ftrace: add README

[deliverable/linux.git] / kernel / trace / trace.c

/*
 * ring buffer based function tracer
 *
 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
 * Copyright (C) 2008 Ingo Molnar <mingo@redhat.com>
 *
 * Originally taken from the RT patch by:
 *    Arnaldo Carvalho de Melo <acme@redhat.com>
 *
 * Based on code from the latency_tracer, that is:
 *  Copyright (C) 2004-2006 Ingo Molnar
 *  Copyright (C) 2004 William Lee Irwin III
 */
#include <linux/utsrelease.h>
#include <linux/kallsyms.h>
#include <linux/seq_file.h>
#include <linux/debugfs.h>
#include <linux/pagemap.h>
#include <linux/hardirq.h>
#include <linux/linkage.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/ctype.h>
#include <linux/init.h>
#include <linux/gfp.h>
#include <linux/fs.h>

#include "trace.h"

unsigned long __read_mostly     tracing_max_latency = (cycle_t)ULONG_MAX;
unsigned long __read_mostly     tracing_thresh;

static int tracing_disabled = 1;

static long notrace
ns2usecs(cycle_t nsec)
{
        nsec += 500;
        do_div(nsec, 1000);
        return nsec;
}

static atomic_t                 tracer_counter;
static struct trace_array       global_trace;

static DEFINE_PER_CPU(struct trace_array_cpu, global_trace_cpu);

static struct trace_array       max_tr;

static DEFINE_PER_CPU(struct trace_array_cpu, max_data);

static int                      tracer_enabled;
static unsigned long            trace_nr_entries = 16384UL;

static struct tracer            *trace_types __read_mostly;
static struct tracer            *current_trace __read_mostly;
static int                      max_tracer_type_len;

static DEFINE_MUTEX(trace_types_lock);

#define ENTRIES_PER_PAGE (PAGE_SIZE / sizeof(struct trace_entry))

static int __init set_nr_entries(char *str)
{
        if (!str)
                return 0;
        trace_nr_entries = simple_strtoul(str, &str, 0);
        return 1;
}
__setup("trace_entries=", set_nr_entries);

unsigned long nsecs_to_usecs(unsigned long nsecs)
{
        return nsecs / 1000;
}

enum trace_type {
        __TRACE_FIRST_TYPE = 0,

        TRACE_FN,
        TRACE_CTX,

        __TRACE_LAST_TYPE
};

enum trace_flag_type {
        TRACE_FLAG_IRQS_OFF             = 0x01,
        TRACE_FLAG_NEED_RESCHED         = 0x02,
        TRACE_FLAG_HARDIRQ              = 0x04,
        TRACE_FLAG_SOFTIRQ              = 0x08,
};

enum trace_iterator_flags {
        TRACE_ITER_PRINT_PARENT         = 0x01,
        TRACE_ITER_SYM_OFFSET           = 0x02,
        TRACE_ITER_SYM_ADDR             = 0x04,
        TRACE_ITER_VERBOSE              = 0x08,
};

#define TRACE_ITER_SYM_MASK \
        (TRACE_ITER_PRINT_PARENT|TRACE_ITER_SYM_OFFSET|TRACE_ITER_SYM_ADDR)

/* These must match the bit postions above */
static const char *trace_options[] = {
        "print-parent",
        "sym-offset",
        "sym-addr",
        "verbose",
        NULL
};

static unsigned trace_flags;

static DEFINE_SPINLOCK(ftrace_max_lock);

/*
 * Copy the new maximum trace into the separate maximum-trace
 * structure. (this way the maximum trace is permanently saved,
 * for later retrieval via /debugfs/tracing/latency_trace)
 */
static void notrace
__update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
{
        struct trace_array_cpu *data = tr->data[cpu];

        max_tr.cpu = cpu;
        max_tr.time_start = data->preempt_timestamp;

        data = max_tr.data[cpu];
        data->saved_latency = tracing_max_latency;

        memcpy(data->comm, tsk->comm, TASK_COMM_LEN);
        data->pid = tsk->pid;
        data->uid = tsk->uid;
        data->nice = tsk->static_prio - 20 - MAX_RT_PRIO;
        data->policy = tsk->policy;
        data->rt_priority = tsk->rt_priority;

        /* record this tasks comm */
        tracing_record_cmdline(current);
}

void check_pages(struct trace_array_cpu *data)
{
        struct page *page, *tmp;

        BUG_ON(data->trace_pages.next->prev != &data->trace_pages);
        BUG_ON(data->trace_pages.prev->next != &data->trace_pages);

        list_for_each_entry_safe(page, tmp, &data->trace_pages, lru) {
                BUG_ON(page->lru.next->prev != &page->lru);
                BUG_ON(page->lru.prev->next != &page->lru);
        }
}

void *head_page(struct trace_array_cpu *data)
{
        struct page *page;

        check_pages(data);
        if (list_empty(&data->trace_pages))
                return NULL;

        page = list_entry(data->trace_pages.next, struct page, lru);
        BUG_ON(&page->lru == &data->trace_pages);

        return page_address(page);
}

notrace static void
flip_trace(struct trace_array_cpu *tr1, struct trace_array_cpu *tr2)
{
        struct list_head flip_pages;

        INIT_LIST_HEAD(&flip_pages);

        tr1->trace_current = NULL;
        memcpy(&tr1->trace_current_idx, &tr2->trace_current_idx,
                sizeof(struct trace_array_cpu) -
                offsetof(struct trace_array_cpu, trace_current_idx));

        check_pages(tr1);
        check_pages(tr2);
        list_splice_init(&tr1->trace_pages, &flip_pages);
        list_splice_init(&tr2->trace_pages, &tr1->trace_pages);
        list_splice_init(&flip_pages, &tr2->trace_pages);
        BUG_ON(!list_empty(&flip_pages));
        check_pages(tr1);
        check_pages(tr2);
}

notrace void
update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
{
        struct trace_array_cpu *data;
        int i;

        WARN_ON_ONCE(!irqs_disabled());
        spin_lock(&ftrace_max_lock);
        /* clear out all the previous traces */
        for_each_possible_cpu(i) {
                data = tr->data[i];
                flip_trace(max_tr.data[i], data);
                tracing_reset(data);
        }

        __update_max_tr(tr, tsk, cpu);
        spin_unlock(&ftrace_max_lock);
}

/**
 * update_max_tr_single - only copy one trace over, and reset the rest
 * @tr - tracer
 * @tsk - task with the latency
 * @cpu - the cpu of the buffer to copy.
 */
notrace void
update_max_tr_single(struct trace_array *tr, struct task_struct *tsk, int cpu)
{
        struct trace_array_cpu *data = tr->data[cpu];
        int i;

