Re: [Patch 11/12] ftrace plugin for kernel symbol tracing using HW Breakpoint interfaces - v4

Frederic Weisbecker
2009-05-11T22:14:44Z

On Mon, May 11, 2009 at 05:25:02PM +0530, K.Prasad wrote:
> This patch adds an ftrace plugin to detect and profile memory access over kernel
> variables. It uses HW Breakpoint interfaces to 'watch memory addresses.
>
> Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
> ---
> kernel/trace/Kconfig | 21 +
> kernel/trace/Makefile | 1
> kernel/trace/trace.h | 20 +
> kernel/trace/trace_ksym.c | 557 ++++++++++++++++++++++++++++++++++++++++++
> kernel/trace/trace_selftest.c | 37 ++
> 5 files changed, 636 insertions(+)
>
> Index: kernel/trace/Kconfig
> ===================================================================
> --- kernel/trace/Kconfig.orig
> +++ kernel/trace/Kconfig
> @@ -308,6 +308,27 @@ 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"
> Index: kernel/trace/Makefile
> ===================================================================
> --- kernel/trace/Makefile.orig
> +++ kernel/trace/Makefile
> @@ -50,5 +50,6 @@ obj-$(CONFIG_EVENT_TRACING) += trace_exp
> obj-$(CONFIG_FTRACE_SYSCALLS) += trace_syscalls.o
> obj-$(CONFIG_EVENT_PROFILE) += trace_event_profile.o
> obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o
> +obj-$(CONFIG_KSYM_TRACER) += trace_ksym.o
>
> libftrace-y := ftrace.o
> Index: kernel/trace/trace.h
> ===================================================================
> --- kernel/trace/trace.h.orig
> +++ kernel/trace/trace.h
> @@ -15,6 +15,10 @@
> #include <linux/trace_seq.h>
> #include <linux/ftrace_event.h>
>
> +#ifdef CONFIG_KSYM_TRACER
> +#include <asm/hw_breakpoint.h>
> +#endif
> +
> enum trace_type {
> __TRACE_FIRST_TYPE = 0,
>
> @@ -40,6 +44,7 @@ enum trace_type {
> TRACE_KMEM_FREE,
> TRACE_POWER,
> TRACE_BLK,
> + TRACE_KSYM,
>
> __TRACE_LAST_TYPE,
> };
> @@ -207,6 +212,18 @@ struct syscall_trace_exit {
> unsigned long ret;
> };
>
> +struct trace_ksym {
> + struct trace_entry ent;
> + struct hw_breakpoint *ksym_hbp;
> + unsigned long ksym_addr;
> + unsigned long ip;
> +#ifdef CONFIG_PROFILE_KSYM_TRACER
> + unsigned long counter;
> +#endif
> + struct hlist_node ksym_hlist;
> + char ksym_name[KSYM_NAME_LEN];
> + char p_name[TASK_COMM_LEN];
> +};
>
> /*
> * trace_flag_type is an enumeration that holds different
> @@ -323,6 +340,7 @@ extern void __ftrace_bad_type(void);
> TRACE_SYSCALL_ENTER); \
> IF_ASSIGN(var, ent, struct syscall_trace_exit, \
> TRACE_SYSCALL_EXIT); \
> + IF_ASSIGN(var, ent, struct trace_ksym, TRACE_KSYM); \
> __ftrace_bad_type(); \
> } while (0)
>
> @@ -538,6 +556,8 @@ extern int trace_selftest_startup_branch
> 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);
> Index: kernel/trace/trace_ksym.c
> ===================================================================
> --- /dev/null
> +++ kernel/trace/trace_ksym.c
> @@ -0,0 +1,557 @@
> +/*
> + * 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/jhash.h>
> +#include <linux/fs.h>
> +
> +#include "trace_output.h"
> +#include "trace_stat.h"
> +#include "trace.h"
> +
> +/* For now, let us restrict the no. of symbols traced simultaneously to number
> + * of available hardware breakpoint registers.
> + */
> +#define KSYM_TRACER_MAX HB_NUM
> +
> +#define KSYM_TRACER_OP_LEN 3 /* rw- */
> +#define KSYM_FILTER_ENTRY_LEN (KSYM_NAME_LEN + KSYM_TRACER_OP_LEN + 1)
> +
> +#ifdef CONFIG_FTRACE_SELFTEST
> +
> +static int ksym_selftest_dummy;
> +#define KSYM_SELFTEST_ENTRY "ksym_selftest_dummy"
> +
> +#endif /* CONFIG_FTRACE_SELFTEST */
> +
> +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);
> +
> +#ifdef CONFIG_PROFILE_KSYM_TRACER
> +
> +#define MAX_UL_INT 0xffffffff
> +
> +static DEFINE_MUTEX(ksym_tracer_mutex);
> +
> +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();

