linux-stable/kernel/tracepoint.c
Mathieu Desnoyers b75ef8b44b Tracepoint: Dissociate from module mutex
Copy the information needed from struct module into a local module list
held within tracepoint.c from within the module coming/going notifier.

This vastly simplifies locking of tracepoint registration /
unregistration, because we don't have to take the module mutex to
register and unregister tracepoints anymore. Steven Rostedt ran into
dependency problems related to modules mutex vs kprobes mutex vs ftrace
mutex vs tracepoint mutex that seems to be hard to fix without removing
this dependency between tracepoint and module mutex. (note: it should be
investigated whether kprobes could benefit of being dissociated from the
modules mutex too.)

This also fixes module handling of tracepoint list iterators, because it
was expecting the list to be sorted by pointer address. Given we have
control on our own list now, it's OK to sort this list which has
tracepoints as its only purpose. The reason why this sorting is required
is to handle the fact that seq files (and any read() operation from
user-space) cannot hold the tracepoint mutex across multiple calls, so
list entries may vanish between calls. With sorting, the tracepoint
iterator becomes usable even if the list don't contain the exact item
pointed to by the iterator anymore.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Jason Baron <jbaron@redhat.com>
CC: Ingo Molnar <mingo@elte.hu>
CC: Lai Jiangshan <laijs@cn.fujitsu.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Link: http://lkml.kernel.org/r/20110810191839.GC8525@Krystal
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2011-08-10 20:38:14 -04:00

765 lines
20 KiB
C

/*
* 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>
#include <linux/sched.h>
#include <linux/jump_label.h>
extern struct tracepoint * const __start___tracepoints_ptrs[];
extern struct tracepoint * const __stop___tracepoints_ptrs[];
/* Set to 1 to enable tracepoint debug output */
static const int tracepoint_debug;
/*
* Tracepoints mutex protects the builtin and module tracepoints and the hash
* table, as well as the local module list.
*/
static DEFINE_MUTEX(tracepoints_mutex);
#ifdef CONFIG_MODULES
/* Local list of struct module */
static LIST_HEAD(tracepoint_module_list);
#endif /* CONFIG_MODULES */
/*
* Tracepoint hash table, containing the active tracepoints.
* Protected by tracepoints_mutex.
*/
#define TRACEPOINT_HASH_BITS 6
#define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)
static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
/*
* Note about RCU :
* It is used 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;
struct tracepoint_func *funcs;
int refcount; /* Number of times armed. 0 if disarmed. */
char name[0];
};
struct tp_probes {
union {
struct rcu_head rcu;
struct list_head list;
} u;
struct tracepoint_func probes[0];
};
static inline void *allocate_probes(int count)
{
struct tp_probes *p = kmalloc(count * sizeof(struct tracepoint_func)
+ sizeof(struct tp_probes), GFP_KERNEL);
return p == NULL ? NULL : p->probes;
}
static void rcu_free_old_probes(struct rcu_head *head)
{
kfree(container_of(head, struct tp_probes, u.rcu));
}
static inline void release_probes(struct tracepoint_func *old)
{
if (old) {
struct tp_probes *tp_probes = container_of(old,
struct tp_probes, probes[0]);
call_rcu_sched(&tp_probes->u.rcu, rcu_free_old_probes);
}
}
static void debug_print_probes(struct tracepoint_entry *entry)
{
int i;
if (!tracepoint_debug || !entry->funcs)
return;
for (i = 0; entry->funcs[i].func; i++)
printk(KERN_DEBUG "Probe %d : %p\n", i, entry->funcs[i].func);
}
static struct tracepoint_func *
tracepoint_entry_add_probe(struct tracepoint_entry *entry,
void *probe, void *data)
{
int nr_probes = 0;
struct tracepoint_func *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].func; nr_probes++)
if (old[nr_probes].func == probe &&
old[nr_probes].data == data)
return ERR_PTR(-EEXIST);
}
/* + 2 : one for new probe, one for NULL func */
new = allocate_probes(nr_probes + 2);
if (new == NULL)
return ERR_PTR(-ENOMEM);
if (old)
memcpy(new, old, nr_probes * sizeof(struct tracepoint_func));
new[nr_probes].func = probe;
new[nr_probes].data = data;
new[nr_probes + 1].func = NULL;
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, void *data)
{
int nr_probes = 0, nr_del = 0, i;
struct tracepoint_func *old, *new;
old = entry->funcs;
if (!old)
return ERR_PTR(-ENOENT);
debug_print_probes(entry);
/* (N -> M), (N > 1, M >= 0) probes */
for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
if (!probe ||
(old[nr_probes].func == probe &&
old[nr_probes].data == data))
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 = allocate_probes(nr_probes - nr_del + 1);
if (new == NULL)
return ERR_PTR(-ENOMEM);
for (i = 0; old[i].func; i++)
if (probe &&
(old[i].func != probe || old[i].data != data))
new[j++] = old[i];
new[nr_probes - nr_del].func = NULL;
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 & (TRACEPOINT_TABLE_SIZE - 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 & (TRACEPOINT_TABLE_SIZE - 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;
hlist_add_head(&e->hlist, head);
return e;
}
/*
* Remove the tracepoint from the tracepoint hash table. Must be called with
* mutex_lock held.