        WARN_ON_ONCE(!irqs_disabled());
        spin_lock(&ftrace_max_lock);
        for_each_possible_cpu(i)
                tracing_reset(max_tr.data[i]);

        flip_trace(max_tr.data[cpu], data);

        tracing_reset(data);

        __update_max_tr(tr, tsk, cpu);
        spin_unlock(&ftrace_max_lock);
}

int register_tracer(struct tracer *type)
{
        struct tracer *t;
        int len;
        int ret = 0;

        if (!type->name) {
                pr_info("Tracer must have a name\n");
                return -1;
        }

        mutex_lock(&trace_types_lock);
        for (t = trace_types; t; t = t->next) {
                if (strcmp(type->name, t->name) == 0) {
                        /* already found */
                        pr_info("Trace %s already registered\n",
                                type->name);
                        ret = -1;
                        goto out;
                }
        }

#ifdef CONFIG_FTRACE_STARTUP_TEST
        if (type->selftest) {
                struct tracer *saved_tracer = current_trace;
                struct trace_array_cpu *data;
                struct trace_array *tr = &global_trace;
                int saved_ctrl = tr->ctrl;
                int i;
                /*
                 * Run a selftest on this tracer.
                 * Here we reset the trace buffer, and set the current
                 * tracer to be this tracer. The tracer can then run some
                 * internal tracing to verify that everything is in order.
                 * If we fail, we do not register this tracer.
                 */
                for_each_possible_cpu(i) {
                        data = tr->data[i];
                        if (!head_page(data))
                                continue;
                        tracing_reset(data);
                }
                current_trace = type;
                tr->ctrl = 0;
                /* the test is responsible for initializing and enabling */
                pr_info("Testing tracer %s: ", type->name);
                ret = type->selftest(type, tr);
                /* the test is responsible for resetting too */
                current_trace = saved_tracer;
                tr->ctrl = saved_ctrl;
                if (ret) {
                        printk(KERN_CONT "FAILED!\n");
                        goto out;
                }
                printk(KERN_CONT "PASSED\n");
        }
#endif

        type->next = trace_types;
        trace_types = type;
        len = strlen(type->name);
        if (len > max_tracer_type_len)
                max_tracer_type_len = len;

 out:
        mutex_unlock(&trace_types_lock);

        return ret;
}

void unregister_tracer(struct tracer *type)
{
        struct tracer **t;
        int len;

        mutex_lock(&trace_types_lock);
        for (t = &trace_types; *t; t = &(*t)->next) {
                if (*t == type)
                        goto found;
        }
        pr_info("Trace %s not registered\n", type->name);
        goto out;

 found:
        *t = (*t)->next;
        if (strlen(type->name) != max_tracer_type_len)
                goto out;

        max_tracer_type_len = 0;
        for (t = &trace_types; *t; t = &(*t)->next) {
                len = strlen((*t)->name);
                if (len > max_tracer_type_len)
                        max_tracer_type_len = len;
        }
 out:
        mutex_unlock(&trace_types_lock);
}

void notrace tracing_reset(struct trace_array_cpu *data)
{
        data->trace_idx = 0;
        data->trace_current = head_page(data);
        data->trace_current_idx = 0;
}

#ifdef CONFIG_FTRACE
static void notrace
function_trace_call(unsigned long ip, unsigned long parent_ip)
{
        struct trace_array *tr = &global_trace;
        struct trace_array_cpu *data;
        unsigned long flags;
        long disabled;
        int cpu;

        if (unlikely(!tracer_enabled))
                return;

        local_irq_save(flags);
        cpu = raw_smp_processor_id();
        data = tr->data[cpu];
        disabled = atomic_inc_return(&data->disabled);

        if (likely(disabled == 1))
                ftrace(tr, data, ip, parent_ip, flags);

        atomic_dec(&data->disabled);
        local_irq_restore(flags);
}

static struct ftrace_ops trace_ops __read_mostly =
{
        .func = function_trace_call,
};
#endif

notrace void tracing_start_function_trace(void)
{
        register_ftrace_function(&trace_ops);
}

notrace void tracing_stop_function_trace(void)
{
        unregister_ftrace_function(&trace_ops);
}

#define SAVED_CMDLINES 128
static unsigned map_pid_to_cmdline[PID_MAX_DEFAULT+1];
static unsigned map_cmdline_to_pid[SAVED_CMDLINES];
static char saved_cmdlines[SAVED_CMDLINES][TASK_COMM_LEN];
static int cmdline_idx;
static DEFINE_SPINLOCK(trace_cmdline_lock);
atomic_t trace_record_cmdline_disabled;

static void trace_init_cmdlines(void)
{
        memset(&map_pid_to_cmdline, -1, sizeof(map_pid_to_cmdline));
        memset(&map_cmdline_to_pid, -1, sizeof(map_cmdline_to_pid));
        cmdline_idx = 0;
}

notrace void trace_stop_cmdline_recording(void);

static void notrace trace_save_cmdline(struct task_struct *tsk)
{
        unsigned map;
        unsigned idx;

        if (!tsk->pid || unlikely(tsk->pid > PID_MAX_DEFAULT))
                return;

        /*
         * It's not the end of the world if we don't get
         * the lock, but we also don't want to spin
         * nor do we want to disable interrupts,
         * so if we miss here, then better luck next time.
         */
        if (!spin_trylock(&trace_cmdline_lock))
                return;

        idx = map_pid_to_cmdline[tsk->pid];
        if (idx >= SAVED_CMDLINES) {
                idx = (cmdline_idx + 1) % SAVED_CMDLINES;

                map = map_cmdline_to_pid[idx];
                if (map <= PID_MAX_DEFAULT)
                        map_pid_to_cmdline[map] = (unsigned)-1;

                map_pid_to_cmdline[tsk->pid] = idx;

                cmdline_idx = idx;
        }

        memcpy(&saved_cmdlines[idx], tsk->comm, TASK_COMM_LEN);

        spin_unlock(&trace_cmdline_lock);
}

static notrace char *trace_find_cmdline(int pid)
{
        char *cmdline = "<...>";
        unsigned map;

        if (!pid)
                return "<idle>";

        if (pid > PID_MAX_DEFAULT)
                goto out;

        map = map_pid_to_cmdline[pid];
        if (map >= SAVED_CMDLINES)
                goto out;

        cmdline = saved_cmdlines[map];

 out:
        return cmdline;
}

notrace void tracing_record_cmdline(struct task_struct *tsk)
{
        if (atomic_read(&trace_record_cmdline_disabled))
                return;

        trace_save_cmdline(tsk);
}

static inline notrace struct trace_entry *
tracing_get_trace_entry(struct trace_array *tr, struct trace_array_cpu *data)
{
        unsigned long idx, idx_next;
        struct trace_entry *entry;
        struct list_head *next;
        struct page *page;

        data->trace_idx++;
        idx = data->trace_current_idx;
        idx_next = idx + 1;

