init/main.c: Give init_task a canary

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

/*
 * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
 *
 */
#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

#ifdef CC_USING_FENTRY
# define fentry         1
#else
# define fentry         0
#endif

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

/*
 * Reserve one entry for the passed in ip. This will allow
 * us to remove most or all of the stack size overhead
 * added by the stack tracer itself.
 */
static struct stack_trace max_stack_trace = {
        .max_entries            = STACK_TRACE_ENTRIES - 1,
        .entries                = &stack_dump_trace[1],
};

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

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 print_max_stack(void)
{
        long i;
        int size;

        pr_emerg("        Depth    Size   Location    (%d entries)\n"
                           "        -----    ----   --------\n",
                           max_stack_trace.nr_entries - 1);

        for (i = 0; i < max_stack_trace.nr_entries; i++) {
                if (stack_dump_trace[i] == ULONG_MAX)
                        break;
                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];

                pr_emerg("%3ld) %8d   %5d   %pS\n", i, stack_dump_index[i],
                                size, (void *)stack_dump_trace[i]);
        }
}

static inline void
check_stack(unsigned long ip, unsigned long *stack)
{
        unsigned long this_size, flags; unsigned long *p, *top, *start;
        static int tracer_frame;
        int frame_size = ACCESS_ONCE(tracer_frame);
        int i;

        this_size = ((unsigned long)stack) & (THREAD_SIZE-1);
        this_size = THREAD_SIZE - this_size;
        /* Remove the frame of the tracer */
        this_size -= frame_size;

        if (this_size <= max_stack_size)
                return;

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

        local_irq_save(flags);
        arch_spin_lock(&max_stack_lock);

        /* In case another CPU set the tracer_frame on us */
        if (unlikely(!frame_size))
                this_size -= tracer_frame;

        /* 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;

        if (using_ftrace_ops_list_func())
                max_stack_trace.skip = 4;
        else
                max_stack_trace.skip = 3;

        save_stack_trace(&max_stack_trace);

        /*
         * Add the passed in ip from the function tracer.
         * Searching for this on the stack will skip over
         * most of the overhead from the stack tracer itself.
         */
        stack_dump_trace[0] = ip;
        max_stack_trace.nr_entries++;

        /*
         * Now find where in the stack these are.
         */
        i = 0;
        start = stack;
        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;
                                /*
                                 * We do not want to show the overhead
                                 * of the stack tracer stack in the
                                 * max stack. If we haven't figured
                                 * out what that is, then figure it out
                                 * now.
                                 */
                                if (unlikely(!tracer_frame) && i == 1) {
                                        tracer_frame = (p - stack) *
                                                sizeof(unsigned long);
                                        max_stack_size -= tracer_frame;
                                }
                        }
                }

                if (!found)
                        i++;
        }

        if (*end_of_stack(current) != STACK_END_MAGIC) {
                print_max_stack();
                BUG();
        }

 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)
{
        unsigned long stack;
        int cpu;

        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;

        /*
         * When fentry is used, the traced function does not get
         * its stack frame set up, and we lose the parent.
         * The ip is pretty useless because the function tracer
         * was called before that function set up its stack frame.
         * In this case, we use the parent ip.
         *
         * By adding the return address of either the parent ip
         * or the current ip we can disregard most of the stack usage
         * caused by the stack tracer itself.
         *
         * The function tracer always reports the address of where the
         * mcount call was, but the stack will hold the return address.
         */
        if (fentry)
                ip = parent_ip;
        else
                ip += MCOUNT_INSN_SIZE;

        check_stack(ip, &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 = tracing_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();
        if (!d_tracer)
                return 0;

        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);