// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) 2021, Microsoft Corporation.
 *
 * Authors:
 *   Beau Belgrave <beaub@linux.microsoft.com>
 */

#include <linux/bitmap.h>
#include <linux/cdev.h>
#include <linux/hashtable.h>
#include <linux/list.h>
#include <linux/io.h>
#include <linux/uio.h>
#include <linux/ioctl.h>
#include <linux/jhash.h>
#include <linux/refcount.h>
#include <linux/trace_events.h>
#include <linux/tracefs.h>
#include <linux/types.h>
#include <linux/uaccess.h>
#include <linux/highmem.h>
#include <linux/init.h>
#include <linux/user_events.h>
#include "trace_dynevent.h"
#include "trace_output.h"
#include "trace.h"

#define USER_EVENTS_PREFIX_LEN (sizeof(USER_EVENTS_PREFIX)-1)

#define FIELD_DEPTH_TYPE 0
#define FIELD_DEPTH_NAME 1
#define FIELD_DEPTH_SIZE 2

/* Limit how long of an event name plus args within the subsystem. */
#define MAX_EVENT_DESC 512
#define EVENT_NAME(user_event) ((user_event)->reg_name)
#define EVENT_TP_NAME(user_event) ((user_event)->tracepoint.name)
#define MAX_FIELD_ARRAY_SIZE 1024

/*
 * Internal bits (kernel side only) to keep track of connected probes:
 * These are used when status is requested in text form about an event. These
 * bits are compared against an internal byte on the event to determine which
 * probes to print out to the user.
 *
 * These do not reflect the mapped bytes between the user and kernel space.
 */
#define EVENT_STATUS_FTRACE BIT(0)
#define EVENT_STATUS_PERF BIT(1)
#define EVENT_STATUS_OTHER BIT(7)

/*
 * Stores the system name, tables, and locks for a group of events. This
 * allows isolation for events by various means.
 */
struct user_event_group {
        char                    *system_name;
        char                    *system_multi_name;
        struct hlist_node       node;
        struct mutex            reg_mutex;
        DECLARE_HASHTABLE(register_table, 8);
        /* ID that moves forward within the group for multi-event names */
        u64                     multi_id;
};

/* Group for init_user_ns mapping, top-most group */
static struct user_event_group *init_group;

/* Max allowed events for the whole system */
static unsigned int max_user_events = 32768;

/* Current number of events on the whole system */
static unsigned int current_user_events;

/*
 * Stores per-event properties, as users register events
 * within a file a user_event might be created if it does not
 * already exist. These are globally used and their lifetime
 * is tied to the refcnt member. These cannot go away until the
 * refcnt reaches one.
 */
struct user_event {
        struct user_event_group         *group;
        char                            *reg_name;
        struct tracepoint               tracepoint;
        struct trace_event_call         call;
        struct trace_event_class        class;
        struct dyn_event                devent;
        struct hlist_node               node;
        struct list_head                fields;
        struct list_head                validators;
        struct work_struct              put_work;
        refcount_t                      refcnt;
        int                             min_size;
        int                             reg_flags;
        char                            status;
};

/*
 * Stores per-mm/event properties that enable an address to be
 * updated properly for each task. As tasks are forked, we use
 * these to track enablement sites that are tied to an event.
 */
struct user_event_enabler {
        struct list_head        mm_enablers_link;
        struct user_event       *event;
        unsigned long           addr;

        /* Track enable bit, flags, etc. Aligned for bitops. */
        unsigned long           values;
};

/* Bits 0-5 are for the bit to update upon enable/disable (0-63 allowed) */
#define ENABLE_VAL_BIT_MASK 0x3F

/* Bit 6 is for faulting status of enablement */
#define ENABLE_VAL_FAULTING_BIT 6

/* Bit 7 is for freeing status of enablement */
#define ENABLE_VAL_FREEING_BIT 7

/* Bit 8 is for marking 32-bit on 64-bit */
#define ENABLE_VAL_32_ON_64_BIT 8

#define ENABLE_VAL_COMPAT_MASK (1 << ENABLE_VAL_32_ON_64_BIT)