        BUG_ON(idx * TRACE_ENTRY_SIZE >= PAGE_SIZE);

        entry = data->trace_current + idx * TRACE_ENTRY_SIZE;

        if (unlikely(idx_next >= ENTRIES_PER_PAGE)) {
                page = virt_to_page(data->trace_current);
                /*
                 * Roundrobin - but skip the head (which is not a real page):
                 */
                next = page->lru.next;
                if (unlikely(next == &data->trace_pages))
                        next = next->next;
                BUG_ON(next == &data->trace_pages);

                page = list_entry(next, struct page, lru);
                data->trace_current = page_address(page);
                idx_next = 0;
        }

        data->trace_current_idx = idx_next;

        return entry;
}

static inline notrace void
tracing_generic_entry_update(struct trace_entry *entry, unsigned long flags)
{
        struct task_struct *tsk = current;
        unsigned long pc;

        pc = preempt_count();

        entry->idx              = atomic_inc_return(&tracer_counter);
        entry->preempt_count    = pc & 0xff;
        entry->pid              = tsk->pid;
        entry->t                = now(raw_smp_processor_id());
        entry->flags = (irqs_disabled_flags(flags) ? TRACE_FLAG_IRQS_OFF : 0) |
                ((pc & HARDIRQ_MASK) ? TRACE_FLAG_HARDIRQ : 0) |
                ((pc & SOFTIRQ_MASK) ? TRACE_FLAG_SOFTIRQ : 0) |
                (need_resched() ? TRACE_FLAG_NEED_RESCHED : 0);
}

notrace void
ftrace(struct trace_array *tr, struct trace_array_cpu *data,
       unsigned long ip, unsigned long parent_ip, unsigned long flags)
{
        struct trace_entry *entry;

        entry                   = tracing_get_trace_entry(tr, data);
        tracing_generic_entry_update(entry, flags);
        entry->type             = TRACE_FN;
        entry->fn.ip            = ip;
        entry->fn.parent_ip     = parent_ip;
}

notrace void
tracing_sched_switch_trace(struct trace_array *tr,
                           struct trace_array_cpu *data,
                           struct task_struct *prev, struct task_struct *next,
                           unsigned long flags)
{
        struct trace_entry *entry;

        entry                   = tracing_get_trace_entry(tr, data);
        tracing_generic_entry_update(entry, flags);
        entry->type             = TRACE_CTX;
        entry->ctx.prev_pid     = prev->pid;
        entry->ctx.prev_prio    = prev->prio;
        entry->ctx.prev_state   = prev->state;
        entry->ctx.next_pid     = next->pid;
        entry->ctx.next_prio    = next->prio;
}

enum trace_file_type {
        TRACE_FILE_LAT_FMT      = 1,
};

static struct trace_entry *
trace_entry_idx(struct trace_array *tr, struct trace_array_cpu *data,
                struct trace_iterator *iter, int cpu)
{
        struct page *page;
        struct trace_entry *array;

        if (iter->next_idx[cpu] >= tr->entries ||
            iter->next_idx[cpu] >= data->trace_idx)
                return NULL;

        if (!iter->next_page[cpu]) {
                /*
                 * Initialize. If the count of elements in
                 * this buffer is greater than the max entries
                 * we had an underrun. Which means we looped around.
                 * We can simply use the current pointer as our
                 * starting point.
                 */
                if (data->trace_idx >= tr->entries) {
                        page = virt_to_page(data->trace_current);
                        iter->next_page[cpu] = &page->lru;
                        iter->next_page_idx[cpu] = data->trace_current_idx;
                } else {
                        iter->next_page[cpu] = data->trace_pages.next;
                        iter->next_page_idx[cpu] = 0;
                }
        }

        page = list_entry(iter->next_page[cpu], struct page, lru);
        BUG_ON(&data->trace_pages == &page->lru);

        array = page_address(page);

        return &array[iter->next_page_idx[cpu]];
}

static struct notrace trace_entry *
find_next_entry(struct trace_iterator *iter, int *ent_cpu)
{
        struct trace_array *tr = iter->tr;
        struct trace_entry *ent, *next = NULL;
        int next_cpu = -1;
        int cpu;

        for_each_possible_cpu(cpu) {
                if (!head_page(tr->data[cpu]))
                        continue;
                ent = trace_entry_idx(tr, tr->data[cpu], iter, cpu);
                if (ent &&
                    (!next || (long)(next->idx - ent->idx) > 0)) {
                        next = ent;
                        next_cpu = cpu;
                }
        }

        if (ent_cpu)
                *ent_cpu = next_cpu;

        return next;
}

static void *find_next_entry_inc(struct trace_iterator *iter)
{
        struct trace_entry *next;
        int next_cpu = -1;

        next = find_next_entry(iter, &next_cpu);

        if (next) {
                iter->idx++;
                iter->next_idx[next_cpu]++;
                iter->next_page_idx[next_cpu]++;
                if (iter->next_page_idx[next_cpu] >= ENTRIES_PER_PAGE) {
                        struct trace_array_cpu *data = iter->tr->data[next_cpu];

                        iter->next_page_idx[next_cpu] = 0;
                        iter->next_page[next_cpu] =
                                iter->next_page[next_cpu]->next;
                        if (iter->next_page[next_cpu] == &data->trace_pages)
                                iter->next_page[next_cpu] =
                                        data->trace_pages.next;
                }
        }
        iter->ent = next;
        iter->cpu = next_cpu;

        return next ? iter : NULL;
}

static void notrace *
s_next(struct seq_file *m, void *v, loff_t *pos)
{
        struct trace_iterator *iter = m->private;
        void *ent;
        void *last_ent = iter->ent;
        int i = (int)*pos;

        (*pos)++;

        /* can't go backwards */
        if (iter->idx > i)
                return NULL;

        if (iter->idx < 0)
                ent = find_next_entry_inc(iter);
        else
                ent = iter;

        while (ent && iter->idx < i)
                ent = find_next_entry_inc(iter);

        iter->pos = *pos;

        if (last_ent && !ent)
                seq_puts(m, "\n\nvim:ft=help\n");

        return ent;
}

static void *s_start(struct seq_file *m, loff_t *pos)
{
        struct trace_iterator *iter = m->private;
        void *p = NULL;
        loff_t l = 0;
        int i;

        mutex_lock(&trace_types_lock);

        if (!current_trace || current_trace != iter->trace)
                return NULL;

        atomic_inc(&trace_record_cmdline_disabled);

