linux/kernel/marker.c
Mathieu Desnoyers 314de8a9e1 Linux Kernel Markers: fix marker mutex not taken upon module load
Upon module load, we must take the markers mutex.  It implies that the marker
mutex must be nested inside the module mutex.

It implies changing the nesting order : now the marker mutex nests inside the
module mutex.  Make the necessary changes to reverse the order in which the
mutexes are taken.

Includes some cleanup from Dave Hansen <haveblue@us.ibm.com>.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-11-14 18:45:40 -08:00

518 lines
13 KiB
C

/*
* Copyright (C) 2007 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/marker.h>
#include <linux/err.h>
extern struct marker __start___markers[];
extern struct marker __stop___markers[];
/*
* markers_mutex nests inside module_mutex. Markers mutex protects the builtin
* and module markers, the hash table and deferred_sync.
*/
static DEFINE_MUTEX(markers_mutex);
/*
* Marker deferred synchronization.
* Upon marker probe_unregister, we delay call to synchronize_sched() to
* accelerate mass unregistration (only when there is no more reference to a
* given module do we call synchronize_sched()). However, we need to make sure
* every critical region has ended before we re-arm a marker that has been
* unregistered and then registered back with a different probe data.
*/
static int deferred_sync;
/*
* Marker hash table, containing the active markers.
* Protected by module_mutex.
*/
#define MARKER_HASH_BITS 6
#define MARKER_TABLE_SIZE (1 << MARKER_HASH_BITS)
struct marker_entry {
struct hlist_node hlist;
char *format;
marker_probe_func *probe;
void *private;
int refcount; /* Number of times armed. 0 if disarmed. */
char name[0]; /* Contains name'\0'format'\0' */
};
static struct hlist_head marker_table[MARKER_TABLE_SIZE];
/**
* __mark_empty_function - Empty probe callback
* @mdata: pointer of type const struct marker
* @fmt: format string
* @...: variable argument list
*
* Empty callback provided as a probe to the markers. By providing this to a
* disabled marker, we make sure the execution flow is always valid even
* though the function pointer change and the marker enabling are two distinct
* operations that modifies the execution flow of preemptible code.
*/
void __mark_empty_function(const struct marker *mdata, void *private,
const char *fmt, ...)
{
}
EXPORT_SYMBOL_GPL(__mark_empty_function);
/*
* Get marker if the marker is present in the marker hash table.
* Must be called with markers_mutex held.
* Returns NULL if not present.
*/
static struct marker_entry *get_marker(const char *name)
{
struct hlist_head *head;
struct hlist_node *node;
struct marker_entry *e;
u32 hash = jhash(name, strlen(name), 0);
head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
hlist_for_each_entry(e, node, head, hlist) {
if (!strcmp(name, e->name))
return e;
}
return NULL;
}
/*
* Add the marker to the marker hash table. Must be called with markers_mutex
* held.
*/
static int add_marker(const char *name, const char *format,
marker_probe_func *probe, void *private)
{
struct hlist_head *head;
struct hlist_node *node;
struct marker_entry *e;
size_t name_len = strlen(name) + 1;
size_t format_len = 0;
u32 hash = jhash(name, name_len-1, 0);
if (format)
format_len = strlen(format) + 1;
head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
hlist_for_each_entry(e, node, head, hlist) {
if (!strcmp(name, e->name)) {
printk(KERN_NOTICE
"Marker %s busy, probe %p already installed\n",
name, e->probe);
return -EBUSY; /* Already there */
}
}
/*
* Using kmalloc here to allocate a variable length element. Could
* cause some memory fragmentation if overused.
*/
e = kmalloc(sizeof(struct marker_entry) + name_len + format_len,
GFP_KERNEL);
if (!e)
return -ENOMEM;
memcpy(&e->name[0], name, name_len);
if (format) {
e->format = &e->name[name_len];
memcpy(e->format, format, format_len);
trace_mark(core_marker_format, "name %s format %s",
e->name, e->format);
} else
e->format = NULL;
e->probe = probe;
e->private = private;
e->refcount = 0;
hlist_add_head(&e->hlist, head);
return 0;
}
/*
* Remove the marker from the marker hash table. Must be called with mutex_lock
* held.
*/
static void *remove_marker(const char *name)
{
struct hlist_head *head;
struct hlist_node *node;
struct marker_entry *e;
int found = 0;
size_t len = strlen(name) + 1;
void *private = NULL;
u32 hash = jhash(name, len-1, 0);
head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
hlist_for_each_entry(e, node, head, hlist) {
if (!strcmp(name, e->name)) {
found = 1;
break;
}
}
if (found) {
private = e->private;
hlist_del(&e->hlist);
kfree(e);
}
return private;
}
/*
* Set the mark_entry format to the format found in the element.