*/
static inline void remove_tracepoint(struct tracepoint_entry *e)
{
hlist_del(&e->hlist);
kfree(e);
}
/*
* 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);
if (elem->regfunc && !jump_label_enabled(&elem->key) && active)
elem->regfunc();
else if (elem->unregfunc && jump_label_enabled(&elem->key) && !active)
elem->unregfunc();
/*
* 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);
if (active && !jump_label_enabled(&elem->key))
jump_label_inc(&elem->key);
else if (!active && jump_label_enabled(&elem->key))
jump_label_dec(&elem->key);
}
/*
* 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)
{
if (elem->unregfunc && jump_label_enabled(&elem->key))
elem->unregfunc();
if (jump_label_enabled(&elem->key))
jump_label_dec(&elem->key);
rcu_assign_pointer(elem->funcs, NULL);
}
/**
* 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.
* Called with tracepoints_mutex held.
*/
static void tracepoint_update_probe_range(struct tracepoint * const *begin,
struct tracepoint * const *end)
{
struct tracepoint * const *iter;
struct tracepoint_entry *mark_entry;
if (!begin)
return;
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);
}
}
}
#ifdef CONFIG_MODULES
void module_update_tracepoints(void)
{
struct tp_module *tp_mod;
list_for_each_entry(tp_mod, &tracepoint_module_list, list)
tracepoint_update_probe_range(tp_mod->tracepoints_ptrs,
tp_mod->tracepoints_ptrs + tp_mod->num_tracepoints);
}
#else /* CONFIG_MODULES */
void module_update_tracepoints(void)
{
}
#endif /* CONFIG_MODULES */
/*
* Update probes, removing the faulty probes.
* Called with tracepoints_mutex held.
*/
static void tracepoint_update_probes(void)
{
/* Core kernel tracepoints */
tracepoint_update_probe_range(__start___tracepoints_ptrs,
__stop___tracepoints_ptrs);
/* tracepoints in modules. */
module_update_tracepoints();
}
static struct tracepoint_func *
tracepoint_add_probe(const char *name, void *probe, void *data)
{
struct tracepoint_entry *entry;
struct tracepoint_func *old;
entry = get_tracepoint(name);
if (!entry) {
entry = add_tracepoint(name);
if (IS_ERR(entry))
return (struct tracepoint_func *)entry;
}
old = tracepoint_entry_add_probe(entry, probe, data);
if (IS_ERR(old) && !entry->refcount)
remove_tracepoint(entry);
return old;
}
/**
* 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, void *data)
{
struct tracepoint_func *old;
mutex_lock(&tracepoints_mutex);
old = tracepoint_add_probe(name, probe, data);
if (IS_ERR(old)) {
mutex_unlock(&tracepoints_mutex);
return PTR_ERR(old);
}
tracepoint_update_probes(); /* may update entry */
mutex_unlock(&tracepoints_mutex);
release_probes(old);
return 0;
}
EXPORT_SYMBOL_GPL(tracepoint_probe_register);
static struct tracepoint_func *
tracepoint_remove_probe(const char *name, void *probe, void *data)
{
struct tracepoint_entry *entry;
struct tracepoint_func *old;
entry = get_tracepoint(name);
if (!entry)
return ERR_PTR(-ENOENT);
old = tracepoint_entry_remove_probe(entry, probe, data);
if (IS_ERR(old))
return old;
if (!entry->refcount)
remove_tracepoint(entry);
return old;
}
/**
* 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, void *data)
{
struct tracepoint_func *old;
mutex_lock(&tracepoints_mutex);
old = tracepoint_remove_probe(name, probe, data);
if (IS_ERR(old)) {
mutex_unlock(&tracepoints_mutex);
return PTR_ERR(old);
}
tracepoint_update_probes(); /* may update entry */
mutex_unlock(&tracepoints_mutex);
release_probes(old);
return 0;
}
EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
static LIST_HEAD(old_probes);
static int need_update;
static void tracepoint_add_old_probes(void *old)
{
need_update = 1;
if (old) {
struct tp_probes *tp_probes = container_of(old,
struct tp_probes, probes[0]);
list_add(&tp_probes->u.list, &old_probes);
}
}