        /* let the tracer grab locks here if needed */
        if (current_trace->start)
                current_trace->start(iter);

        if (*pos != iter->pos) {
                iter->ent = NULL;
                iter->cpu = 0;
                iter->idx = -1;

                for_each_possible_cpu(i) {
                        iter->next_idx[i] = 0;
                        iter->next_page[i] = NULL;
                }

                for (p = iter; p && l < *pos; p = s_next(m, p, &l))
                        ;

        } else {
                l = *pos - 1;
                p = s_next(m, p, &l);
        }

        return p;
}

static void s_stop(struct seq_file *m, void *p)
{
        struct trace_iterator *iter = m->private;

        atomic_dec(&trace_record_cmdline_disabled);

        /* let the tracer release locks here if needed */
        if (current_trace && current_trace == iter->trace && iter->trace->stop)
                iter->trace->stop(iter);

        mutex_unlock(&trace_types_lock);
}

static void
seq_print_sym_short(struct seq_file *m, const char *fmt, unsigned long address)
{
#ifdef CONFIG_KALLSYMS
        char str[KSYM_SYMBOL_LEN];

        kallsyms_lookup(address, NULL, NULL, NULL, str);

        seq_printf(m, fmt, str);
#endif
}

static void
seq_print_sym_offset(struct seq_file *m, const char *fmt, unsigned long address)
{
#ifdef CONFIG_KALLSYMS
        char str[KSYM_SYMBOL_LEN];

        sprint_symbol(str, address);
        seq_printf(m, fmt, str);
#endif
}

#ifndef CONFIG_64BIT
# define IP_FMT "%08lx"
#else
# define IP_FMT "%016lx"
#endif

static void notrace
seq_print_ip_sym(struct seq_file *m, unsigned long ip, unsigned long sym_flags)
{
        if (!ip) {
                seq_printf(m, "0");
                return;
        }

        if (sym_flags & TRACE_ITER_SYM_OFFSET)
                seq_print_sym_offset(m, "%s", ip);
        else
                seq_print_sym_short(m, "%s", ip);

        if (sym_flags & TRACE_ITER_SYM_ADDR)
                seq_printf(m, " <" IP_FMT ">", ip);
}

static void notrace print_lat_help_header(struct seq_file *m)
{
        seq_puts(m, "#                _------=> CPU#            \n");
        seq_puts(m, "#               / _-----=> irqs-off        \n");
        seq_puts(m, "#              | / _----=> need-resched    \n");
        seq_puts(m, "#              || / _---=> hardirq/softirq \n");
        seq_puts(m, "#              ||| / _--=> preempt-depth   \n");
        seq_puts(m, "#              |||| /                      \n");
        seq_puts(m, "#              |||||     delay             \n");
        seq_puts(m, "#  cmd     pid ||||| time  |   caller      \n");
        seq_puts(m, "#     \\   /    |||||   \\   |   /           \n");
}

static void notrace print_func_help_header(struct seq_file *m)
{
        seq_puts(m, "#           TASK-PID   CPU#    TIMESTAMP  FUNCTION\n");
        seq_puts(m, "#              | |      |          |         |\n");
}


static void notrace
print_trace_header(struct seq_file *m, struct trace_iterator *iter)
{
        unsigned long sym_flags = (trace_flags & TRACE_ITER_SYM_MASK);
        struct trace_array *tr = iter->tr;
        struct trace_array_cpu *data = tr->data[tr->cpu];
        struct tracer *type = current_trace;
        unsigned long total   = 0;
        unsigned long entries = 0;
        int cpu;
        const char *name = "preemption";

        if (type)
                name = type->name;

        for_each_possible_cpu(cpu) {
                if (head_page(tr->data[cpu])) {
                        total += tr->data[cpu]->trace_idx;
                        if (tr->data[cpu]->trace_idx > tr->entries)
                                entries += tr->entries;
                        else
                                entries += tr->data[cpu]->trace_idx;
                }
        }

        seq_printf(m, "%s latency trace v1.1.5 on %s\n",
                   name, UTS_RELEASE);
        seq_puts(m, "-----------------------------------"
                 "---------------------------------\n");
        seq_printf(m, " latency: %lu us, #%lu/%lu, CPU#%d |"
                   " (M:%s VP:%d, KP:%d, SP:%d HP:%d",
                   nsecs_to_usecs(data->saved_latency),
                   entries,
                   total,
                   tr->cpu,
#if defined(CONFIG_PREEMPT_NONE)
                   "server",
#elif defined(CONFIG_PREEMPT_VOLUNTARY)
                   "desktop",
#elif defined(CONFIG_PREEMPT_DESKTOP)
                   "preempt",
#else
                   "unknown",
#endif
                   /* These are reserved for later use */
                   0, 0, 0, 0);
#ifdef CONFIG_SMP
        seq_printf(m, " #P:%d)\n", num_online_cpus());
#else
        seq_puts(m, ")\n");
#endif
        seq_puts(m, "    -----------------\n");
        seq_printf(m, "    | task: %.16s-%d "
                   "(uid:%d nice:%ld policy:%ld rt_prio:%ld)\n",
                   data->comm, data->pid, data->uid, data->nice,
                   data->policy, data->rt_priority);
        seq_puts(m, "    -----------------\n");

        if (data->critical_start) {
                seq_puts(m, " => started at: ");
                seq_print_ip_sym(m, data->critical_start, sym_flags);
                seq_puts(m, "\n => ended at:   ");
                seq_print_ip_sym(m, data->critical_end, sym_flags);
                seq_puts(m, "\n");
        }

        seq_puts(m, "\n");
}

static void notrace
lat_print_generic(struct seq_file *m, struct trace_entry *entry, int cpu)
{
        int hardirq, softirq;
        char *comm;

        comm = trace_find_cmdline(entry->pid);

        seq_printf(m, "%8.8s-%-5d ", comm, entry->pid);
        seq_printf(m, "%d", cpu);
        seq_printf(m, "%c%c",
                   (entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' : '.',
                   ((entry->flags & TRACE_FLAG_NEED_RESCHED) ? 'N' : '.'));

        hardirq = entry->flags & TRACE_FLAG_HARDIRQ;
        softirq = entry->flags & TRACE_FLAG_SOFTIRQ;
        if (hardirq && softirq)
                seq_putc(m, 'H');
        else {
                if (hardirq)
                        seq_putc(m, 'h');
                else {
                        if (softirq)
                                seq_putc(m, 's');
                        else
                                seq_putc(m, '.');
                }
        }

