/*
* Copyright (C) 2008 Mathieu Desnoyers
*
* 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.
*/
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/types.h>
#include <linux/jhash.h>
#include <linux/list.h>
#include <linux/rcupdate.h>
#include <linux/tracepoint.h>
#include <linux/err.h>
#include <linux/slab.h>
extern struct tracepoint __start___tracepoints[];
extern struct tracepoint __stop___tracepoints[];
/* Set to 1 to enable tracepoint debug output */
static const int tracepoint_debug;
/*
* tracepoints_mutex nests inside module_mutex. Tracepoints mutex protects the
* builtin and module tracepoints and the hash table.
*/
static DEFINE_MUTEX(tracepoints_mutex);
/*
* Tracepoint hash table, containing the active tracepoints.
* Protected by tracepoints_mutex.
*/
#define TRACEPOINT_HASH_BITS 6
#define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)
/*
* Note about RCU :
* It is used to to delay the free of multiple probes array until a quiescent
* state is reached.
* Tracepoint entries modifications are protected by the tracepoints_mutex.
*/
struct tracepoint_entry {
struct hlist_node hlist;
void **funcs;
int refcount; /* Number of times armed. 0 if disarmed. */
struct rcu_head rcu;
void *oldptr;
unsigned char rcu_pending:1;
char name[0];
};
static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
static void free_old_closure(struct rcu_head *head)
{
struct tracepoint_entry *entry = container_of(head,
struct tracepoint_entry, rcu);
kfree(entry->oldptr);
/* Make sure we free the data before setting the pending flag to 0 */
smp_wmb();
entry->rcu_pending = 0;
}
static void tracepoint_entry_free_old(struct tracepoint_entry *entry, void *old)
{
if (!old)
return;
entry->oldptr = old;
entry->rcu_pending = 1;
/* write rcu_pending before calling the RCU callback */
smp_wmb();
#ifdef CONFIG_PREEMPT_RCU
synchronize_sched(); /* Until we have the call_rcu_sched() */
#endif
call_rcu(&entry->rcu, free_old_closure);
}
static void debug_print_probes(struct tracepoint_entry *entry)
{
int i;
if (!tracepoint_debug)
return;
for (i = 0; entry->funcs[i]; i++)
printk(KERN_DEBUG "Probe %d : %p\n", i, entry->funcs[i]);
}
static void *
tracepoint_entry_add_probe(struct tracepoint_entry *entry, void *probe)
{
int nr_probes = 0;
void **old, **new;
WARN_ON(!probe);
debug_print_probes(entry);
old = entry->funcs;
if (old) {
/* (N -> N+1), (N != 0, 1) probes */
for (nr_probes = 0; old[nr_probes]; nr_probes++)
if (old[nr_probes] == probe)
return ERR_PTR(-EEXIST);
}
/* + 2 : one for new probe, one for NULL func */
new = kzalloc((nr_probes + 2) * sizeof(void *), GFP_KERNEL);
if (new == NULL)
return ERR_PTR(-ENOMEM);
if (old)
memcpy(new, old, nr_probes * sizeof(void *));
new[nr_probes] = probe;
entry->refcount = nr_probes + 1;
entry->funcs = new;
debug_print_probes(entry);
return old;
}
static void *
tracepoint_entry_remove_probe(struct tracepoint_entry *entry, void *probe)
{
int nr_probes = 0, nr_del = 0, i;
void **old, **new;
old = entry->funcs;
debug_print_probes(entry);
/* (N -> M), (N > 1, M >= 0) probes */
for (nr_probes = 0; old[nr_probes]; nr_probes++) {
if ((!probe || old[nr_probes] == probe))
nr_del++;
}
if (nr_probes - nr_del == 0) {
/* N -> 0, (N > 1) */
entry->funcs = NULL;
entry->refcount = 0;
debug_print_probes(entry);
return old;
} else {
int j = 0;
/* N -> M, (N > 1, M > 0) */
/* + 1 for NULL */
new = kzalloc((nr_probes - nr_del + 1)
* sizeof(void *), GFP_KERNEL);
if (new == NULL)
return ERR_PTR(-ENOMEM);
for (i = 0; old[i]; i++)
if ((probe && old[i] != probe))
new[j++] = old[i];
entry->refcount = nr_probes - nr_del;
entry->funcs = new;
}
debug_print_probes(entry);
return old;
}
/*
* Get tracepoint if the tracepoint is present in the tracepoint hash table.
* Must be called with tracepoints_mutex held.
* Returns NULL if not present.