/* Only duplicate the bit and compat values */
#define ENABLE_VAL_DUP_MASK (ENABLE_VAL_BIT_MASK | ENABLE_VAL_COMPAT_MASK)

#define ENABLE_BITOPS(e) (&(e)->values)

#define ENABLE_BIT(e) ((int)((e)->values & ENABLE_VAL_BIT_MASK))

#define EVENT_MULTI_FORMAT(f) ((f) & USER_EVENT_REG_MULTI_FORMAT)

/* Used for asynchronous faulting in of pages */
struct user_event_enabler_fault {
        struct work_struct              work;
        struct user_event_mm            *mm;
        struct user_event_enabler       *enabler;
        int                             attempt;
};

static struct kmem_cache *fault_cache;

/* Global list of memory descriptors using user_events */
static LIST_HEAD(user_event_mms);
static DEFINE_SPINLOCK(user_event_mms_lock);

/*
 * Stores per-file events references, as users register events
 * within a file this structure is modified and freed via RCU.
 * The lifetime of this struct is tied to the lifetime of the file.
 * These are not shared and only accessible by the file that created it.
 */
struct user_event_refs {
        struct rcu_head         rcu;
        int                     count;
        struct user_event       *events[];
};

struct user_event_file_info {
        struct user_event_group *group;
        struct user_event_refs  *refs;
};

#define VALIDATOR_ENSURE_NULL (1 << 0)
#define VALIDATOR_REL (1 << 1)

struct user_event_validator {
        struct list_head        user_event_link;
        int                     offset;
        int                     flags;
};

static inline void align_addr_bit(unsigned long *addr, int *bit,
                                  unsigned long *flags)
{
        if (IS_ALIGNED(*addr, sizeof(long))) {
#ifdef __BIG_ENDIAN
                /* 32 bit on BE 64 bit requires a 32 bit offset when aligned. */
                if (test_bit(ENABLE_VAL_32_ON_64_BIT, flags))
                        *bit += 32;
#endif
                return;
        }

        *addr = ALIGN_DOWN(*addr, sizeof(long));

        /*
         * We only support 32 and 64 bit values. The only time we need
         * to align is a 32 bit value on a 64 bit kernel, which on LE
         * is always 32 bits, and on BE requires no change when unaligned.
         */
#ifdef __LITTLE_ENDIAN
        *bit += 32;
#endif
}

typedef void (*user_event_func_t) (struct user_event *user, struct iov_iter *i,
                                   void *tpdata, bool *faulted);

static int user_event_parse(struct user_event_group *group, char *name,
                            char *args, char *flags,
                            struct user_event **newuser, int reg_flags);

static struct user_event_mm *user_event_mm_get(struct user_event_mm *mm);
static struct user_event_mm *user_event_mm_get_all(struct user_event *user);
static void user_event_mm_put(struct user_event_mm *mm);
static int destroy_user_event(struct user_event *user);
static bool user_fields_match(struct user_event *user, int argc,
                              const char **argv);

static u32 user_event_key(char *name)
{
        return jhash(name, strlen(name), 0);
}

static bool user_event_capable(u16 reg_flags)
{
        /* Persistent events require CAP_PERFMON / CAP_SYS_ADMIN */
        if (reg_flags & USER_EVENT_REG_PERSIST) {
                if (!perfmon_capable())
                        return false;
        }

        return true;
}

static struct user_event *user_event_get(struct user_event *user)
{
        refcount_inc(&user->refcnt);

        return user;
}

static void delayed_destroy_user_event(struct work_struct *work)
{
        struct user_event *user = container_of(
                work, struct user_event, put_work);

        mutex_lock(&event_mutex);

        if (!refcount_dec_and_test(&user->refcnt))
                goto out;

        if (destroy_user_event(user)) {
                /*
                 * The only reason this would fail here is if we cannot
                 * update the visibility of the event. In this case the
                 * event stays in the hashtable, waiting for someone to
                 * attempt to delete it later.
                 */
                pr_warn("user_events: Unable to delete event\n");
                refcount_set(&user->refcnt, 1);
        }
out:
        mutex_unlock(&event_mutex);
}

static void user_event_put(struct user_event *user, bool locked)
{
        bool delete;

        if (unlikely(!user))
                return;