        if (entry->preempt_count)
                seq_printf(m, "%x", entry->preempt_count);
        else
                seq_puts(m, ".");
}

unsigned long preempt_mark_thresh = 100;

static void notrace
lat_print_timestamp(struct seq_file *m, unsigned long long abs_usecs,
                    unsigned long rel_usecs)
{
        seq_printf(m, " %4lldus", abs_usecs);
        if (rel_usecs > preempt_mark_thresh)
                seq_puts(m, "!: ");
        else if (rel_usecs > 1)
                seq_puts(m, "+: ");
        else
                seq_puts(m, " : ");
}

static const char state_to_char[] = TASK_STATE_TO_CHAR_STR;

static void notrace
print_lat_fmt(struct seq_file *m, struct trace_iterator *iter,
              unsigned int trace_idx, int cpu)
{
        unsigned long sym_flags = (trace_flags & TRACE_ITER_SYM_MASK);
        struct trace_entry *next_entry = find_next_entry(iter, NULL);
        unsigned long verbose = (trace_flags & TRACE_ITER_VERBOSE);
        struct trace_entry *entry = iter->ent;
        unsigned long abs_usecs;
        unsigned long rel_usecs;
        char *comm;
        int S;

        if (!next_entry)
                next_entry = entry;
        rel_usecs = ns2usecs(next_entry->t - entry->t);
        abs_usecs = ns2usecs(entry->t - iter->tr->time_start);

        if (verbose) {
                comm = trace_find_cmdline(entry->pid);
                seq_printf(m, "%16s %5d %d %d %08x %08x [%08lx]"
                           " %ld.%03ldms (+%ld.%03ldms): ",
                           comm,
                           entry->pid, cpu, entry->flags,
                           entry->preempt_count, trace_idx,
                           ns2usecs(entry->t),
                           abs_usecs/1000,
                           abs_usecs % 1000, rel_usecs/1000, rel_usecs % 1000);
        } else {
                lat_print_generic(m, entry, cpu);
                lat_print_timestamp(m, abs_usecs, rel_usecs);
        }
        switch (entry->type) {
        case TRACE_FN:
                seq_print_ip_sym(m, entry->fn.ip, sym_flags);
                seq_puts(m, " (");
                seq_print_ip_sym(m, entry->fn.parent_ip, sym_flags);
                seq_puts(m, ")\n");
                break;
        case TRACE_CTX:
                S = entry->ctx.prev_state < sizeof(state_to_char) ?
                        state_to_char[entry->ctx.prev_state] : 'X';
                comm = trace_find_cmdline(entry->ctx.next_pid);
                seq_printf(m, " %d:%d:%c --> %d:%d %s\n",
                           entry->ctx.prev_pid,
                           entry->ctx.prev_prio,
                           S,
                           entry->ctx.next_pid,
                           entry->ctx.next_prio,
                           comm);
                break;
        default:
                seq_printf(m, "Unknown type %d\n", entry->type);
        }
}

static void notrace
print_trace_fmt(struct seq_file *m, struct trace_iterator *iter)
{
        unsigned long sym_flags = (trace_flags & TRACE_ITER_SYM_MASK);
        struct trace_entry *entry = iter->ent;
        unsigned long usec_rem;
        unsigned long long t;
        unsigned long secs;
        char *comm;
        int S;

        comm = trace_find_cmdline(iter->ent->pid);

        t = ns2usecs(entry->t);
        usec_rem = do_div(t, 1000000ULL);
        secs = (unsigned long)t;

        seq_printf(m, "%16s-%-5d ", comm, entry->pid);
        seq_printf(m, "[%02d] ", iter->cpu);
        seq_printf(m, "%5lu.%06lu: ", secs, usec_rem);

        switch (entry->type) {
        case TRACE_FN:
                seq_print_ip_sym(m, entry->fn.ip, sym_flags);
                if ((sym_flags & TRACE_ITER_PRINT_PARENT) &&
                                                entry->fn.parent_ip) {
                        seq_printf(m, " <-");
                        seq_print_ip_sym(m, entry->fn.parent_ip, sym_flags);
                }
                seq_printf(m, "\n");
                break;
        case TRACE_CTX:
                S = entry->ctx.prev_state < sizeof(state_to_char) ?
                        state_to_char[entry->ctx.prev_state] : 'X';
                seq_printf(m, " %d:%d:%c ==> %d:%d\n",
                           entry->ctx.prev_pid,
                           entry->ctx.prev_prio,
                           S,
                           entry->ctx.next_pid,
                           entry->ctx.next_prio);
                break;
        }
}

static int trace_empty(struct trace_iterator *iter)
{
        struct trace_array_cpu *data;
        int cpu;

        for_each_possible_cpu(cpu) {
                data = iter->tr->data[cpu];

                if (head_page(data) && data->trace_idx)
                        return 0;
        }
        return 1;
}

static int s_show(struct seq_file *m, void *v)
{
        struct trace_iterator *iter = v;

        if (iter->ent == NULL) {
                if (iter->tr) {
                        seq_printf(m, "# tracer: %s\n", iter->trace->name);
                        seq_puts(m, "#\n");
                }
                if (iter->iter_flags & TRACE_FILE_LAT_FMT) {
                        /* print nothing if the buffers are empty */
                        if (trace_empty(iter))
                                return 0;
                        print_trace_header(m, iter);
                        if (!(trace_flags & TRACE_ITER_VERBOSE))
                                print_lat_help_header(m);
                } else {
                        if (!(trace_flags & TRACE_ITER_VERBOSE))
                                print_func_help_header(m);
                }
        } else {
                if (iter->iter_flags & TRACE_FILE_LAT_FMT)
                        print_lat_fmt(m, iter, iter->idx, iter->cpu);
                else
                        print_trace_fmt(m, iter);
        }

        return 0;
}

static struct seq_operations tracer_seq_ops = {
        .start = s_start,
        .next = s_next,
        .stop = s_stop,
        .show = s_show,
};

static struct trace_iterator notrace *
__tracing_open(struct inode *inode, struct file *file, int *ret)
{
        struct trace_iterator *iter;

        if (tracing_disabled) {
                *ret = -ENODEV;
                return NULL;
        }

        iter = kzalloc(sizeof(*iter), GFP_KERNEL);
        if (!iter) {
                *ret = -ENOMEM;
                goto out;
        }

        mutex_lock(&trace_types_lock);
        if (current_trace && current_trace->print_max)
                iter->tr = &max_tr;
        else
                iter->tr = inode->i_private;
        iter->trace = current_trace;
        iter->pos = -1;

