signals: annotate lock context change on ptrace_stop()

[mirror_ubuntu-artful-kernel.git] / kernel / tracepoint.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 __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)
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 && !elem->state && active)
                elem->regfunc();
        else if (elem->unregfunc && elem->state && !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 (!elem->state && active) {
                jump_label_enable(&elem->state);
                elem->state = active;
        } else if (elem->state && !active) {
                jump_label_disable(&elem->state);
                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)
{
        if (elem->unregfunc && elem->state)
                elem->unregfunc();

        if (elem->state) {
                jump_label_disable(&elem->state);
                elem->state = 0;
        }
        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.
 */
void
tracepoint_update_probe_range(struct tracepoint *begin, struct tracepoint *end)
{
        struct tracepoint *iter;
        struct tracepoint_entry *mark_entry;

        if (!begin)
                return;

        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();
}

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);
        mutex_unlock(&tracepoints_mutex);
        if (IS_ERR(old))
                return PTR_ERR(old);

        tracepoint_update_probes();             /* may update entry */
        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);
        mutex_unlock(&tracepoints_mutex);
        if (IS_ERR(old))
                return PTR_ERR(old);

        tracepoint_update_probes();             /* may update entry */
        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;
        mutex_unlock(&tracepoints_mutex);

        tracepoint_update_probes();
        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.
 */
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);

#ifdef CONFIG_MODULES

int tracepoint_module_notify(struct notifier_block *self,
                             unsigned long val, void *data)
{
        struct module *mod = data;

        switch (val) {
        case MODULE_STATE_COMING:
        case MODULE_STATE_GOING:
                tracepoint_update_probe_range(mod->tracepoints,
                        mod->tracepoints + mod->num_tracepoints);
                break;
        }
        return 0;
}

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