*/
static struct tracepoint_entry *get_tracepoint(const char *name)
{
struct hlist_head *head;
struct hlist_node *node;
struct tracepoint_entry *e;
u32 hash = jhash(name, strlen(name), 0);
head = &tracepoint_table[hash & ((1 << TRACEPOINT_HASH_BITS)-1)];
hlist_for_each_entry(e, node, head, hlist) {
if (!strcmp(name, e->name))
return e;
}
return NULL;
}
/*
* Add the tracepoint to the tracepoint hash table. Must be called with
* tracepoints_mutex held.
*/
static struct tracepoint_entry *add_tracepoint(const char *name)
{
struct hlist_head *head;
struct hlist_node *node;
struct tracepoint_entry *e;
size_t name_len = strlen(name) + 1;
u32 hash = jhash(name, name_len-1, 0);
head = &tracepoint_table[hash & ((1 << TRACEPOINT_HASH_BITS)-1)];
hlist_for_each_entry(e, node, head, hlist) {
if (!strcmp(name, e->name)) {
printk(KERN_NOTICE
"tracepoint %s busy\n", name);
return ERR_PTR(-EEXIST); /* Already there */
}
}
/*
* Using kmalloc here to allocate a variable length element. Could
* cause some memory fragmentation if overused.
*/
e = kmalloc(sizeof(struct tracepoint_entry) + name_len, GFP_KERNEL);
if (!e)
return ERR_PTR(-ENOMEM);
memcpy(&e->name[0], name, name_len);
e->funcs = NULL;
e->refcount = 0;
e->rcu_pending = 0;
hlist_add_head(&e->hlist, head);
return e;
}
/*
* Remove the tracepoint from the tracepoint hash table. Must be called with
* mutex_lock held.
*/
static int remove_tracepoint(const char *name)
{
struct hlist_head *head;
struct hlist_node *node;
struct tracepoint_entry *e;
int found = 0;
size_t len = strlen(name) + 1;
u32 hash = jhash(name, len-1, 0);
head = &tracepoint_table[hash & ((1 << TRACEPOINT_HASH_BITS)-1)];
hlist_for_each_entry(e, node, head, hlist) {
if (!strcmp(name, e->name)) {
found = 1;
break;
}
}
if (!found)
return -ENOENT;
if (e->refcount)
return -EBUSY;
hlist_del(&e->hlist);
/* Make sure the call_rcu has been executed */
if (e->rcu_pending)
rcu_barrier();
kfree(e);
return 0;
}
/*
* Sets the probe callback corresponding to one tracepoint.
*/
static void set_tracepoint(struct tracepoint_entry **entry,
struct tracepoint *elem, int active)
{
WARN_ON(strcmp((*entry)->name, elem->name) != 0);
/*
* rcu_assign_pointer has a smp_wmb() which makes sure that the new
* probe callbacks array is consistent before setting a pointer to it.
* This array is referenced by __DO_TRACE from
* include/linux/tracepoints.h. A matching smp_read_barrier_depends()
* is used.
*/
rcu_assign_pointer(elem->funcs, (*entry)->funcs);
elem->state = active;
}
/*
* Disable a tracepoint and its probe callback.
* Note: only waiting an RCU period after setting elem->call to the empty
* function insures that the original callback is not used anymore. This insured
* by preempt_disable around the call site.
*/
static void disable_tracepoint(struct tracepoint *elem)
{
elem->state = 0;
}
/**
* tracepoint_update_probe_range - Update a probe range
* @begin: beginning of the range
* @end: end of the range
*
* Updates the probe callback corresponding to a range of tracepoints.
*/
void tracepoint_update_probe_range(struct tracepoint *begin,
struct tracepoint *end)
{
struct tracepoint *iter;
struct tracepoint_entry *mark_entry;
mutex_lock(&tracepoints_mutex);
for (iter = begin; iter < end; iter++) {
mark_entry = get_tracepoint(iter->name);
if (mark_entry) {
set_tracepoint(&mark_entry, iter,
!!mark_entry->refcount);
} else {
disable_tracepoint(iter);
}
}
mutex_unlock(&tracepoints_mutex);
}
/*
* Update probes, removing the faulty probes.
*/
static void tracepoint_update_probes(void)
{
/* Core kernel tracepoints */
tracepoint_update_probe_range(__start___tracepoints,
__stop___tracepoints);
/* tracepoints in modules. */
module_update_tracepoints();
}
/**
* tracepoint_probe_register - Connect a probe to a tracepoint
* @name: tracepoint name
* @probe: probe handler
*
* Returns 0 if ok, error value on error.
