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ftrace: Convert graph filter to use hash tables
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Use ftrace_hash instead of a static array of a fixed size.  This is
useful when a graph filter pattern matches to a large number of
functions.  Now hash lookup is done with preemption disabled to protect
from the hash being changed/freed.

Link: http://lkml.kernel.org/r/20170120024447.26097-3-namhyung@kernel.org

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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Namhyung Kim authored and Steven Rostedt (VMware) committed Jan 20, 2017
1 parent 4046bf0 commit b9b0c83
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Showing 2 changed files with 158 additions and 96 deletions.
190 changes: 127 additions & 63 deletions kernel/trace/ftrace.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4378,7 +4378,7 @@ __setup("ftrace_filter=", set_ftrace_filter);
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
static char ftrace_graph_buf[FTRACE_FILTER_SIZE] __initdata;
static char ftrace_graph_notrace_buf[FTRACE_FILTER_SIZE] __initdata;
static int ftrace_set_func(unsigned long *array, int *idx, int size, char *buffer);
static int ftrace_graph_set_hash(struct ftrace_hash *hash, char *buffer);

static unsigned long save_global_trampoline;
static unsigned long save_global_flags;
Expand All @@ -4401,18 +4401,17 @@ static void __init set_ftrace_early_graph(char *buf, int enable)
{
int ret;
char *func;
unsigned long *table = ftrace_graph_funcs;
int *count = &ftrace_graph_count;
struct ftrace_hash *hash;

if (!enable) {
table = ftrace_graph_notrace_funcs;
count = &ftrace_graph_notrace_count;
}
if (enable)
hash = ftrace_graph_hash;
else
hash = ftrace_graph_notrace_hash;

while (buf) {
func = strsep(&buf, ",");
/* we allow only one expression at a time */
ret = ftrace_set_func(table, count, FTRACE_GRAPH_MAX_FUNCS, func);
ret = ftrace_graph_set_hash(hash, func);
if (ret)
printk(KERN_DEBUG "ftrace: function %s not "
"traceable\n", func);
Expand Down Expand Up @@ -4536,26 +4535,52 @@ static const struct file_operations ftrace_notrace_fops = {

static DEFINE_MUTEX(graph_lock);

int ftrace_graph_count;
int ftrace_graph_notrace_count;
unsigned long ftrace_graph_funcs[FTRACE_GRAPH_MAX_FUNCS] __read_mostly;
unsigned long ftrace_graph_notrace_funcs[FTRACE_GRAPH_MAX_FUNCS] __read_mostly;
struct ftrace_hash *ftrace_graph_hash = EMPTY_HASH;
struct ftrace_hash *ftrace_graph_notrace_hash = EMPTY_HASH;

enum graph_filter_type {
GRAPH_FILTER_NOTRACE = 0,
GRAPH_FILTER_FUNCTION,
};

struct ftrace_graph_data {
unsigned long *table;
size_t size;
int *count;
struct ftrace_hash *hash;
struct ftrace_func_entry *entry;
int idx; /* for hash table iteration */
enum graph_filter_type type;
struct ftrace_hash *new_hash;
const struct seq_operations *seq_ops;
};

static void *
__g_next(struct seq_file *m, loff_t *pos)
{
struct ftrace_graph_data *fgd = m->private;
struct ftrace_func_entry *entry = fgd->entry;
struct hlist_head *head;
int i, idx = fgd->idx;

if (*pos >= *fgd->count)
if (*pos >= fgd->hash->count)
return NULL;
return &fgd->table[*pos];

if (entry) {
hlist_for_each_entry_continue(entry, hlist) {
fgd->entry = entry;
return entry;
}

idx++;
}

for (i = idx; i < 1 << fgd->hash->size_bits; i++) {
head = &fgd->hash->buckets[i];
hlist_for_each_entry(entry, head, hlist) {
fgd->entry = entry;
fgd->idx = i;
return entry;
}
}
return NULL;
}

static void *
Expand All @@ -4572,9 +4597,11 @@ static void *g_start(struct seq_file *m, loff_t *pos)
mutex_lock(&graph_lock);