        /*
         * When the event is not enabled for auto-delete there will always
         * be at least 1 reference to the event. During the event creation
         * we initially set the refcnt to 2 to achieve this. In those cases
         * the caller must acquire event_mutex and after decrement check if
         * the refcnt is 1, meaning this is the last reference. When auto
         * delete is enabled, there will only be 1 ref, IE: refcnt will be
         * only set to 1 during creation to allow the below checks to go
         * through upon the last put. The last put must always be done with
         * the event mutex held.
         */
        if (!locked) {
                lockdep_assert_not_held(&event_mutex);
                delete = refcount_dec_and_mutex_lock(&user->refcnt, &event_mutex);
        } else {
                lockdep_assert_held(&event_mutex);
                delete = refcount_dec_and_test(&user->refcnt);
        }

        if (!delete)
                return;

        /*
         * We now have the event_mutex in all cases, which ensures that
         * no new references will be taken until event_mutex is released.
         * New references come through find_user_event(), which requires
         * the event_mutex to be held.
         */

        if (user->reg_flags & USER_EVENT_REG_PERSIST) {
                /* We should not get here when persist flag is set */
                pr_alert("BUG: Auto-delete engaged on persistent event\n");
                goto out;
        }

        /*
         * Unfortunately we have to attempt the actual destroy in a work
         * queue. This is because not all cases handle a trace_event_call
         * being removed within the class->reg() operation for unregister.
         */
        INIT_WORK(&user->put_work, delayed_destroy_user_event);

        /*
         * Since the event is still in the hashtable, we have to re-inc
         * the ref count to 1. This count will be decremented and checked
         * in the work queue to ensure it's still the last ref. This is
         * needed because a user-process could register the same event in
         * between the time of event_mutex release and the work queue
         * running the delayed destroy. If we removed the item now from
         * the hashtable, this would result in a timing window where a
         * user process would fail a register because the trace_event_call
         * register would fail in the tracing layers.
         */
        refcount_set(&user->refcnt, 1);

        if (WARN_ON_ONCE(!schedule_work(&user->put_work))) {
                /*
                 * If we fail we must wait for an admin to attempt delete or
                 * another register/close of the event, whichever is first.
                 */
                pr_warn("user_events: Unable to queue delayed destroy\n");
        }
out:
        /* Ensure if we didn't have event_mutex before we unlock it */
        if (!locked)
                mutex_unlock(&event_mutex);
}

static void user_event_group_destroy(struct user_event_group *group)
{
        kfree(group->system_name);
        kfree(group->system_multi_name);
        kfree(group);
}

static char *user_event_group_system_name(void)
{
        char *system_name;
        int len = sizeof(USER_EVENTS_SYSTEM) + 1;

        system_name = kmalloc(len, GFP_KERNEL);

        if (!system_name)
                return NULL;

        snprintf(system_name, len, "%s", USER_EVENTS_SYSTEM);

        return system_name;
}

static char *user_event_group_system_multi_name(void)
{
        return kstrdup(USER_EVENTS_MULTI_SYSTEM, GFP_KERNEL);
}

static struct user_event_group *current_user_event_group(void)
{
        return init_group;
}

static struct user_event_group *user_event_group_create(void)
{
        struct user_event_group *group;

        group = kzalloc_obj(*group);

        if (!group)
                return NULL;

        group->system_name = user_event_group_system_name();

        if (!group->system_name)
                goto error;

        group->system_multi_name = user_event_group_system_multi_name();

        if (!group->system_multi_name)
                goto error;

        mutex_init(&group->reg_mutex);
        hash_init(group->register_table);

        return group;
error:
        if (group)
                user_event_group_destroy(group);

        return NULL;
};

static void user_event_enabler_destroy(struct user_event_enabler *enabler,
                                       bool locked)
{
        list_del_rcu(&enabler->mm_enablers_link);

