index ead3d724599d..c16a08f399df 100644
--- a/kernel/trace/trace_entries.h
+++ b/kernel/trace/trace_entries.h
@@ -364,3 +364,19 @@ FTRACE_ENTRY(kmem_free, kmemtrace_free_entry,
 	F_printk("type:%u call_site:%lx ptr:%p",
 		 __entry->type_id, __entry->call_site, __entry->ptr)
 );
+
+FTRACE_ENTRY(ksym_trace, ksym_trace_entry,
+
+	TRACE_KSYM,
+
+	F_STRUCT(
+		__field(	unsigned long,	ip			  )
+		__field(	unsigned char,	type			  )
+		__array(	char	     ,	cmd,	   TASK_COMM_LEN  )
+		__field(	unsigned long,  addr			  )
+	),
+
+	F_printk("ip: %pF type: %d ksym_name: %pS cmd: %s",
+		(void *)__entry->ip, (unsigned int)__entry->type,
+		(void *)__entry->addr,  __entry->cmd)
+);
diff --git a/kernel/trace/trace_ksym.c b/kernel/trace/trace_ksym.c
new file mode 100644
index 000000000000..11935b53a6cb
--- /dev/null
+++ b/kernel/trace/trace_ksym.c
@@ -0,0 +1,554 @@
+/*
+ * trace_ksym.c - Kernel Symbol Tracer
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2009
+ */
+
+#include <linux/kallsyms.h>
+#include <linux/uaccess.h>
+#include <linux/debugfs.h>
+#include <linux/ftrace.h>
+#include <linux/module.h>
+#include <linux/fs.h>
+
+#include "trace_output.h"
+#include "trace_stat.h"
+#include "trace.h"
+
+#include <linux/hw_breakpoint.h>
+#include <asm/hw_breakpoint.h>
+
+/*
+ * For now, let us restrict the no. of symbols traced simultaneously to number
+ * of available hardware breakpoint registers.
+ */
+#define KSYM_TRACER_MAX HBP_NUM
+
+#define KSYM_TRACER_OP_LEN 3 /* rw- */
+
+struct trace_ksym {
+	struct perf_event	**ksym_hbp;
+	unsigned long		ksym_addr;
+	int			type;
+	int			len;
+#ifdef CONFIG_PROFILE_KSYM_TRACER
+	unsigned long		counter;
+#endif
+	struct hlist_node	ksym_hlist;
+};
+
+static struct trace_array *ksym_trace_array;
+
+static unsigned int ksym_filter_entry_count;
+static unsigned int ksym_tracing_enabled;
+
+static HLIST_HEAD(ksym_filter_head);
+
+static DEFINE_MUTEX(ksym_tracer_mutex);
+
+#ifdef CONFIG_PROFILE_KSYM_TRACER
+
+#define MAX_UL_INT 0xffffffff
+
+void ksym_collect_stats(unsigned long hbp_hit_addr)
+{
+	struct hlist_node *node;
+	struct trace_ksym *entry;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(entry, node, &ksym_filter_head, ksym_hlist) {
+		if ((entry->ksym_addr == hbp_hit_addr) &&
+		    (entry->counter <= MAX_UL_INT)) {
+			entry->counter++;
+			break;
+		}
+	}
+	rcu_read_unlock();
+}
+#endif /* CONFIG_PROFILE_KSYM_TRACER */
+
+void ksym_hbp_handler(struct perf_event *hbp, void *data)
+{
+	struct ring_buffer_event *event;
+	struct ksym_trace_entry *entry;
+	struct pt_regs *regs = data;
+	struct ring_buffer *buffer;
+	int pc;
+
+	if (!ksym_tracing_enabled)
+		return;
+
+	buffer = ksym_trace_array->buffer;
+
+	pc = preempt_count();
+
+	event = trace_buffer_lock_reserve(buffer, TRACE_KSYM,
+							sizeof(*entry), 0, pc);
+	if (!event)
+		return;
+
+	entry		= ring_buffer_event_data(event);
+	entry->ip	= instruction_pointer(regs);
+	entry->type	= hw_breakpoint_type(hbp);
+	entry->addr	= hw_breakpoint_addr(hbp);
+	strlcpy(entry->cmd, current->comm, TASK_COMM_LEN);
+
+#ifdef CONFIG_PROFILE_KSYM_TRACER