/**
* tracepoint_probe_register_noupdate - register a probe but not connect
* @name: tracepoint name
* @probe: probe handler
*
* caller must call tracepoint_probe_update_all()
*/
int tracepoint_probe_register_noupdate(const char *name, void *probe,
void *data)
{
struct tracepoint_func *old;
mutex_lock(&tracepoints_mutex);
old = tracepoint_add_probe(name, probe, data);
if (IS_ERR(old)) {
mutex_unlock(&tracepoints_mutex);
return PTR_ERR(old);
}
tracepoint_add_old_probes(old);
mutex_unlock(&tracepoints_mutex);
return 0;
}
EXPORT_SYMBOL_GPL(tracepoint_probe_register_noupdate);
/**
* tracepoint_probe_unregister_noupdate - remove a probe but not disconnect
* @name: tracepoint name
* @probe: probe function pointer
*
* caller must call tracepoint_probe_update_all()
*/
int tracepoint_probe_unregister_noupdate(const char *name, void *probe,
void *data)
{
struct tracepoint_func *old;
mutex_lock(&tracepoints_mutex);
old = tracepoint_remove_probe(name, probe, data);
if (IS_ERR(old)) {
mutex_unlock(&tracepoints_mutex);
return PTR_ERR(old);
}
tracepoint_add_old_probes(old);
mutex_unlock(&tracepoints_mutex);
return 0;
}
EXPORT_SYMBOL_GPL(tracepoint_probe_unregister_noupdate);
/**
* tracepoint_probe_update_all - update tracepoints
*/
void tracepoint_probe_update_all(void)
{
LIST_HEAD(release_probes);
struct tp_probes *pos, *next;
mutex_lock(&tracepoints_mutex);
if (!need_update) {
mutex_unlock(&tracepoints_mutex);
return;
}
if (!list_empty(&old_probes))
list_replace_init(&old_probes, &release_probes);
need_update = 0;
tracepoint_update_probes();
mutex_unlock(&tracepoints_mutex);
list_for_each_entry_safe(pos, next, &release_probes, u.list) {
list_del(&pos->u.list);
call_rcu_sched(&pos->u.rcu, rcu_free_old_probes);
}
}
EXPORT_SYMBOL_GPL(tracepoint_probe_update_all);
/**
* 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.
*/
static int tracepoint_get_iter_range(struct tracepoint * const **tracepoint,
struct tracepoint * const *begin, struct tracepoint * const *end)
{
if (!*tracepoint && begin != end) {
*tracepoint = begin;
return 1;
}
if (*tracepoint >= begin && *tracepoint < end)
return 1;
return 0;
}
#ifdef CONFIG_MODULES
static void tracepoint_get_iter(struct tracepoint_iter *iter)
{
int found = 0;
struct tp_module *iter_mod;
/* Core kernel tracepoints */
if (!iter->module) {
found = tracepoint_get_iter_range(&iter->tracepoint,
__start___tracepoints_ptrs,
__stop___tracepoints_ptrs);
if (found)
goto end;
}
/* Tracepoints in modules */
mutex_lock(&tracepoints_mutex);
list_for_each_entry(iter_mod, &tracepoint_module_list, list) {
/*
* Sorted module list
*/
if (iter_mod < iter->module)
continue;
else if (iter_mod > iter->module)
iter->tracepoint = NULL;
found = tracepoint_get_iter_range(&iter->tracepoint,
iter_mod->tracepoints_ptrs,
iter_mod->tracepoints_ptrs
+ iter_mod->num_tracepoints);
if (found) {
iter->module = iter_mod;
break;
}
}
mutex_unlock(&tracepoints_mutex);
end:
if (!found)
tracepoint_iter_reset(iter);
}
#else /* CONFIG_MODULES */
static void tracepoint_get_iter(struct tracepoint_iter *iter)
{
int found = 0;
/* Core kernel tracepoints */
found = tracepoint_get_iter_range(&iter->tracepoint,
__start___tracepoints_ptrs,
__stop___tracepoints_ptrs);
if (!found)
tracepoint_iter_reset(iter);
}
#endif /* CONFIG_MODULES */
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)
{
#ifdef CONFIG_MODULES
iter->module = NULL;
#endif /* CONFIG_MODULES */
iter->tracepoint = NULL;
}
EXPORT_SYMBOL_GPL(tracepoint_iter_reset);
#ifdef CONFIG_MODULES
static int tracepoint_module_coming(struct module *mod)
{
struct tp_module *tp_mod, *iter;
int ret = 0;
/*
* We skip modules that tain the kernel, especially those with different
* module header (for forced load), to make sure we don't cause a crash.
