trace_stack.c

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/*
 * Copyright (C) 2008 Steven Rostedt <[email protected]>
 *
 */
#include <linux/stacktrace.h>
#include <linux/kallsyms.h>
#include <linux/seq_file.h>
#include <linux/spinlock.h>
#include <linux/uaccess.h>
#include <linux/debugfs.h>
#include <linux/ftrace.h>
#include <linux/module.h>
#include <linux/sysctl.h>
#include <linux/init.h>
#include <linux/fs.h>

#include <asm/setup.h>

#include "trace.h"

#define STACK_TRACE_ENTRIES 500

static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES+1] =
     { [0 ... (STACK_TRACE_ENTRIES)] = ULONG_MAX };
static unsigned stack_dump_index[STACK_TRACE_ENTRIES];

static struct stack_trace max_stack_trace = {
    .max_entries        = STACK_TRACE_ENTRIES,
    .entries        = stack_dump_trace,
};

static unsigned long max_stack_size;
static arch_spinlock_t max_stack_lock =
    (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;

static int stack_trace_disabled __read_mostly;
static DEFINE_PER_CPU(int, trace_active);
static DEFINE_MUTEX(stack_sysctl_mutex);

int stack_tracer_enabled;
static int last_stack_tracer_enabled;

static inline void check_stack(void)
{
    unsigned long this_size, flags;
    unsigned long *p, *top, *start;
    int i;

    this_size = ((unsigned long)&this_size) & (THREAD_SIZE-1);
    this_size = THREAD_SIZE - this_size;

    if (this_size <= max_stack_size)
        return;

    /* we do not handle interrupt stacks yet */
    if (!object_is_on_stack(&this_size))
        return;

    local_irq_save(flags);
    arch_spin_lock(&max_stack_lock);

    /* a race could have already updated it */
    if (this_size <= max_stack_size)
        goto out;

    max_stack_size = this_size;

    max_stack_trace.nr_entries  = 0;
    max_stack_trace.skip        = 3;

    save_stack_trace(&max_stack_trace);

    /*
     * Now find where in the stack these are.
     */
    i = 0;
    start = &this_size;
    top = (unsigned long *)
        (((unsigned long)start & ~(THREAD_SIZE-1)) + THREAD_SIZE);

    /*
     * Loop through all the entries. One of the entries may
     * for some reason be missed on the stack, so we may
     * have to account for them. If they are all there, this
     * loop will only happen once. This code only takes place
     * on a new max, so it is far from a fast path.
     */
    while (i < max_stack_trace.nr_entries) {
        int found = 0;

        stack_dump_index[i] = this_size;
        p = start;

        for (; p < top && i < max_stack_trace.nr_entries; p++) {
            if (*p == stack_dump_trace[i]) {
                this_size = stack_dump_index[i++] =
                    (top - p) * sizeof(unsigned long);
                found = 1;
                /* Start the search from here */
                start = p + 1;
            }
        }

        if (!found)
            i++;
    }

 out:
    arch_spin_unlock(&max_stack_lock);
    local_irq_restore(flags);
}

static void
stack_trace_call(unsigned long ip, unsigned long parent_ip,
         struct ftrace_ops *op, struct pt_regs *pt_regs)
{
    int cpu;

    if (unlikely(!ftrace_enabled || stack_trace_disabled))
        return;

    preempt_disable_notrace();

    cpu = raw_smp_processor_id();
    /* no atomic needed, we only modify this variable by this cpu */
    if (per_cpu(trace_active, cpu)++ != 0)
        goto out;

    check_stack();

 out:
    per_cpu(trace_active, cpu)--;
    /* prevent recursion in schedule */
    preempt_enable_notrace();
}

static struct ftrace_ops trace_ops __read_mostly =
{
    .func = stack_trace_call,
    .flags = FTRACE_OPS_FL_RECURSION_SAFE,
};

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

    r = snprintf(buf, sizeof(buf), "%ld\n", *ptr);
    if (r > sizeof(buf))
        r = sizeof(buf);
    return simple_read_from_buffer(ubuf, count, ppos, buf, r);
}

static ssize_t
stack_max_size_write(struct file *filp, const char __user *ubuf,
             size_t count, loff_t *ppos)
{
    long *ptr = filp->private_data;
    unsigned long val, flags;
    int ret;
    int cpu;

    ret = kstrtoul_from_user(ubuf, count, 10, &val);
    if (ret)
        return ret;

    local_irq_save(flags);