        /* No longer tracking the event via the enabler */
        user_event_put(enabler->event, locked);

        kfree(enabler);
}

static int user_event_mm_fault_in(struct user_event_mm *mm, unsigned long uaddr,
                                  int attempt)
{
        bool unlocked;
        int ret;

        /*
         * Normally this is low, ensure that it cannot be taken advantage of by
         * bad user processes to cause excessive looping.
         */
        if (attempt > 10)
                return -EFAULT;

        mmap_read_lock(mm->mm);

        /* Ensure MM has tasks, cannot use after exit_mm() */
        if (refcount_read(&mm->tasks) == 0) {
                ret = -ENOENT;
                goto out;
        }

        ret = fixup_user_fault(mm->mm, uaddr, FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE,
                               &unlocked);
out:
        mmap_read_unlock(mm->mm);

        return ret;
}

static int user_event_enabler_write(struct user_event_mm *mm,
                                    struct user_event_enabler *enabler,
                                    bool fixup_fault, int *attempt);

static void user_event_enabler_fault_fixup(struct work_struct *work)
{
        struct user_event_enabler_fault *fault = container_of(
                work, struct user_event_enabler_fault, work);
        struct user_event_enabler *enabler = fault->enabler;
        struct user_event_mm *mm = fault->mm;
        unsigned long uaddr = enabler->addr;
        int attempt = fault->attempt;
        int ret;

        ret = user_event_mm_fault_in(mm, uaddr, attempt);

        if (ret && ret != -ENOENT) {
                struct user_event *user = enabler->event;

                pr_warn("user_events: Fault for mm: 0x%p @ 0x%llx event: %s\n",
                        mm->mm, (unsigned long long)uaddr, EVENT_NAME(user));
        }

        /* Prevent state changes from racing */
        mutex_lock(&event_mutex);

        /* User asked for enabler to be removed during fault */
        if (test_bit(ENABLE_VAL_FREEING_BIT, ENABLE_BITOPS(enabler))) {
                user_event_enabler_destroy(enabler, true);
                goto out;
        }

        /*
         * If we managed to get the page, re-issue the write. We do not
         * want to get into a possible infinite loop, which is why we only
         * attempt again directly if the page came in. If we couldn't get
         * the page here, then we will try again the next time the event is
         * enabled/disabled.
         */
        clear_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler));

        if (!ret) {
                mmap_read_lock(mm->mm);
                user_event_enabler_write(mm, enabler, true, &attempt);
                mmap_read_unlock(mm->mm);
        }
out:
        mutex_unlock(&event_mutex);

        /* In all cases we no longer need the mm or fault */
        user_event_mm_put(mm);
        kmem_cache_free(fault_cache, fault);
}

static bool user_event_enabler_queue_fault(struct user_event_mm *mm,
                                           struct user_event_enabler *enabler,
                                           int attempt)
{
        struct user_event_enabler_fault *fault;

        fault = kmem_cache_zalloc(fault_cache, GFP_NOWAIT);

        if (!fault)
                return false;

        INIT_WORK(&fault->work, user_event_enabler_fault_fixup);
        fault->mm = user_event_mm_get(mm);
        fault->enabler = enabler;
        fault->attempt = attempt;

        /* Don't try to queue in again while we have a pending fault */
        set_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler));

        if (!schedule_work(&fault->work)) {
                /* Allow another attempt later */
                clear_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler));

                user_event_mm_put(mm);
                kmem_cache_free(fault_cache, fault);

                return false;
        }

        return true;
}

static int user_event_enabler_write(struct user_event_mm *mm,
                                    struct user_event_enabler *enabler,
                                    bool fixup_fault, int *attempt)
{
        unsigned long uaddr = enabler->addr;
        unsigned long *ptr;
        struct page *page;
        void *kaddr;
        int bit = ENABLE_BIT(enabler);
        int ret;

        lockdep_assert_held(&event_mutex);
        mmap_assert_locked(mm->mm);

        *attempt += 1;