/* Nothing, tell g_show to print all functions are enabled */
if (!*fgd->count && !*pos)
if (ftrace_hash_empty(fgd->hash) && !*pos)
return (void *)1;

fgd->idx = 0;
fgd->entry = NULL;
return __g_next(m, pos);
}

Expand All @@ -4585,22 +4612,22 @@ static void g_stop(struct seq_file *m, void *p)

static int g_show(struct seq_file *m, void *v)
{
unsigned long *ptr = v;
struct ftrace_func_entry *entry = v;

if (!ptr)
if (!entry)
return 0;

if (ptr == (unsigned long *)1) {
if (entry == (void *)1) {
struct ftrace_graph_data *fgd = m->private;

if (fgd->table == ftrace_graph_funcs)
if (fgd->type == GRAPH_FILTER_FUNCTION)
seq_puts(m, "#### all functions enabled ####\n");
else
seq_puts(m, "#### no functions disabled ####\n");
return 0;
}

seq_printf(m, "%ps\n", (void *)*ptr);
seq_printf(m, "%ps\n", (void *)entry->ip);

return 0;
}
Expand All @@ -4617,31 +4644,45 @@ __ftrace_graph_open(struct inode *inode, struct file *file,
struct ftrace_graph_data *fgd)
{
int ret = 0;
struct ftrace_hash *new_hash = NULL;

mutex_lock(&graph_lock);
if ((file->f_mode & FMODE_WRITE) &&
(file->f_flags & O_TRUNC)) {
*fgd->count = 0;
memset(fgd->table, 0, fgd->size * sizeof(*fgd->table));
if (file->f_mode & FMODE_WRITE) {
const int size_bits = FTRACE_HASH_DEFAULT_BITS;

if (file->f_flags & O_TRUNC)
new_hash = alloc_ftrace_hash(size_bits);
else
new_hash = alloc_and_copy_ftrace_hash(size_bits,
fgd->hash);
if (!new_hash) {
ret = -ENOMEM;
goto out;
}
}
mutex_unlock(&graph_lock);

if (file->f_mode & FMODE_READ) {
ret = seq_open(file, fgd->seq_ops);
ret = seq_open(file, &ftrace_graph_seq_ops);
if (!ret) {
struct seq_file *m = file->private_data;
m->private = fgd;
} else {
/* Failed */
free_ftrace_hash(new_hash);
new_hash = NULL;
}
} else
file->private_data = fgd;

out:
fgd->new_hash = new_hash;
return ret;
}

static int
ftrace_graph_open(struct inode *inode, struct file *file)
{
struct ftrace_graph_data *fgd;
int ret;

if (unlikely(ftrace_disabled))
return -ENODEV;
Expand All @@ -4650,18 +4691,25 @@ ftrace_graph_open(struct inode *inode, struct file *file)
if (fgd == NULL)
return -ENOMEM;

fgd->table = ftrace_graph_funcs;
fgd->size = FTRACE_GRAPH_MAX_FUNCS;
fgd->count = &ftrace_graph_count;
mutex_lock(&graph_lock);

fgd->hash = ftrace_graph_hash;
fgd->type = GRAPH_FILTER_FUNCTION;
fgd->seq_ops = &ftrace_graph_seq_ops;

return __ftrace_graph_open(inode, file, fgd);
ret = __ftrace_graph_open(inode, file, fgd);
if (ret < 0)
kfree(fgd);

mutex_unlock(&graph_lock);
return ret;
}

static int
ftrace_graph_notrace_open(struct inode *inode, struct file *file)
{
struct ftrace_graph_data *fgd;
int ret;

if (unlikely(ftrace_disabled))
return -ENODEV;
Expand All @@ -4670,45 +4718,53 @@ ftrace_graph_notrace_open(struct inode *inode, struct file *file)
if (fgd == NULL)
return -ENOMEM;