*/
if (mod->taints)
return 0;
mutex_lock(&tracepoints_mutex);
tp_mod = kmalloc(sizeof(struct tp_module), GFP_KERNEL);
if (!tp_mod) {
ret = -ENOMEM;
goto end;
}
tp_mod->num_tracepoints = mod->num_tracepoints;
tp_mod->tracepoints_ptrs = mod->tracepoints_ptrs;
/*
* tracepoint_module_list is kept sorted by struct module pointer
* address for iteration on tracepoints from a seq_file that can release
* the mutex between calls.
*/
list_for_each_entry_reverse(iter, &tracepoint_module_list, list) {
BUG_ON(iter == tp_mod); /* Should never be in the list twice */
if (iter < tp_mod) {
/* We belong to the location right after iter. */
list_add(&tp_mod->list, &iter->list);
goto module_added;
}
}
/* We belong to the beginning of the list */
list_add(&tp_mod->list, &tracepoint_module_list);
module_added:
tracepoint_update_probe_range(mod->tracepoints_ptrs,
mod->tracepoints_ptrs + mod->num_tracepoints);
end:
mutex_unlock(&tracepoints_mutex);
return ret;
}
static int tracepoint_module_going(struct module *mod)
{
struct tp_module *pos;
mutex_lock(&tracepoints_mutex);
tracepoint_update_probe_range(mod->tracepoints_ptrs,
mod->tracepoints_ptrs + mod->num_tracepoints);
list_for_each_entry(pos, &tracepoint_module_list, list) {
if (pos->tracepoints_ptrs == mod->tracepoints_ptrs) {
list_del(&pos->list);
kfree(pos);
break;
}
}
/*
* In the case of modules that were tainted at "coming", we'll simply
* walk through the list without finding it. We cannot use the "tainted"
* flag on "going", in case a module taints the kernel only after being
* loaded.
*/
mutex_unlock(&tracepoints_mutex);
return 0;
}
int tracepoint_module_notify(struct notifier_block *self,
unsigned long val, void *data)
{
struct module *mod = data;
int ret = 0;
switch (val) {
case MODULE_STATE_COMING:
ret = tracepoint_module_coming(mod);
break;
case MODULE_STATE_LIVE:
break;
case MODULE_STATE_GOING:
ret = tracepoint_module_going(mod);
break;
}
return ret;
}
struct notifier_block tracepoint_module_nb = {
.notifier_call = tracepoint_module_notify,
.priority = 0,
};
static int init_tracepoints(void)
{
return register_module_notifier(&tracepoint_module_nb);
}
__initcall(init_tracepoints);
#endif /* CONFIG_MODULES */
#ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
/* NB: reg/unreg are called while guarded with the tracepoints_mutex */
static int sys_tracepoint_refcount;
void syscall_regfunc(void)
{
unsigned long flags;
struct task_struct *g, *t;
if (!sys_tracepoint_refcount) {
read_lock_irqsave(&tasklist_lock, flags);
do_each_thread(g, t) {
/* Skip kernel threads. */
if (t->mm)
set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
} while_each_thread(g, t);
read_unlock_irqrestore(&tasklist_lock, flags);
}
sys_tracepoint_refcount++;
}
void syscall_unregfunc(void)
{
unsigned long flags;
struct task_struct *g, *t;
sys_tracepoint_refcount--;
if (!sys_tracepoint_refcount) {
read_lock_irqsave(&tasklist_lock, flags);
do_each_thread(g, t) {
clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
} while_each_thread(g, t);
read_unlock_irqrestore(&tasklist_lock, flags);
}
}
#endif