        /* Ensure MM has tasks, cannot use after exit_mm() */
        if (refcount_read(&mm->tasks) == 0)
                return -ENOENT;

        if (unlikely(test_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)) ||
                     test_bit(ENABLE_VAL_FREEING_BIT, ENABLE_BITOPS(enabler))))
                return -EBUSY;

        align_addr_bit(&uaddr, &bit, ENABLE_BITOPS(enabler));

        ret = pin_user_pages_remote(mm->mm, uaddr, 1, FOLL_WRITE | FOLL_NOFAULT,
                                    &page, NULL);

        if (unlikely(ret <= 0)) {
                if (!fixup_fault)
                        return -EFAULT;

                if (!user_event_enabler_queue_fault(mm, enabler, *attempt))
                        pr_warn("user_events: Unable to queue fault handler\n");

                return -EFAULT;
        }

        kaddr = kmap_local_page(page);
        ptr = kaddr + (uaddr & ~PAGE_MASK);

        /* Update bit atomically, user tracers must be atomic as well */
        if (enabler->event && enabler->event->status)
                set_bit(bit, ptr);
        else
                clear_bit(bit, ptr);

        kunmap_local(kaddr);
        unpin_user_pages_dirty_lock(&page, 1, true);

        return 0;
}

static bool user_event_enabler_exists(struct user_event_mm *mm,
                                      unsigned long uaddr, unsigned char bit)
{
        struct user_event_enabler *enabler;

        list_for_each_entry(enabler, &mm->enablers, mm_enablers_link) {
                if (enabler->addr == uaddr && ENABLE_BIT(enabler) == bit)
                        return true;
        }

        return false;
}

static void user_event_enabler_update(struct user_event *user)
{
        struct user_event_enabler *enabler;
        struct user_event_mm *next;
        struct user_event_mm *mm;
        int attempt;

        lockdep_assert_held(&event_mutex);

        /*
         * We need to build a one-shot list of all the mms that have an
         * enabler for the user_event passed in. This list is only valid
         * while holding the event_mutex. The only reason for this is due
         * to the global mm list being RCU protected and we use methods
         * which can wait (mmap_read_lock and pin_user_pages_remote).
         *
         * NOTE: user_event_mm_get_all() increments the ref count of each
         * mm that is added to the list to prevent removal timing windows.
         * We must always put each mm after they are used, which may wait.
         */
        mm = user_event_mm_get_all(user);

        while (mm) {
                next = mm->next;
                mmap_read_lock(mm->mm);

                list_for_each_entry(enabler, &mm->enablers, mm_enablers_link) {
                        if (enabler->event == user) {
                                attempt = 0;
                                user_event_enabler_write(mm, enabler, true, &attempt);
                        }
                }

                mmap_read_unlock(mm->mm);
                user_event_mm_put(mm);
                mm = next;
        }
}

static bool user_event_enabler_dup(struct user_event_enabler *orig,
                                   struct user_event_mm *mm)
{
        struct user_event_enabler *enabler;

        /* Skip pending frees */
        if (unlikely(test_bit(ENABLE_VAL_FREEING_BIT, ENABLE_BITOPS(orig))))
                return true;

        enabler = kzalloc_obj(*enabler, GFP_NOWAIT | __GFP_ACCOUNT);

        if (!enabler)
                return false;

        enabler->event = user_event_get(orig->event);
        enabler->addr = orig->addr;

        /* Only dup part of value (ignore future flags, etc) */
        enabler->values = orig->values & ENABLE_VAL_DUP_MASK;

        /* Enablers not exposed yet, RCU not required */
        list_add(&enabler->mm_enablers_link, &mm->enablers);

        return true;
}

static struct user_event_mm *user_event_mm_get(struct user_event_mm *mm)
{
        refcount_inc(&mm->refcnt);

        return mm;
}

static struct user_event_mm *user_event_mm_get_all(struct user_event *user)
{
        struct user_event_mm *found = NULL;
        struct user_event_enabler *enabler;
        struct user_event_mm *mm;

