summaryrefslogtreecommitdiffstats
path: root/kernel/tracepoint.c
diff options
context:
space:
mode:
Diffstat (limited to 'kernel/tracepoint.c')
-rw-r--r--kernel/tracepoint.c477
1 files changed, 477 insertions, 0 deletions
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
new file mode 100644
index 0000000..f2b7c28
--- /dev/null
+++ b/kernel/tracepoint.c
@@ -0,0 +1,477 @@
+/*
+ * 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();
+ call_rcu_sched(&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 & (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;
+ 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 & (TRACEPOINT_TABLE_SIZE - 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_sched has been executed */
+ if (e->rcu_pending)
+ rcu_barrier_sched();
+ 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_sched is pending for this tracepoint,
+ * make sure it's executed now.
+ */
+ if (entry->rcu_pending)
+ rcu_barrier_sched();
+ 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);
+ if (entry->rcu_pending)
+ rcu_barrier_sched();
+ 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_sched();
+ 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;
+ if (entry->rcu_pending)
+ rcu_barrier_sched();
+ 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);
OpenPOWER on IntegriCloud