+	ksym_collect_stats(hw_breakpoint_addr(hbp));
+#endif /* CONFIG_PROFILE_KSYM_TRACER */
+
+	trace_buffer_unlock_commit(buffer, event, 0, pc);
+}
+
+/* Valid access types are represented as
+ *
+ * rw- : Set Read/Write Access Breakpoint
+ * -w- : Set Write Access Breakpoint
+ * --- : Clear Breakpoints
+ * --x : Set Execution Break points (Not available yet)
+ *
+ */
+static int ksym_trace_get_access_type(char *str)
+{
+	int access = 0;
+
+	if (str[0] == 'r')
+		access |= HW_BREAKPOINT_R;
+
+	if (str[1] == 'w')
+		access |= HW_BREAKPOINT_W;
+
+	if (str[2] == 'x')
+		access |= HW_BREAKPOINT_X;
+
+	switch (access) {
+	case HW_BREAKPOINT_R:
+	case HW_BREAKPOINT_W:
+	case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
+		return access;
+	default:
+		return -EINVAL;
+	}
+}
+
+/*
+ * There can be several possible malformed requests and we attempt to capture
+ * all of them. We enumerate some of the rules
+ * 1. We will not allow kernel symbols with ':' since it is used as a delimiter.
+ *    i.e. multiple ':' symbols disallowed. Possible uses are of the form
+ *    <module>:<ksym_name>:<op>.
+ * 2. No delimiter symbol ':' in the input string
+ * 3. Spurious operator symbols or symbols not in their respective positions
+ * 4. <ksym_name>:--- i.e. clear breakpoint request when ksym_name not in file
+ * 5. Kernel symbol not a part of /proc/kallsyms
+ * 6. Duplicate requests
+ */
+static int parse_ksym_trace_str(char *input_string, char **ksymname,
+							unsigned long *addr)
+{
+	int ret;
+
+	*ksymname = strsep(&input_string, ":");
+	*addr = kallsyms_lookup_name(*ksymname);
+
+	/* Check for malformed request: (2), (1) and (5) */
+	if ((!input_string) ||
+	    (strlen(input_string) != KSYM_TRACER_OP_LEN) ||
+	    (*addr == 0))
+		return -EINVAL;;
+
+	ret = ksym_trace_get_access_type(input_string);
+
+	return ret;
+}
+
+int process_new_ksym_entry(char *ksymname, int op, unsigned long addr)
+{
+	struct trace_ksym *entry;
+	int ret = -ENOMEM;
+
+	if (ksym_filter_entry_count >= KSYM_TRACER_MAX) {
+		printk(KERN_ERR "ksym_tracer: Maximum limit:(%d) reached. No"
+		" new requests for tracing can be accepted now.\n",
+			KSYM_TRACER_MAX);
+		return -ENOSPC;
+	}
+
+	entry = kzalloc(sizeof(struct trace_ksym), GFP_KERNEL);
+	if (!entry)
+		return -ENOMEM;
+
+	entry->type = op;
+	entry->ksym_addr = addr;
+	entry->len = HW_BREAKPOINT_LEN_4;
+
+	ret = -EAGAIN;
+	entry->ksym_hbp = register_wide_hw_breakpoint(entry->ksym_addr,
+					entry->len, entry->type,
+					ksym_hbp_handler, true);
+	if (IS_ERR(entry->ksym_hbp)) {
+		entry->ksym_hbp = NULL;
+		ret = PTR_ERR(entry->ksym_hbp);
+	}
+
+	if (!entry->ksym_hbp) {
+		printk(KERN_INFO "ksym_tracer request failed. Try again"
+					" later!!\n");
+		goto err;
+	}
+
+	hlist_add_head_rcu(&(entry->ksym_hlist), &ksym_filter_head);
+	ksym_filter_entry_count++;
+
+	return 0;
+
+err:
+	kfree(entry);
+
+	return ret;
+}
+
+static ssize_t ksym_trace_filter_read(struct file *filp, char __user *ubuf,
+						size_t count, loff_t *ppos)
+{
+	struct trace_ksym *entry;
+	struct hlist_node *node;
+	struct trace_seq *s;
+	ssize_t cnt = 0;
+	int ret;