fgd->table = ftrace_graph_notrace_funcs;
fgd->size = FTRACE_GRAPH_MAX_FUNCS;
fgd->count = &ftrace_graph_notrace_count;
mutex_lock(&graph_lock);

fgd->hash = ftrace_graph_notrace_hash;
fgd->type = GRAPH_FILTER_NOTRACE;
fgd->seq_ops = &ftrace_graph_seq_ops;

return __ftrace_graph_open(inode, file, fgd);
ret = __ftrace_graph_open(inode, file, fgd);
if (ret < 0)
kfree(fgd);

mutex_unlock(&graph_lock);
return ret;
}

static int
ftrace_graph_release(struct inode *inode, struct file *file)
{
struct ftrace_graph_data *fgd;

if (file->f_mode & FMODE_READ) {
struct seq_file *m = file->private_data;

kfree(m->private);
fgd = m->private;
seq_release(inode, file);
} else {
kfree(file->private_data);
fgd = file->private_data;
}

kfree(fgd->new_hash);
kfree(fgd);

return 0;
}

static int
ftrace_set_func(unsigned long *array, int *idx, int size, char *buffer)
ftrace_graph_set_hash(struct ftrace_hash *hash, char *buffer)
{
struct ftrace_glob func_g;
struct dyn_ftrace *rec;
struct ftrace_page *pg;
struct ftrace_func_entry *entry;
int fail = 1;
int not;
bool exists;
int i;

/* decode regex */
func_g.type = filter_parse_regex(buffer, strlen(buffer),
&func_g.search, &not);
if (!not && *idx >= size)
return -EBUSY;

func_g.len = strlen(func_g.search);

Expand All @@ -4725,26 +4781,18 @@ ftrace_set_func(unsigned long *array, int *idx, int size, char *buffer)
continue;

if (ftrace_match_record(rec, &func_g, NULL, 0)) {
/* if it is in the array */
exists = false;
for (i = 0; i < *idx; i++) {
if (array[i] == rec->ip) {
exists = true;
break;
}
}
entry = ftrace_lookup_ip(hash, rec->ip);

if (!not) {
fail = 0;
if (!exists) {
array[(*idx)++] = rec->ip;
if (*idx >= size)
goto out;
}

if (entry)
continue;
if (add_hash_entry(hash, rec->ip) < 0)
goto out;
} else {
if (exists) {
array[i] = array[--(*idx)];
array[*idx] = 0;
if (entry) {
free_hash_entry(hash, entry);
fail = 0;
}
}
Expand All @@ -4766,6 +4814,7 @@ ftrace_graph_write(struct file *file, const char __user *ubuf,
struct trace_parser parser;
ssize_t read, ret = 0;
struct ftrace_graph_data *fgd = file->private_data;
struct ftrace_hash *old_hash, *new_hash;

if (!cnt)
return 0;
Expand All @@ -4781,10 +4830,25 @@ ftrace_graph_write(struct file *file, const char __user *ubuf,
mutex_lock(&graph_lock);

/* we allow only one expression at a time */
ret = ftrace_set_func(fgd->table, fgd->count, fgd->size,
parser.buffer);
ret = ftrace_graph_set_hash(fgd->new_hash,
parser.buffer);

old_hash = fgd->hash;
new_hash = __ftrace_hash_move(fgd->new_hash);
if (!new_hash)
ret = -ENOMEM;

if (fgd->type == GRAPH_FILTER_FUNCTION)
rcu_assign_pointer(ftrace_graph_hash, new_hash);
else
rcu_assign_pointer(ftrace_graph_notrace_hash, new_hash);

mutex_unlock(&graph_lock);

/* Wait till all users are no longer using the old hash */
synchronize_sched();

free_ftrace_hash(old_hash);
}

if (!ret)
Expand Down
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