        /* TODO stop tracer */
        *ret = seq_open(file, &tracer_seq_ops);
        if (!*ret) {
                struct seq_file *m = file->private_data;
                m->private = iter;

                /* stop the trace while dumping */
                if (iter->tr->ctrl)
                        tracer_enabled = 0;

                if (iter->trace && iter->trace->open)
                        iter->trace->open(iter);
        } else {
                kfree(iter);
                iter = NULL;
        }
        mutex_unlock(&trace_types_lock);

 out:
        return iter;
}

int tracing_open_generic(struct inode *inode, struct file *filp)
{
        if (tracing_disabled)
                return -ENODEV;

        filp->private_data = inode->i_private;
        return 0;
}

int tracing_release(struct inode *inode, struct file *file)
{
        struct seq_file *m = (struct seq_file *)file->private_data;
        struct trace_iterator *iter = m->private;

        mutex_lock(&trace_types_lock);
        if (iter->trace && iter->trace->close)
                iter->trace->close(iter);

        /* reenable tracing if it was previously enabled */
        if (iter->tr->ctrl)
                tracer_enabled = 1;
        mutex_unlock(&trace_types_lock);

        seq_release(inode, file);
        kfree(iter);
        return 0;
}

static int tracing_open(struct inode *inode, struct file *file)
{
        int ret;

        __tracing_open(inode, file, &ret);

        return ret;
}

static int tracing_lt_open(struct inode *inode, struct file *file)
{
        struct trace_iterator *iter;
        int ret;

        iter = __tracing_open(inode, file, &ret);

        if (!ret)
                iter->iter_flags |= TRACE_FILE_LAT_FMT;

        return ret;
}


static void notrace *
t_next(struct seq_file *m, void *v, loff_t *pos)
{
        struct tracer *t = m->private;

        (*pos)++;

        if (t)
                t = t->next;

        m->private = t;

        return t;
}

static void *t_start(struct seq_file *m, loff_t *pos)
{
        struct tracer *t = m->private;
        loff_t l = 0;

        mutex_lock(&trace_types_lock);
        for (; t && l < *pos; t = t_next(m, t, &l))
                ;

        return t;
}

static void t_stop(struct seq_file *m, void *p)
{
        mutex_unlock(&trace_types_lock);
}

static int t_show(struct seq_file *m, void *v)
{
        struct tracer *t = v;

        if (!t)
                return 0;

        seq_printf(m, "%s", t->name);
        if (t->next)
                seq_putc(m, ' ');
        else
                seq_putc(m, '\n');

        return 0;
}

static struct seq_operations show_traces_seq_ops = {
        .start = t_start,
        .next = t_next,
        .stop = t_stop,
        .show = t_show,
};

static int show_traces_open(struct inode *inode, struct file *file)
{
        int ret;

        if (tracing_disabled)
                return -ENODEV;

        ret = seq_open(file, &show_traces_seq_ops);
        if (!ret) {
                struct seq_file *m = file->private_data;
                m->private = trace_types;
        }

        return ret;
}

static struct file_operations tracing_fops = {
        .open = tracing_open,
        .read = seq_read,
        .llseek = seq_lseek,
        .release = tracing_release,
};

static struct file_operations tracing_lt_fops = {
        .open = tracing_lt_open,
        .read = seq_read,
        .llseek = seq_lseek,
        .release = tracing_release,
};

static struct file_operations show_traces_fops = {
        .open = show_traces_open,
        .read = seq_read,
        .release = seq_release,
};

static ssize_t
tracing_iter_ctrl_read(struct file *filp, char __user *ubuf,
                       size_t cnt, loff_t *ppos)
{
        char *buf;
        int r = 0;
        int len = 0;
        int i;

        /* calulate max size */
        for (i = 0; trace_options[i]; i++) {
                len += strlen(trace_options[i]);
                len += 3; /* "no" and space */
        }

        /* +2 for \n and \0 */
        buf = kmalloc(len + 2, GFP_KERNEL);
        if (!buf)
                return -ENOMEM;

        for (i = 0; trace_options[i]; i++) {
                if (trace_flags & (1 << i))
                        r += sprintf(buf + r, "%s ", trace_options[i]);
                else
                        r += sprintf(buf + r, "no%s ", trace_options[i]);
        }

        r += sprintf(buf + r, "\n");
        WARN_ON(r >= len + 2);

        r = simple_read_from_buffer(ubuf, cnt, ppos,
                                    buf, r);

        kfree(buf);

        return r;
}

static ssize_t
tracing_iter_ctrl_write(struct file *filp, const char __user *ubuf,
                        size_t cnt, loff_t *ppos)
{
        char buf[64];
        char *cmp = buf;
        int neg = 0;
        int i;

        if (cnt > 63)
                cnt = 63;

        if (copy_from_user(&buf, ubuf, cnt))
                return -EFAULT;

        buf[cnt] = 0;

        if (strncmp(buf, "no", 2) == 0) {
                neg = 1;
                cmp += 2;
        }

        for (i = 0; trace_options[i]; i++) {
                int len = strlen(trace_options[i]);

                if (strncmp(cmp, trace_options[i], len) == 0) {
                        if (neg)
                                trace_flags &= ~(1 << i);
                        else
                                trace_flags |= (1 << i);
                        break;
                }
        }

        filp->f_pos += cnt;

        return cnt;
}

static struct file_operations tracing_iter_fops = {
        .open = tracing_open_generic,
        .read = tracing_iter_ctrl_read,
        .write = tracing_iter_ctrl_write,
};

static const char readme_msg[] =
        "tracing mini-HOWTO:\n\n"
        "# mkdir /debug\n"
        "# mount -t debugfs nodev /debug\n\n"
        "# cat /debug/tracing/available_tracers\n"
        "wakeup preemptirqsoff preemptoff irqsoff ftrace sched_switch none\n\n"
        "# cat /debug/tracing/current_tracer\n"
        "none\n"
        "# echo sched_switch > /debug/tracing/current_tracer\n"
        "# cat /debug/tracing/current_tracer\n"
        "sched_switch\n"
        "# cat /debug/tracing/iter_ctrl\n"
        "noprint-parent nosym-offset nosym-addr noverbose\n"
        "# echo print-parent > /debug/tracing/iter_ctrl\n"
        "# echo 1 > /debug/tracing/tracing_enabled\n"
        "# cat /debug/tracing/trace > /tmp/trace.txt\n"
        "echo 0 > /debug/tracing/tracing_enabled\n"
;