+
+	s = kmalloc(sizeof(*s), GFP_KERNEL);
+	if (!s)
+		return -ENOMEM;
+	trace_seq_init(s);
+
+	mutex_lock(&ksym_tracer_mutex);
+
+	hlist_for_each_entry(entry, node, &ksym_filter_head, ksym_hlist) {
+		ret = trace_seq_printf(s, "%pS:", (void *)entry->ksym_addr);
+		if (entry->type == HW_BREAKPOINT_R)
+			ret = trace_seq_puts(s, "r--\n");
+		else if (entry->type == HW_BREAKPOINT_W)
+			ret = trace_seq_puts(s, "-w-\n");
+		else if (entry->type == (HW_BREAKPOINT_W | HW_BREAKPOINT_R))
+			ret = trace_seq_puts(s, "rw-\n");
+		WARN_ON_ONCE(!ret);
+	}
+
+	cnt = simple_read_from_buffer(ubuf, count, ppos, s->buffer, s->len);
+
+	mutex_unlock(&ksym_tracer_mutex);
+
+	kfree(s);
+
+	return cnt;
+}
+
+static void __ksym_trace_reset(void)
+{
+	struct trace_ksym *entry;
+	struct hlist_node *node, *node1;
+
+	mutex_lock(&ksym_tracer_mutex);
+	hlist_for_each_entry_safe(entry, node, node1, &ksym_filter_head,
+								ksym_hlist) {
+		unregister_wide_hw_breakpoint(entry->ksym_hbp);
+		ksym_filter_entry_count--;
+		hlist_del_rcu(&(entry->ksym_hlist));
+		synchronize_rcu();
+		kfree(entry);
+	}
+	mutex_unlock(&ksym_tracer_mutex);
+}
+
+static ssize_t ksym_trace_filter_write(struct file *file,
+					const char __user *buffer,
+						size_t count, loff_t *ppos)
+{
+	struct trace_ksym *entry;
+	struct hlist_node *node;
+	char *input_string, *ksymname = NULL;
+	unsigned long ksym_addr = 0;
+	int ret, op, changed = 0;
+
+	input_string = kzalloc(count + 1, GFP_KERNEL);
+	if (!input_string)
+		return -ENOMEM;
+
+	if (copy_from_user(input_string, buffer, count)) {
+		kfree(input_string);
+		return -EFAULT;
+	}
+	input_string[count] = '\0';
+
+	strstrip(input_string);
+
+	/*
+	 * Clear all breakpoints if:
+	 * 1: echo > ksym_trace_filter
+	 * 2: echo 0 > ksym_trace_filter
+	 * 3: echo "*:---" > ksym_trace_filter
+	 */
+	if (!input_string[0] || !strcmp(input_string, "0") ||
+	    !strcmp(input_string, "*:---")) {
+		__ksym_trace_reset();
+		kfree(input_string);
+		return count;
+	}
+
+	ret = op = parse_ksym_trace_str(input_string, &ksymname, &ksym_addr);
+	if (ret < 0) {
+		kfree(input_string);
+		return ret;
+	}
+
+	mutex_lock(&ksym_tracer_mutex);
+
+	ret = -EINVAL;
+	hlist_for_each_entry(entry, node, &ksym_filter_head, ksym_hlist) {
+		if (entry->ksym_addr == ksym_addr) {
+			/* Check for malformed request: (6) */
+			if (entry->type != op)
+				changed = 1;
+			else
+				goto out;
+			break;
+		}
+	}
+	if (changed) {
+		unregister_wide_hw_breakpoint(entry->ksym_hbp);
+		entry->type = op;
+		if (op > 0) {
+			entry->ksym_hbp =
+				register_wide_hw_breakpoint(entry->ksym_addr,
+					entry->len, entry->type,
+					ksym_hbp_handler, true);
+			if (IS_ERR(entry->ksym_hbp))
+				entry->ksym_hbp = NULL;
+			if (!entry->ksym_hbp)
+				goto out;
+		}
+		ksym_filter_entry_count--;
+		hlist_del_rcu(&(entry->ksym_hlist));
+		synchronize_rcu();
+		kfree(entry);
+		ret = 0;
+		goto out;
+	} else {
+		/* Check for malformed request: (4) */
+		if (op == 0)
+			goto out;
+		ret = process_new_ksym_entry(ksymname, op, ksym_addr);
+	}
+out:
+	mutex_unlock(&ksym_tracer_mutex);
+
+	kfree(input_string);
