/*
 * Performance events callchain code, extracted from core.c:
 *
 *  Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
 *  Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
 *  Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra
 *  Copyright  ©  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
 *
 * For licensing details see kernel-base/COPYING
 */

#include <linux/perf_event.h>
#include <linux/slab.h>
#include "internal.h"

struct callchain_cpus_entries {
        struct rcu_head                 rcu_head;
        struct perf_callchain_entry     *cpu_entries[0];
};

int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH;
int sysctl_perf_event_max_contexts_per_stack __read_mostly = PERF_MAX_CONTEXTS_PER_STACK;

static inline size_t perf_callchain_entry__sizeof(void)
{
        return (sizeof(struct perf_callchain_entry) +
                sizeof(__u64) * (sysctl_perf_event_max_stack +
                                 sysctl_perf_event_max_contexts_per_stack));
}

static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]);
static atomic_t nr_callchain_events;
static DEFINE_MUTEX(callchain_mutex);
static struct callchain_cpus_entries *callchain_cpus_entries;


__weak void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
                                  struct pt_regs *regs)
{
}

__weak void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
                                struct pt_regs *regs)
{
}

static void release_callchain_buffers_rcu(struct rcu_head *head)
{
        struct callchain_cpus_entries *entries;
        int cpu;

        entries = container_of(head, struct callchain_cpus_entries, rcu_head);

        for_each_possible_cpu(cpu)
                kfree(entries->cpu_entries[cpu]);

        kfree(entries);
}

static void release_callchain_buffers(void)
{
        struct callchain_cpus_entries *entries;

        entries = callchain_cpus_entries;
        RCU_INIT_POINTER(callchain_cpus_entries, NULL);
        call_rcu(&entries->rcu_head, release_callchain_buffers_rcu);
}

static int alloc_callchain_buffers(void)
{
        int cpu;
        int size;
        struct callchain_cpus_entries *entries;

        /*
         * We can't use the percpu allocation API for data that can be
         * accessed from NMI. Use a temporary manual per cpu allocation
         * until that gets sorted out.
         */
        size = offsetof(struct callchain_cpus_entries, cpu_entries[nr_cpu_ids]);

        entries = kzalloc(size, GFP_KERNEL);
        if (!entries)
                return -ENOMEM;

        size = perf_callchain_entry__sizeof() * PERF_NR_CONTEXTS;

        for_each_possible_cpu(cpu) {
                entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL,
                                                         cpu_to_node(cpu));
                if (!entries->cpu_entries[cpu])
                        goto fail;
        }

        rcu_assign_pointer(callchain_cpus_entries, entries);

        return 0;

fail:
        for_each_possible_cpu(cpu)
                kfree(entries->cpu_entries[cpu]);
        kfree(entries);

        return -ENOMEM;
}

int get_callchain_buffers(int event_max_stack)
{
        int err = 0;
        int count;

        mutex_lock(&callchain_mutex);

        count = atomic_inc_return(&nr_callchain_events);
        if (WARN_ON_ONCE(count < 1)) {
                err = -EINVAL;
                goto exit;
        }

        if (count > 1) {
                /* If the allocation failed, give up */
                if (!callchain_cpus_entries)
                        err = -ENOMEM;
                /*
                 * If requesting per event more than the global cap,
                 * return a different error to help userspace figure
                 * this out.
                 *
                 * And also do it here so that we have &callchain_mutex held.
                 */
                if (event_max_stack > sysctl_perf_event_max_stack)
                        err = -EOVERFLOW;
                goto exit;
        }

        err = alloc_callchain_buffers();
exit:
        if (err)
                atomic_dec(&nr_callchain_events);

        mutex_unlock(&callchain_mutex);

        return err;
}

void put_callchain_buffers(void)
{
        if (atomic_dec_and_mutex_lock(&nr_callchain_events, &callchain_mutex)) {
                release_callchain_buffers();
                mutex_unlock(&callchain_mutex);
        }
}

static struct perf_callchain_entry *get_callchain_entry(int *rctx)
{
        int cpu;
        struct callchain_cpus_entries *entries;

        *rctx = get_recursion_context(this_cpu_ptr(callchain_recursion));
        if (*rctx == -1)
                return NULL;

        entries = rcu_dereference(callchain_cpus_entries);
        if (!entries)
                return NULL;

        cpu = smp_processor_id();

        return (((void *)entries->cpu_entries[cpu]) +
                (*rctx * perf_callchain_entry__sizeof()));
}

static void
put_callchain_entry(int rctx)
{
        put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
}

struct perf_callchain_entry *
perf_callchain(struct perf_event *event, struct pt_regs *regs)
{
        bool kernel = !event->attr.exclude_callchain_kernel;
        bool user   = !event->attr.exclude_callchain_user;
        /* Disallow cross-task user callchains. */
        bool crosstask = event->ctx->task && event->ctx->task != current;
        const u32 max_stack = event->attr.sample_max_stack;

        if (!kernel && !user)
                return NULL;

        return get_perf_callchain(regs, 0, kernel, user, max_stack, crosstask, true);
}

struct perf_callchain_entry *
get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
                   u32 max_stack, bool crosstask, bool add_mark)
{
        struct perf_callchain_entry *entry;
        struct perf_callchain_entry_ctx ctx;
        int rctx;

        entry = get_callchain_entry(&rctx);
        if (rctx == -1)
                return NULL;

        if (!entry)
                goto exit_put;

        ctx.entry     = entry;
        ctx.max_stack = max_stack;
        ctx.nr        = entry->nr = init_nr;
        ctx.contexts       = 0;
        ctx.contexts_maxed = false;

        if (kernel && !user_mode(regs)) {
                if (add_mark)
                        perf_callchain_store_context(&ctx, PERF_CONTEXT_KERNEL);
                perf_callchain_kernel(&ctx, regs);
        }

        if (user) {
                if (!user_mode(regs)) {
                        if  (current->mm)
                                regs = task_pt_regs(current);
                        else
                                regs = NULL;
                }

                if (regs) {
                        if (crosstask)
                                goto exit_put;

                        if (add_mark)
                                perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);
                        perf_callchain_user(&ctx, regs);
                }
        }

exit_put:
        put_callchain_entry(rctx);

        return entry;
}

/*
 * Used for sysctl_perf_event_max_stack and
 * sysctl_perf_event_max_contexts_per_stack.
 */
int perf_event_max_stack_handler(struct ctl_table *table, int write,
                                 void __user *buffer, size_t *lenp, loff_t *ppos)
{
        int *value = table->data;
        int new_value = *value, ret;
        struct ctl_table new_table = *table;

        new_table.data = &new_value;
        ret = proc_dointvec_minmax(&new_table, write, buffer, lenp, ppos);
        if (ret || !write)
                return ret;

        mutex_lock(&callchain_mutex);
        if (atomic_read(&nr_callchain_events))
                ret = -EBUSY;
        else
                *value = new_value;

        mutex_unlock(&callchain_mutex);

        return ret;
}