rcu looks a good idea to maintain your list.

> +}
> +#endif /* CONFIG_PROFILE_KSYM_TRACER */
> +
> +void ksym_hbp_handler(struct hw_breakpoint *hbp, struct pt_regs *regs)
> +{
> + struct ring_buffer_event *event;
> + struct trace_array *tr;
> + struct trace_ksym *entry;
> + int pc;
> +
> + if (!ksym_tracing_enabled)
> + return;
> +
> + tr = ksym_trace_array;
> + pc = preempt_count();
> +
> + event = trace_buffer_lock_reserve(tr, TRACE_KSYM,
> + sizeof(*entry), 0, pc);
> + if (!event)
> + return;
> +
> + entry = ring_buffer_event_data(event);
> + strlcpy(entry->ksym_name, hbp->info.name, KSYM_SYMBOL_LEN);
> + entry->ksym_hbp = hbp;
> + entry->ip = instruction_pointer(regs);
> + strlcpy(entry->p_name, current->comm, TASK_COMM_LEN);
> +#ifdef CONFIG_PROFILE_KSYM_TRACER
> + ksym_collect_stats(hbp->info.address);
> +#endif /* CONFIG_PROFILE_KSYM_TRACER */
> +
> + trace_buffer_unlock_commit(tr, 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 *access_str)
> +{
> + int pos, access = 0;
> +
> + for (pos = 0; pos < KSYM_TRACER_OP_LEN; pos++) {
> + switch (access_str[pos]) {
> + case 'r':
> + access += (pos == 0) ? 4 : -1;
> + break;
> + case 'w':
> + access += (pos == 1) ? 2 : -1;
> + break;
> + case '-':
> + break;
> + default:
> + return -EINVAL;
> + }
> + }
> +
> + switch (access) {
> + case 6:
> + access = HW_BREAKPOINT_RW;
> + break;
> + case 2:
> + access = HW_BREAKPOINT_WRITE;
> + break;
> + case 0:
> + access = 0;
> + }
> +
> + return access;
> +}
> +
> +/*
> + * 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)
> +{
> + char *delimiter = ":";
> + int ret;
> +
> + ret = -EINVAL;
> + *ksymname = strsep(&input_string, delimiter);
> + *addr = kallsyms_lookup_name(*ksymname);
> +
> + /* Check for malformed request: (2), (1) and (5) */
> + if ((!input_string) ||
> + (strlen(input_string) != (KSYM_TRACER_OP_LEN + 1)) ||
> + (*addr == 0))
> + goto return_code;
> + ret = ksym_trace_get_access_type(input_string);
> +
> +return_code:
> + return ret;
> +}
> +
> +static int process_new_ksym_entry(char *ksymname, int op, unsigned long addr)
> +{
> + struct trace_ksym *entry;
> + int ret;
> +
> + 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->ksym_hbp = kzalloc(sizeof(struct hw_breakpoint), GFP_KERNEL);
> + if (!entry->ksym_hbp) {
> + kfree(entry);
> + return -ENOMEM;
> + }
> +
> + entry->ksym_hbp->info.name = ksymname;
> + entry->ksym_hbp->info.type = op;
> + entry->ksym_addr = entry->ksym_hbp->info.address = addr;
> +#ifdef CONFIG_X86
> + entry->ksym_hbp->info.len = HW_BREAKPOINT_LEN_4;
> +#endif
> + entry->ksym_hbp->triggered = (void *)ksym_hbp_handler;
> +
> + ret = register_kernel_hw_breakpoint(entry->ksym_hbp);
> + if (ret < 0) {
> + printk(KERN_INFO "ksym_tracer request failed. Try again"
> + " later!!\n");
> + kfree(entry->ksym_hbp);
> + kfree(entry);
> + return -EAGAIN;
> + }
> + hlist_add_head_rcu(&(entry->ksym_hlist), &ksym_filter_head);