+
+	if (!ret)
+		ret = count;
+	return ret;
+}
+
+static const struct file_operations ksym_tracing_fops = {
+	.open		= tracing_open_generic,
+	.read		= ksym_trace_filter_read,
+	.write		= ksym_trace_filter_write,
+};
+
+static void ksym_trace_reset(struct trace_array *tr)
+{
+	ksym_tracing_enabled = 0;
+	__ksym_trace_reset();
+}
+
+static int ksym_trace_init(struct trace_array *tr)
+{
+	int cpu, ret = 0;
+
+	for_each_online_cpu(cpu)
+		tracing_reset(tr, cpu);
+	ksym_tracing_enabled = 1;
+	ksym_trace_array = tr;
+
+	return ret;
+}
+
+static void ksym_trace_print_header(struct seq_file *m)
+{
+	seq_puts(m,
+		 "#       TASK-PID   CPU#      Symbol                    "
+		 "Type    Function\n");
+	seq_puts(m,
+		 "#          |        |          |                       "
+		 " |         |\n");
+}
+
+static enum print_line_t ksym_trace_output(struct trace_iterator *iter)
+{
+	struct trace_entry *entry = iter->ent;
+	struct trace_seq *s = &iter->seq;
+	struct ksym_trace_entry *field;
+	char str[KSYM_SYMBOL_LEN];
+	int ret;
+
+	if (entry->type != TRACE_KSYM)
+		return TRACE_TYPE_UNHANDLED;
+
+	trace_assign_type(field, entry);
+
+	ret = trace_seq_printf(s, "%11s-%-5d [%03d] %pS", field->cmd,
+				entry->pid, iter->cpu, (char *)field->addr);
+	if (!ret)
+		return TRACE_TYPE_PARTIAL_LINE;
+
+	switch (field->type) {
+	case HW_BREAKPOINT_R:
+		ret = trace_seq_printf(s, " R  ");
+		break;
+	case HW_BREAKPOINT_W:
+		ret = trace_seq_printf(s, " W  ");
+		break;
+	case HW_BREAKPOINT_R | HW_BREAKPOINT_W:
+		ret = trace_seq_printf(s, " RW ");
+		break;
+	default:
+		return TRACE_TYPE_PARTIAL_LINE;
+	}
+
+	if (!ret)
+		return TRACE_TYPE_PARTIAL_LINE;
+
+	sprint_symbol(str, field->ip);
+	ret = trace_seq_printf(s, "%s\n", str);
+	if (!ret)
+		return TRACE_TYPE_PARTIAL_LINE;
+
+	return TRACE_TYPE_HANDLED;
+}
+
+struct tracer ksym_tracer __read_mostly =
+{
+	.name		= "ksym_tracer",
+	.init		= ksym_trace_init,
+	.reset		= ksym_trace_reset,
+#ifdef CONFIG_FTRACE_SELFTEST
+	.selftest	= trace_selftest_startup_ksym,
+#endif
+	.print_header   = ksym_trace_print_header,
+	.print_line	= ksym_trace_output
+};
+
+__init static int init_ksym_trace(void)
+{
+	struct dentry *d_tracer;
+	struct dentry *entry;
+
+	d_tracer = tracing_init_dentry();
+	ksym_filter_entry_count = 0;
+
+	entry = debugfs_create_file("ksym_trace_filter", 0644, d_tracer,
+				    NULL, &ksym_tracing_fops);
+	if (!entry)
+		pr_warning("Could not create debugfs "
+			   "'ksym_trace_filter' file\n");
+
+	return register_tracer(&ksym_tracer);
+}
+device_initcall(init_ksym_trace);
+
+
+#ifdef CONFIG_PROFILE_KSYM_TRACER
+static int ksym_tracer_stat_headers(struct seq_file *m)
+{
+	seq_puts(m, "  Access Type ");
+	seq_puts(m, "  Symbol                                       Counter\n");
+	seq_puts(m, "  ----------- ");
+	seq_puts(m, "  ------                                       -------\n");
+	return 0;
+}
+
+static int ksym_tracer_stat_show(struct seq_file *m, void *v)
+{
+	struct hlist_node *stat = v;
+	struct trace_ksym *entry;
+	int access_type = 0;
+	char fn_name[KSYM_NAME_LEN];
+