    /*
     * In case we trace inside arch_spin_lock() or after (NMI),
     * we will cause circular lock, so we also need to increase
     * the percpu trace_active here.
     */
    cpu = smp_processor_id();
    per_cpu(trace_active, cpu)++;

    arch_spin_lock(&max_stack_lock);
    *ptr = val;
    arch_spin_unlock(&max_stack_lock);

    per_cpu(trace_active, cpu)--;
    local_irq_restore(flags);

    return count;
}

static const struct file_operations stack_max_size_fops = {
    .open       = tracing_open_generic,
    .read       = stack_max_size_read,
    .write      = stack_max_size_write,
    .llseek     = default_llseek,
};

static void *
__next(struct seq_file *m, loff_t *pos)
{
    long n = *pos - 1;

    if (n >= max_stack_trace.nr_entries || stack_dump_trace[n] == ULONG_MAX)
        return NULL;

    m->private = (void *)n;
    return &m->private;
}

static void *
t_next(struct seq_file *m, void *v, loff_t *pos)
{
    (*pos)++;
    return __next(m, pos);
}

static void *t_start(struct seq_file *m, loff_t *pos)
{
    int cpu;

    local_irq_disable();

    cpu = smp_processor_id();
    per_cpu(trace_active, cpu)++;

    arch_spin_lock(&max_stack_lock);

    if (*pos == 0)
        return SEQ_START_TOKEN;

    return __next(m, pos);
}

static void t_stop(struct seq_file *m, void *p)
{
    int cpu;

    arch_spin_unlock(&max_stack_lock);

    cpu = smp_processor_id();
    per_cpu(trace_active, cpu)--;

    local_irq_enable();
}

static int trace_lookup_stack(struct seq_file *m, long i)
{
    unsigned long addr = stack_dump_trace[i];

    return seq_printf(m, "%pS\n", (void *)addr);
}

static void print_disabled(struct seq_file *m)
{
    seq_puts(m, "#\n"
         "#  Stack tracer disabled\n"
         "#\n"
         "# To enable the stack tracer, either add 'stacktrace' to the\n"
         "# kernel command line\n"
         "# or 'echo 1 > /proc/sys/kernel/stack_tracer_enabled'\n"
         "#\n");
}

static int t_show(struct seq_file *m, void *v)
{
    long i;
    int size;

    if (v == SEQ_START_TOKEN) {
        seq_printf(m, "        Depth    Size   Location"
               "    (%d entries)\n"
               "        -----    ----   --------\n",
               max_stack_trace.nr_entries - 1);

        if (!stack_tracer_enabled && !max_stack_size)
            print_disabled(m);

        return 0;
    }

    i = *(long *)v;

    if (i >= max_stack_trace.nr_entries ||
        stack_dump_trace[i] == ULONG_MAX)
        return 0;

    if (i+1 == max_stack_trace.nr_entries ||
        stack_dump_trace[i+1] == ULONG_MAX)
        size = stack_dump_index[i];
    else
        size = stack_dump_index[i] - stack_dump_index[i+1];

    seq_printf(m, "%3ld) %8d   %5d   ", i, stack_dump_index[i], size);

    trace_lookup_stack(m, i);

    return 0;
}

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

static int stack_trace_open(struct inode *inode, struct file *file)
{
    return seq_open(file, &stack_trace_seq_ops);
}

static const struct file_operations stack_trace_fops = {
    .open       = stack_trace_open,
    .read       = seq_read,
    .llseek     = seq_lseek,
    .release    = seq_release,
};

static int
stack_trace_filter_open(struct inode *inode, struct file *file)
{
    return ftrace_regex_open(&trace_ops, FTRACE_ITER_FILTER,
                 inode, file);
}

static const struct file_operations stack_trace_filter_fops = {
    .open = stack_trace_filter_open,
    .read = seq_read,
    .write = ftrace_filter_write,
    .llseek = ftrace_regex_lseek,
    .release = ftrace_regex_release,
};

int
stack_trace_sysctl(struct ctl_table *table, int write,
           void __user *buffer, size_t *lenp,
           loff_t *ppos)
{
    int ret;

    mutex_lock(&stack_sysctl_mutex);

    ret = proc_dointvec(table, write, buffer, lenp, ppos);

    if (ret || !write ||
        (last_stack_tracer_enabled == !!stack_tracer_enabled))
        goto out;

    last_stack_tracer_enabled = !!stack_tracer_enabled;

    if (stack_tracer_enabled)
        register_ftrace_function(&trace_ops);
    else
        unregister_ftrace_function(&trace_ops);

 out:
    mutex_unlock(&stack_sysctl_mutex);
    return ret;
}

static char stack_trace_filter_buf[COMMAND_LINE_SIZE+1] __initdata;

static __init int enable_stacktrace(char *str)
{
    if (strncmp(str, "_filter=", 8) == 0)
        strncpy(stack_trace_filter_buf, str+8, COMMAND_LINE_SIZE);

    stack_tracer_enabled = 1;
    last_stack_tracer_enabled = 1;
    return 1;
}
__setup("stacktrace", enable_stacktrace);

static __init int stack_trace_init(void)
{
    struct dentry *d_tracer;

    d_tracer = tracing_init_dentry();

    trace_create_file("stack_max_size", 0644, d_tracer,
            &max_stack_size, &stack_max_size_fops);

    trace_create_file("stack_trace", 0444, d_tracer,
            NULL, &stack_trace_fops);

    trace_create_file("stack_trace_filter", 0444, d_tracer,
            NULL, &stack_trace_filter_fops);

    if (stack_trace_filter_buf[0])
        ftrace_set_early_filter(&trace_ops, stack_trace_filter_buf, 1);

    if (stack_tracer_enabled)
        register_ftrace_function(&trace_ops);

    return 0;
}

device_initcall(stack_trace_init);