*/
static int marker_set_format(struct marker_entry **entry, const char *format)
{
struct marker_entry *e;
size_t name_len = strlen((*entry)->name) + 1;
size_t format_len = strlen(format) + 1;
e = kmalloc(sizeof(struct marker_entry) + name_len + format_len,
GFP_KERNEL);
if (!e)
return -ENOMEM;
memcpy(&e->name[0], (*entry)->name, name_len);
e->format = &e->name[name_len];
memcpy(e->format, format, format_len);
e->probe = (*entry)->probe;
e->private = (*entry)->private;
e->refcount = (*entry)->refcount;
hlist_add_before(&e->hlist, &(*entry)->hlist);
hlist_del(&(*entry)->hlist);
kfree(*entry);
*entry = e;
trace_mark(core_marker_format, "name %s format %s",
e->name, e->format);
return 0;
}
/*
* Sets the probe callback corresponding to one marker.
*/
static int set_marker(struct marker_entry **entry, struct marker *elem)
{
int ret;
WARN_ON(strcmp((*entry)->name, elem->name) != 0);
if ((*entry)->format) {
if (strcmp((*entry)->format, elem->format) != 0) {
printk(KERN_NOTICE
"Format mismatch for probe %s "
"(%s), marker (%s)\n",
(*entry)->name,
(*entry)->format,
elem->format);
return -EPERM;
}
} else {
ret = marker_set_format(entry, elem->format);
if (ret)
return ret;
}
elem->call = (*entry)->probe;
elem->private = (*entry)->private;
elem->state = 1;
return 0;
}
/*
* Disable a marker and its probe callback.
* Note: only after a synchronize_sched() issued after setting elem->call to the
* empty function insures that the original callback is not used anymore. This
* insured by preemption disabling around the call site.
*/
static void disable_marker(struct marker *elem)
{
elem->state = 0;
elem->call = __mark_empty_function;
/*
* Leave the private data and id there, because removal is racy and
* should be done only after a synchronize_sched(). These are never used
* until the next initialization anyway.
*/
}
/**
* marker_update_probe_range - Update a probe range
* @begin: beginning of the range
* @end: end of the range
* @probe_module: module address of the probe being updated
* @refcount: number of references left to the given probe_module (out)
*
* Updates the probe callback corresponding to a range of markers.
*/
void marker_update_probe_range(struct marker *begin,
struct marker *end, struct module *probe_module,
int *refcount)
{
struct marker *iter;
struct marker_entry *mark_entry;
mutex_lock(&markers_mutex);
for (iter = begin; iter < end; iter++) {
mark_entry = get_marker(iter->name);
if (mark_entry && mark_entry->refcount) {
set_marker(&mark_entry, iter);
/*
* ignore error, continue
*/
if (probe_module)
if (probe_module ==
__module_text_address((unsigned long)mark_entry->probe))
(*refcount)++;
} else {
disable_marker(iter);
}
}
mutex_unlock(&markers_mutex);
}
/*
* Update probes, removing the faulty probes.
* Issues a synchronize_sched() when no reference to the module passed
* as parameter is found in the probes so the probe module can be
* safely unloaded from now on.
*/
static void marker_update_probes(struct module *probe_module)
{
int refcount = 0;
/* Core kernel markers */
marker_update_probe_range(__start___markers,
__stop___markers, probe_module, &refcount);
/* Markers in modules. */
module_update_markers(probe_module, &refcount);
if (probe_module && refcount == 0) {
synchronize_sched();
deferred_sync = 0;
}
}
/**
* marker_probe_register - Connect a probe to a marker
* @name: marker name
* @format: format string
* @probe: probe handler
* @private: probe private data
*
* private data must be a valid allocated memory address, or NULL.
* Returns 0 if ok, error value on error.
*/
int marker_probe_register(const char *name, const char *format,
marker_probe_func *probe, void *private)
{
struct marker_entry *entry;
int ret = 0;
mutex_lock(&markers_mutex);
entry = get_marker(name);
if (entry && entry->refcount) {
ret = -EBUSY;
goto end;
}
if (deferred_sync) {
synchronize_sched();
deferred_sync = 0;
}
ret = add_marker(name, format, probe, private);
if (ret)
goto end;
mutex_unlock(&markers_mutex);
marker_update_probes(NULL);
return ret;
end:
mutex_unlock(&markers_mutex);
return ret;
}
EXPORT_SYMBOL_GPL(marker_probe_register);
/**
* marker_probe_unregister - Disconnect a probe from a marker
* @name: marker name
*
* Returns the private data given to marker_probe_register, or an ERR_PTR().