+	entry = hlist_entry(stat, struct trace_ksym, ksym_hlist);
+
+	access_type = entry->type;
+
+	switch (access_type) {
+	case HW_BREAKPOINT_R:
+		seq_puts(m, "  R           ");
+		break;
+	case HW_BREAKPOINT_W:
+		seq_puts(m, "  W           ");
+		break;
+	case HW_BREAKPOINT_R | HW_BREAKPOINT_W:
+		seq_puts(m, "  RW          ");
+		break;
+	default:
+		seq_puts(m, "  NA          ");
+	}
+
+	if (lookup_symbol_name(entry->ksym_addr, fn_name) >= 0)
+		seq_printf(m, "  %-36s", fn_name);
+	else
+		seq_printf(m, "  %-36s", "<NA>");
+	seq_printf(m, " %15lu\n", entry->counter);
+
+	return 0;
+}
+
+static void *ksym_tracer_stat_start(struct tracer_stat *trace)
+{
+	return ksym_filter_head.first;
+}
+
+static void *
+ksym_tracer_stat_next(void *v, int idx)
+{
+	struct hlist_node *stat = v;
+
+	return stat->next;
+}
+
+static struct tracer_stat ksym_tracer_stats = {
+	.name = "ksym_tracer",
+	.stat_start = ksym_tracer_stat_start,
+	.stat_next = ksym_tracer_stat_next,
+	.stat_headers = ksym_tracer_stat_headers,
+	.stat_show = ksym_tracer_stat_show
+};
+
+__init static int ksym_tracer_stat_init(void)
+{
+	int ret;
+
+	ret = register_stat_tracer(&ksym_tracer_stats);
+	if (ret) {
+		printk(KERN_WARNING "Warning: could not register "
+				    "ksym tracer stats\n");
+		return 1;
+	}
+
+	return 0;
+}
+fs_initcall(ksym_tracer_stat_init);
+#endif /* CONFIG_PROFILE_KSYM_TRACER */
diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index d2cdbabb4ead..dc98309e839a 100644
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -17,6 +17,7 @@ static inline int trace_valid_entry(struct trace_entry *entry)
 	case TRACE_GRAPH_ENT:
 	case TRACE_GRAPH_RET:
 	case TRACE_HW_BRANCHES:
+	case TRACE_KSYM:
 		return 1;
 	}
 	return 0;
@@ -808,3 +809,57 @@ trace_selftest_startup_hw_branches(struct tracer *trace,
 	return ret;
 }
 #endif /* CONFIG_HW_BRANCH_TRACER */
+
+#ifdef CONFIG_KSYM_TRACER
+static int ksym_selftest_dummy;
+
+int
+trace_selftest_startup_ksym(struct tracer *trace, struct trace_array *tr)
+{
+	unsigned long count;
+	int ret;
+
+	/* start the tracing */
+	ret = tracer_init(trace, tr);
+	if (ret) {
+		warn_failed_init_tracer(trace, ret);
+		return ret;
+	}
+
+	ksym_selftest_dummy = 0;
+	/* Register the read-write tracing request */
+
+	ret = process_new_ksym_entry("ksym_selftest_dummy",
+				     HW_BREAKPOINT_R | HW_BREAKPOINT_W,
+					(unsigned long)(&ksym_selftest_dummy));
+
+	if (ret < 0) {
+		printk(KERN_CONT "ksym_trace read-write startup test failed\n");
+		goto ret_path;
+	}
+	/* Perform a read and a write operation over the dummy variable to
+	 * trigger the tracer
+	 */
+	if (ksym_selftest_dummy == 0)
+		ksym_selftest_dummy++;
+
+	/* stop the tracing. */
+	tracing_stop();
+	/* check the trace buffer */
+	ret = trace_test_buffer(tr, &count);
+	trace->reset(tr);
+	tracing_start();
+
+	/* read & write operations - one each is performed on the dummy variable
+	 * triggering two entries in the trace buffer
+	 */
+	if (!ret && count != 2) {
+		printk(KERN_CONT "Ksym tracer startup test failed");
+		ret = -1;
+	}
+
+ret_path:
+	return ret;
+}
+#endif /* CONFIG_KSYM_TRACER */
+