* The probe address must at least be aligned on the architecture pointer size.
*/
int tracepoint_probe_register(const char *name, void *probe)
{
struct tracepoint_entry *entry;
int ret = 0;
void *old;
mutex_lock(&tracepoints_mutex);
entry = get_tracepoint(name);
if (!entry) {
entry = add_tracepoint(name);
if (IS_ERR(entry)) {
ret = PTR_ERR(entry);
goto end;
}
}
/*
* If we detect that a call_rcu is pending for this tracepoint,
* make sure it's executed now.
*/
if (entry->rcu_pending)
rcu_barrier();
old = tracepoint_entry_add_probe(entry, probe);
if (IS_ERR(old)) {
ret = PTR_ERR(old);
goto end;
}
mutex_unlock(&tracepoints_mutex);
tracepoint_update_probes(); /* may update entry */
mutex_lock(&tracepoints_mutex);
entry = get_tracepoint(name);
WARN_ON(!entry);
tracepoint_entry_free_old(entry, old);
end:
mutex_unlock(&tracepoints_mutex);
return ret;
}
EXPORT_SYMBOL_GPL(tracepoint_probe_register);
/**
* tracepoint_probe_unregister - Disconnect a probe from a tracepoint
* @name: tracepoint name
* @probe: probe function pointer
*
* We do not need to call a synchronize_sched to make sure the probes have
* finished running before doing a module unload, because the module unload
* itself uses stop_machine(), which insures that every preempt disabled section
* have finished.
*/
int tracepoint_probe_unregister(const char *name, void *probe)
{
struct tracepoint_entry *entry;
void *old;
int ret = -ENOENT;
mutex_lock(&tracepoints_mutex);
entry = get_tracepoint(name);
if (!entry)
goto end;
if (entry->rcu_pending)
rcu_barrier();
old = tracepoint_entry_remove_probe(entry, probe);
mutex_unlock(&tracepoints_mutex);
tracepoint_update_probes(); /* may update entry */
mutex_lock(&tracepoints_mutex);
entry = get_tracepoint(name);
if (!entry)
goto end;
tracepoint_entry_free_old(entry, old);
remove_tracepoint(name); /* Ignore busy error message */
ret = 0;
end:
mutex_unlock(&tracepoints_mutex);
return ret;
}
EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
/**
* tracepoint_get_iter_range - Get a next tracepoint iterator given a range.
* @tracepoint: current tracepoints (in), next tracepoint (out)
* @begin: beginning of the range
* @end: end of the range
*
* Returns whether a next tracepoint has been found (1) or not (0).
* Will return the first tracepoint in the range if the input tracepoint is
* NULL.
*/
int tracepoint_get_iter_range(struct tracepoint **tracepoint,
struct tracepoint *begin, struct tracepoint *end)
{
if (!*tracepoint && begin != end) {
*tracepoint = begin;
return 1;
}
if (*tracepoint >= begin && *tracepoint < end)
return 1;
return 0;
}
EXPORT_SYMBOL_GPL(tracepoint_get_iter_range);
static void tracepoint_get_iter(struct tracepoint_iter *iter)
{
int found = 0;
/* Core kernel tracepoints */
if (!iter->module) {
found = tracepoint_get_iter_range(&iter->tracepoint,
__start___tracepoints, __stop___tracepoints);
if (found)
goto end;
}
/* tracepoints in modules. */
found = module_get_iter_tracepoints(iter);
end:
if (!found)
tracepoint_iter_reset(iter);
}
void tracepoint_iter_start(struct tracepoint_iter *iter)
{
tracepoint_get_iter(iter);
}
EXPORT_SYMBOL_GPL(tracepoint_iter_start);
void tracepoint_iter_next(struct tracepoint_iter *iter)
{
iter->tracepoint++;
/*
* iter->tracepoint may be invalid because we blindly incremented it.
* Make sure it is valid by marshalling on the tracepoints, getting the
* tracepoints from following modules if necessary.
*/
tracepoint_get_iter(iter);
}
EXPORT_SYMBOL_GPL(tracepoint_iter_next);
void tracepoint_iter_stop(struct tracepoint_iter *iter)
{
}
EXPORT_SYMBOL_GPL(tracepoint_iter_stop);
void tracepoint_iter_reset(struct tracepoint_iter *iter)
{
iter->module = NULL;
iter->tracepoint = NULL;
}
EXPORT_SYMBOL_GPL(tracepoint_iter_reset);