*/
void *marker_probe_unregister(const char *name)
{
struct module *probe_module;
struct marker_entry *entry;
void *private;
mutex_lock(&markers_mutex);
entry = get_marker(name);
if (!entry) {
private = ERR_PTR(-ENOENT);
goto end;
}
entry->refcount = 0;
/* In what module is the probe handler ? */
probe_module = __module_text_address((unsigned long)entry->probe);
private = remove_marker(name);
deferred_sync = 1;
mutex_unlock(&markers_mutex);
marker_update_probes(probe_module);
return private;
end:
mutex_unlock(&markers_mutex);
return private;
}
EXPORT_SYMBOL_GPL(marker_probe_unregister);
/**
* marker_probe_unregister_private_data - Disconnect a probe from a marker
* @private: probe private data
*
* Unregister a marker by providing the registered private data.
* Returns the private data given to marker_probe_register, or an ERR_PTR().
*/
void *marker_probe_unregister_private_data(void *private)
{
struct module *probe_module;
struct hlist_head *head;
struct hlist_node *node;
struct marker_entry *entry;
int found = 0;
unsigned int i;
mutex_lock(&markers_mutex);
for (i = 0; i < MARKER_TABLE_SIZE; i++) {
head = &marker_table[i];
hlist_for_each_entry(entry, node, head, hlist) {
if (entry->private == private) {
found = 1;
goto iter_end;
}
}
}
iter_end:
if (!found) {
private = ERR_PTR(-ENOENT);
goto end;
}
entry->refcount = 0;
/* In what module is the probe handler ? */
probe_module = __module_text_address((unsigned long)entry->probe);
private = remove_marker(entry->name);
deferred_sync = 1;
mutex_unlock(&markers_mutex);
marker_update_probes(probe_module);
return private;
end:
mutex_unlock(&markers_mutex);
return private;
}
EXPORT_SYMBOL_GPL(marker_probe_unregister_private_data);
/**
* marker_arm - Arm a marker
* @name: marker name
*
* Activate a marker. It keeps a reference count of the number of
* arming/disarming done.
* Returns 0 if ok, error value on error.
*/
int marker_arm(const char *name)
{
struct marker_entry *entry;
int ret = 0;
mutex_lock(&markers_mutex);
entry = get_marker(name);
if (!entry) {
ret = -ENOENT;
goto end;
}
/*
* Only need to update probes when refcount passes from 0 to 1.
*/
if (entry->refcount++)
goto end;
end:
mutex_unlock(&markers_mutex);
marker_update_probes(NULL);
return ret;
}
EXPORT_SYMBOL_GPL(marker_arm);
/**
* marker_disarm - Disarm a marker
* @name: marker name
*
* Disarm a marker. It keeps a reference count of the number of arming/disarming
* done.
* Returns 0 if ok, error value on error.
*/
int marker_disarm(const char *name)
{
struct marker_entry *entry;
int ret = 0;
mutex_lock(&markers_mutex);
entry = get_marker(name);
if (!entry) {
ret = -ENOENT;
goto end;
}
/*
* Only permit decrement refcount if higher than 0.
* Do probe update only on 1 -> 0 transition.
*/
if (entry->refcount) {
if (--entry->refcount)
goto end;
} else {
ret = -EPERM;
goto end;
}
end:
mutex_unlock(&markers_mutex);
marker_update_probes(NULL);
return ret;
}
EXPORT_SYMBOL_GPL(marker_disarm);
/**
* marker_get_private_data - Get a marker's probe private data
* @name: marker name
*
* Returns the private data pointer, or an ERR_PTR.
* The private data pointer should _only_ be dereferenced if the caller is the
* owner of the data, or its content could vanish. This is mostly used to
* confirm that a caller is the owner of a registered probe.
*/
void *marker_get_private_data(const char *name)
{
struct hlist_head *head;
struct hlist_node *node;
struct marker_entry *e;
size_t name_len = strlen(name) + 1;
u32 hash = jhash(name, name_len-1, 0);
int found = 0;
head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
hlist_for_each_entry(e, node, head, hlist) {
if (!strcmp(name, e->name)) {
found = 1;
return e->private;
}
}
return ERR_PTR(-ENOENT);
}
EXPORT_SYMBOL_GPL(marker_get_private_data);