static ssize_t
tracing_readme_read(struct file *filp, char __user *ubuf,
                       size_t cnt, loff_t *ppos)
{
        return simple_read_from_buffer(ubuf, cnt, ppos,
                                        readme_msg, strlen(readme_msg));
}

static struct file_operations tracing_readme_fops = {
        .open = tracing_open_generic,
        .read = tracing_readme_read,
};


static ssize_t
tracing_ctrl_read(struct file *filp, char __user *ubuf,
                  size_t cnt, loff_t *ppos)
{
        struct trace_array *tr = filp->private_data;
        char buf[64];
        int r;

        r = sprintf(buf, "%ld\n", tr->ctrl);
        return simple_read_from_buffer(ubuf, cnt, ppos,
                                       buf, r);
}

static ssize_t
tracing_ctrl_write(struct file *filp, const char __user *ubuf,
                   size_t cnt, loff_t *ppos)
{
        struct trace_array *tr = filp->private_data;
        long val;
        char buf[64];

        if (cnt > 63)
                cnt = 63;

        if (copy_from_user(&buf, ubuf, cnt))
                return -EFAULT;

        buf[cnt] = 0;

        val = simple_strtoul(buf, NULL, 10);

        val = !!val;

        mutex_lock(&trace_types_lock);
        if (tr->ctrl ^ val) {
                if (val)
                        tracer_enabled = 1;
                else
                        tracer_enabled = 0;

                tr->ctrl = val;

                if (current_trace && current_trace->ctrl_update)
                        current_trace->ctrl_update(tr);
        }
        mutex_unlock(&trace_types_lock);

        filp->f_pos += cnt;

        return cnt;
}

static ssize_t
tracing_set_trace_read(struct file *filp, char __user *ubuf,
                       size_t cnt, loff_t *ppos)
{
        char buf[max_tracer_type_len+2];
        int r;

        mutex_lock(&trace_types_lock);
        if (current_trace)
                r = sprintf(buf, "%s\n", current_trace->name);
        else
                r = sprintf(buf, "\n");
        mutex_unlock(&trace_types_lock);

        return simple_read_from_buffer(ubuf, cnt, ppos,
                                       buf, r);
}

static ssize_t
tracing_set_trace_write(struct file *filp, const char __user *ubuf,
                        size_t cnt, loff_t *ppos)
{
        struct trace_array *tr = &global_trace;
        struct tracer *t;
        char buf[max_tracer_type_len+1];
        int i;

        if (cnt > max_tracer_type_len)
                cnt = max_tracer_type_len;

        if (copy_from_user(&buf, ubuf, cnt))
                return -EFAULT;

        buf[cnt] = 0;

        /* strip ending whitespace. */
        for (i = cnt - 1; i > 0 && isspace(buf[i]); i--)
                buf[i] = 0;

        mutex_lock(&trace_types_lock);
        for (t = trace_types; t; t = t->next) {
                if (strcmp(t->name, buf) == 0)
                        break;
        }
        if (!t || t == current_trace)
                goto out;

        if (current_trace && current_trace->reset)
                current_trace->reset(tr);

        current_trace = t;
        if (t->init)
                t->init(tr);

 out:
        mutex_unlock(&trace_types_lock);

        filp->f_pos += cnt;

        return cnt;
}

static ssize_t
tracing_max_lat_read(struct file *filp, char __user *ubuf,
                     size_t cnt, loff_t *ppos)
{
        unsigned long *ptr = filp->private_data;
        char buf[64];
        int r;

        r = snprintf(buf, 64, "%ld\n",
                     *ptr == (unsigned long)-1 ? -1 : nsecs_to_usecs(*ptr));
        if (r > 64)
                r = 64;
        return simple_read_from_buffer(ubuf, cnt, ppos,
                                       buf, r);
}

static ssize_t
tracing_max_lat_write(struct file *filp, const char __user *ubuf,
                      size_t cnt, loff_t *ppos)
{
        long *ptr = filp->private_data;
        long val;
        char buf[64];

        if (cnt > 63)
                cnt = 63;

        if (copy_from_user(&buf, ubuf, cnt))
                return -EFAULT;

        buf[cnt] = 0;

        val = simple_strtoul(buf, NULL, 10);

        *ptr = val * 1000;

        return cnt;
}

static struct file_operations tracing_max_lat_fops = {
        .open = tracing_open_generic,
        .read = tracing_max_lat_read,
        .write = tracing_max_lat_write,
};

static struct file_operations tracing_ctrl_fops = {
        .open = tracing_open_generic,
        .read = tracing_ctrl_read,
        .write = tracing_ctrl_write,
};

static struct file_operations set_tracer_fops = {
        .open = tracing_open_generic,
        .read = tracing_set_trace_read,
        .write = tracing_set_trace_write,
};

#ifdef CONFIG_DYNAMIC_FTRACE

static ssize_t
tracing_read_long(struct file *filp, char __user *ubuf,
                  size_t cnt, loff_t *ppos)
{
        unsigned long *p = filp->private_data;
        char buf[64];
        int r;

        r = sprintf(buf, "%ld\n", *p);
        return simple_read_from_buffer(ubuf, cnt, ppos,
                                       buf, r);
}

static struct file_operations tracing_read_long_fops = {
        .open = tracing_open_generic,
        .read = tracing_read_long,
};
#endif

static struct dentry *d_tracer;

struct dentry *tracing_init_dentry(void)
{
        static int once;

        if (d_tracer)
                return d_tracer;

        d_tracer = debugfs_create_dir("tracing", NULL);

        if (!d_tracer && !once) {
                once = 1;
                pr_warning("Could not create debugfs directory 'tracing'\n");
                return NULL;
        }

        return d_tracer;
}

#ifdef CONFIG_FTRACE_SELFTEST
/* Let selftest have access to static functions in this file */
#include "trace_selftest.c"
#endif

static __init void tracer_init_debugfs(void)
{
        struct dentry *d_tracer;
        struct dentry *entry;

        d_tracer = tracing_init_dentry();

        entry = debugfs_create_file("tracing_enabled", 0644, d_tracer,
                                    &global_trace, &tracing_ctrl_fops);
        if (!entry)
                pr_warning("Could not create debugfs 'tracing_enabled' entry\n");

        entry = debugfs_create_file("iter_ctrl", 0644, d_tracer,
                                    NULL, &tracing_iter_fops);
        if (!entry)
                pr_warning("Could not create debugfs 'iter_ctrl' entry\n");

        entry = debugfs_create_file("latency_trace", 0444, d_tracer,
                                    &global_trace, &tracing_lt_fops);
        if (!entry)
                pr_warning("Could not create debugfs 'latency_trace' entry\n");

