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 */
+