And then ksym_tracer_mutex protect concurrent writers.

> + ksym_filter_entry_count++;
> +
> + return 0;
> +}
> +
> +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;
> + char buf[KSYM_FILTER_ENTRY_LEN * KSYM_TRACER_MAX];
> + ssize_t ret, cnt = 0;
> +
> + mutex_lock(&ksym_tracer_mutex);
> +
> + hlist_for_each_entry(entry, node, &ksym_filter_head, ksym_hlist) {

And here you don't use the rcu version.
I guess it's fine since you're protected by the writer lock...

> + cnt += snprintf(&buf[cnt], KSYM_FILTER_ENTRY_LEN - cnt, "%s:",
> + entry->ksym_hbp->info.name);
> + if (entry->ksym_hbp->info.type == HW_BREAKPOINT_WRITE)
> + cnt += snprintf(&buf[cnt], KSYM_FILTER_ENTRY_LEN - cnt,
> + "-w-\n");
> + else if (entry->ksym_hbp->info.type == HW_BREAKPOINT_RW)
> + cnt += snprintf(&buf[cnt], KSYM_FILTER_ENTRY_LEN - cnt,
> + "rw-\n");
> + }
> + ret = simple_read_from_buffer(ubuf, count, ppos, buf, strlen(buf));
> + mutex_unlock(&ksym_tracer_mutex);
> +
> + return ret;
> +}
> +
> +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;
> +
> + /* Ignore echo "" > ksym_trace_filter */
> + if (count == 0)
> + return 0;
> +
> + input_string = kzalloc(count, GFP_KERNEL);
> + if (!input_string)
> + return -ENOMEM;
> +
> + if (copy_from_user(input_string, buffer, count)) {
> + kfree(input_string);
> + return -EFAULT;
> + }
> +
> + 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) {

Same here, ok...

