tracepoint.c

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/*
 * 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/static_key.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 && !static_key_enabled(&elem->key) && active)
        elem->regfunc();
    else if (elem->unregfunc && static_key_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 && !static_key_enabled(&elem->key))
        static_key_slow_inc(&elem->key);
    else if (!active && static_key_enabled(&elem->key))
        static_key_slow_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 && static_key_enabled(&elem->key))
        elem->unregfunc();

    if (static_key_enabled(&elem->key))
        static_key_slow_dec(&elem->key);
    rcu_assign_pointer(elem->funcs, NULL);
}

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;
}

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;
}

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);
    }
}

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);

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);

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);

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 taint the kernel, especially those with different
     * module headers (for forced load), to make sure we don't cause a crash.
     * Staging and out-of-tree GPL modules are fine.
     */
    if (mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP)))
        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