        entry = debugfs_create_file("trace", 0444, d_tracer,
                                    &global_trace, &tracing_fops);
        if (!entry)
                pr_warning("Could not create debugfs 'trace' entry\n");

        entry = debugfs_create_file("available_tracers", 0444, d_tracer,
                                    &global_trace, &show_traces_fops);
        if (!entry)
                pr_warning("Could not create debugfs 'trace' entry\n");

        entry = debugfs_create_file("current_tracer", 0444, d_tracer,
                                    &global_trace, &set_tracer_fops);
        if (!entry)
                pr_warning("Could not create debugfs 'trace' entry\n");

        entry = debugfs_create_file("tracing_max_latency", 0644, d_tracer,
                                    &tracing_max_latency,
                                    &tracing_max_lat_fops);
        if (!entry)
                pr_warning("Could not create debugfs "
                           "'tracing_max_latency' entry\n");

        entry = debugfs_create_file("tracing_thresh", 0644, d_tracer,
                                    &tracing_thresh, &tracing_max_lat_fops);
        if (!entry)
                pr_warning("Could not create debugfs "
                           "'tracing_threash' entry\n");
        entry = debugfs_create_file("README", 0644, d_tracer,
                                    NULL, &tracing_readme_fops);
        if (!entry)
                pr_warning("Could not create debugfs 'README' entry\n");


#ifdef CONFIG_DYNAMIC_FTRACE
        entry = debugfs_create_file("dyn_ftrace_total_info", 0444, d_tracer,
                                    &ftrace_update_tot_cnt,
                                    &tracing_read_long_fops);
        if (!entry)
                pr_warning("Could not create debugfs "
                           "'dyn_ftrace_total_info' entry\n");
#endif
}

/* dummy trace to disable tracing */
static struct tracer no_tracer __read_mostly =
{
        .name = "none",
};

static int trace_alloc_page(void)
{
        struct trace_array_cpu *data;
        struct page *page, *tmp;
        LIST_HEAD(pages);
        void *array;
        int i;

        /* first allocate a page for each CPU */
        for_each_possible_cpu(i) {
                array = (void *)__get_free_page(GFP_KERNEL);
                if (array == NULL) {
                        printk(KERN_ERR "tracer: failed to allocate page"
                               "for trace buffer!\n");
                        goto free_pages;
                }

                page = virt_to_page(array);
                list_add(&page->lru, &pages);

/* Only allocate if we are actually using the max trace */
#ifdef CONFIG_TRACER_MAX_TRACE
                array = (void *)__get_free_page(GFP_KERNEL);
                if (array == NULL) {
                        printk(KERN_ERR "tracer: failed to allocate page"
                               "for trace buffer!\n");
                        goto free_pages;
                }
                page = virt_to_page(array);
                list_add(&page->lru, &pages);
#endif
        }

        /* Now that we successfully allocate a page per CPU, add them */
        for_each_possible_cpu(i) {
                data = global_trace.data[i];
                page = list_entry(pages.next, struct page, lru);
                list_del_init(&page->lru);
                list_add_tail(&page->lru, &data->trace_pages);
                ClearPageLRU(page);

#ifdef CONFIG_TRACER_MAX_TRACE
                data = max_tr.data[i];
                page = list_entry(pages.next, struct page, lru);
                list_del_init(&page->lru);
                list_add_tail(&page->lru, &data->trace_pages);
                SetPageLRU(page);
#endif
        }
        global_trace.entries += ENTRIES_PER_PAGE;

        return 0;

 free_pages:
        list_for_each_entry_safe(page, tmp, &pages, lru) {
                list_del_init(&page->lru);
                __free_page(page);
        }
        return -ENOMEM;
}

__init static int tracer_alloc_buffers(void)
{
        struct trace_array_cpu *data;
        void *array;
        struct page *page;
        int pages = 0;
        int ret = -ENOMEM;
        int i;

        /* Allocate the first page for all buffers */
        for_each_possible_cpu(i) {
                data = global_trace.data[i] = &per_cpu(global_trace_cpu, i);
                max_tr.data[i] = &per_cpu(max_data, i);

                array = (void *)__get_free_page(GFP_KERNEL);
                if (array == NULL) {
                        printk(KERN_ERR "tracer: failed to allocate page"
                               "for trace buffer!\n");
                        goto free_buffers;
                }

                /* set the array to the list */
                INIT_LIST_HEAD(&data->trace_pages);
                page = virt_to_page(array);
                list_add(&page->lru, &data->trace_pages);
                /* use the LRU flag to differentiate the two buffers */
                ClearPageLRU(page);

/* Only allocate if we are actually using the max trace */
#ifdef CONFIG_TRACER_MAX_TRACE
                array = (void *)__get_free_page(GFP_KERNEL);
                if (array == NULL) {
                        printk(KERN_ERR "tracer: failed to allocate page"
                               "for trace buffer!\n");
                        goto free_buffers;
                }

                INIT_LIST_HEAD(&max_tr.data[i]->trace_pages);
                page = virt_to_page(array);
                list_add(&page->lru, &max_tr.data[i]->trace_pages);
                SetPageLRU(page);
#endif
        }

        /*
         * Since we allocate by orders of pages, we may be able to
         * round up a bit.
         */
        global_trace.entries = ENTRIES_PER_PAGE;
        pages++;

        while (global_trace.entries < trace_nr_entries) {
                if (trace_alloc_page())
                        break;
                pages++;
        }
        max_tr.entries = global_trace.entries;

        pr_info("tracer: %d pages allocated for %ld",
                pages, trace_nr_entries);
        pr_info(" entries of %ld bytes\n", (long)TRACE_ENTRY_SIZE);
        pr_info("   actual entries %ld\n", global_trace.entries);

        tracer_init_debugfs();

        trace_init_cmdlines();

        register_tracer(&no_tracer);
        current_trace = &no_tracer;

        /* All seems OK, enable tracing */
        tracing_disabled = 0;

        return 0;

 free_buffers:
        for (i-- ; i >= 0; i--) {
                struct page *page, *tmp;
                struct trace_array_cpu *data = global_trace.data[i];

                if (data) {
                        list_for_each_entry_safe(page, tmp,
                                                 &data->trace_pages, lru) {
                                list_del_init(&page->lru);
                                __free_page(page);
                        }
                }

#ifdef CONFIG_TRACER_MAX_TRACE
                data = max_tr.data[i];
                if (data) {
                        list_for_each_entry_safe(page, tmp,
                                                 &data->trace_pages, lru) {
                                list_del_init(&page->lru);
                                __free_page(page);
                        }
                }
#endif
        }
        return ret;
}

fs_initcall(tracer_alloc_buffers);