> + if (entry->ksym_addr == ksym_addr) {
> + /* Check for malformed request: (6) */
> + if (entry->ksym_hbp->info.type != op)
> + changed = 1;
> + else
> + goto err_ret;
> + break;
> + }
> + }
> + if (changed) {
> + unregister_kernel_hw_breakpoint(entry->ksym_hbp);
> + entry->ksym_hbp->info.type = op;
> + if (op > 0) {
> + ret = register_kernel_hw_breakpoint(entry->ksym_hbp);
> + if (ret == 0) {
> + ret = count;
> + goto unlock_ret_path;
> + }
> + }
> + ksym_filter_entry_count--;
> + hlist_del_rcu(&(entry->ksym_hlist));
> + synchronize_rcu();
> + kfree(entry->ksym_hbp);
> + kfree(entry);
> + ret = count;
> + goto err_ret;
> + } else {
> + /* Check for malformed request: (4) */
> + if (op == 0)
> + goto err_ret;
> + ret = process_new_ksym_entry(ksymname, op, ksym_addr);
> + if (ret)
> + goto err_ret;
> + }
> + ret = count;
> + goto unlock_ret_path;
> +
> +err_ret:
> + kfree(input_string);
> +
> +unlock_ret_path:
> + mutex_unlock(&ksym_tracer_mutex);
> + 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)
> +{
> + struct trace_ksym *entry;
> + struct hlist_node *node, *node1;
> +
> + ksym_tracing_enabled = 0;
> +
> + mutex_lock(&ksym_tracer_mutex);
> + hlist_for_each_entry_safe(entry, node, node1, &ksym_filter_head,
> + ksym_hlist) {
> + unregister_kernel_hw_breakpoint(entry->ksym_hbp);
> + ksym_filter_entry_count--;
> + hlist_del_rcu(&(entry->ksym_hlist));
> + synchronize_rcu();
> + /* Free the 'input_string' only if reset
> + * after startup self-test
> + */
> +#ifdef CONFIG_FTRACE_SELFTEST
> + if (strncmp(entry->ksym_hbp->info.name, KSYM_SELFTEST_ENTRY,
> + strlen(KSYM_SELFTEST_ENTRY)) != 0)
> +#endif /* CONFIG_FTRACE_SELFTEST*/
> + kfree(entry->ksym_hbp->info.name);
> + kfree(entry->ksym_hbp);
> + kfree(entry);
> + }
> + mutex_unlock(&ksym_tracer_mutex);
> +}
> +
> +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;
> +
> +#ifdef CONFIG_FTRACE_SELFTEST
> + /* Check if we are re-entering self-test code during initialisation */
> + if (ksym_selftest_dummy)
> + goto ret_path;
> +
> + ksym_selftest_dummy = 0;
> +
> + /* Register the read-write tracing request */
> + ret = process_new_ksym_entry(KSYM_SELFTEST_ENTRY, HW_BREAKPOINT_RW,
> + (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++;
> +ret_path:
> +#endif /* CONFIG_FTRACE_SELFTEST */

It means that each time your tracer is selected, it will perform a selftest.
I think we only need this selftest once during the boot.
I would rather see that in the real selftest callback (trace_selftest_startup_kysm).

> +
> + 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 trace_ksym *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, "%-15s %-5d %-3d %-20s ", field->p_name,
> + entry->pid, iter->cpu, field->ksym_name);
> + if (!ret)
> + return TRACE_TYPE_PARTIAL_LINE;
> +
> + switch (field->ksym_hbp->info.type) {
> + case HW_BREAKPOINT_WRITE:
> + ret = trace_seq_printf(s, " W ");
> + break;
> + case HW_BREAKPOINT_RW:
> + 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, "%-20s\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", 0666, d_tracer,

Still writeable for everyone?

Thanks,
Frederic.

> + 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_printf(m, " Access type ");
> + seq_printf(m, " Symbol Counter \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);
> +
> + if (entry->ksym_hbp)
> + access_type = entry->ksym_hbp->info.type;
> +
> + switch (access_type) {
> + case HW_BREAKPOINT_WRITE:
> + seq_printf(m, " W ");
> + break;
> + case HW_BREAKPOINT_RW:
> + seq_printf(m, " RW ");
> + break;
> + default:
> + seq_printf(m, " NA ");
> + }
> +
> + if (lookup_symbol_name(entry->ksym_addr, fn_name) >= 0)
> + seq_printf(m, " %s ", fn_name);
> + else
> + seq_printf(m, " <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 */
> Index: kernel/trace/trace_selftest.c
> ===================================================================
> --- kernel/trace/trace_selftest.c.orig
> +++ kernel/trace/trace_selftest.c
> @@ -17,6 +17,7 @@ static inline int trace_valid_entry(stru
> case TRACE_GRAPH_ENT:
> case TRACE_GRAPH_RET:
> case TRACE_HW_BRANCHES:
> + case TRACE_KSYM:
> return 1;
> }
> return 0;
> @@ -807,3 +808,39 @@ trace_selftest_startup_hw_branches(struc
> return ret;
> }
> #endif /* CONFIG_HW_BRANCH_TRACER */
> +
> +#ifdef CONFIG_KSYM_TRACER
> +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;
> + }
> +
> + /* Sleep for a 1/10 of a second */
> + msleep(100);
> + /* 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;
> + }
> +
> + return ret;
> +}
> +#endif /* CONFIG_KSYM_TRACER */
> +
>