        /*
         * We use the mm->next field to build a one-shot list from the global
         * RCU protected list. To build this list the event_mutex must be held.
         * This lets us build a list without requiring allocs that could fail
         * when user based events are most wanted for diagnostics.
         */
        lockdep_assert_held(&event_mutex);

        /*
         * We do not want to block fork/exec while enablements are being
         * updated, so we use RCU to walk the current tasks that have used
         * user_events ABI for 1 or more events. Each enabler found in each
         * task that matches the event being updated has a write to reflect
         * the kernel state back into the process. Waits/faults must not occur
         * during this. So we scan the list under RCU for all the mm that have
         * the event within it. This is needed because mm_read_lock() can wait.
         * Each user mm returned has a ref inc to handle remove RCU races.
         */
        rcu_read_lock();

        list_for_each_entry_rcu(mm, &user_event_mms, mms_link) {
                list_for_each_entry_rcu(enabler, &mm->enablers, mm_enablers_link) {
                        if (enabler->event == user) {
                                mm->next = found;
                                found = user_event_mm_get(mm);
                                break;
                        }
                }
        }

        rcu_read_unlock();

        return found;
}

static struct user_event_mm *user_event_mm_alloc(struct task_struct *t)
{
        struct user_event_mm *user_mm;

        user_mm = kzalloc_obj(*user_mm, GFP_KERNEL_ACCOUNT);

        if (!user_mm)
                return NULL;

        user_mm->mm = t->mm;
        INIT_LIST_HEAD(&user_mm->enablers);
        refcount_set(&user_mm->refcnt, 1);
        refcount_set(&user_mm->tasks, 1);

        /*
         * The lifetime of the memory descriptor can slightly outlast
         * the task lifetime if a ref to the user_event_mm is taken
         * between list_del_rcu() and call_rcu(). Therefore we need
         * to take a reference to it to ensure it can live this long
         * under this corner case. This can also occur in clones that
         * outlast the parent.
         */
        mmgrab(user_mm->mm);

        return user_mm;
}

static void user_event_mm_attach(struct user_event_mm *user_mm, struct task_struct *t)
{
        unsigned long flags;

        spin_lock_irqsave(&user_event_mms_lock, flags);
        list_add_rcu(&user_mm->mms_link, &user_event_mms);
        spin_unlock_irqrestore(&user_event_mms_lock, flags);

        t->user_event_mm = user_mm;
}

static struct user_event_mm *current_user_event_mm(void)
{
        struct user_event_mm *user_mm = current->user_event_mm;

        if (user_mm)
                goto inc;

        user_mm = user_event_mm_alloc(current);

        if (!user_mm)
                goto error;

        user_event_mm_attach(user_mm, current);
inc:
        refcount_inc(&user_mm->refcnt);
error:
        return user_mm;
}

static void user_event_mm_destroy(struct user_event_mm *mm)
{
        struct user_event_enabler *enabler, *next;

        list_for_each_entry_safe(enabler, next, &mm->enablers, mm_enablers_link)
                user_event_enabler_destroy(enabler, false);

        mmdrop(mm->mm);
        kfree(mm);
}

static void user_event_mm_put(struct user_event_mm *mm)
{
        if (mm && refcount_dec_and_test(&mm->refcnt))
                user_event_mm_destroy(mm);
}

static void delayed_user_event_mm_put(struct work_struct *work)
{
        struct user_event_mm *mm;

        mm = container_of(to_rcu_work(work), struct user_event_mm, put_rwork);
        user_event_mm_put(mm);
}

void user_event_mm_remove(struct task_struct *t)
{
        struct user_event_mm *mm;
        unsigned long flags;

        might_sleep();

        mm = t->user_event_mm;
        t->user_event_mm = NULL;

        /* Clone will increment the tasks, only remove if last clone */
        if (!refcount_dec_and_test(&mm->tasks))
                return;

        /* Remove the mm from the list, so it can no longer be enabled */
        spin_lock_irqsave(&user_event_mms_lock, flags);
        list_del_rcu(&mm->mms_link);
        spin_unlock_irqrestore(&user_event_mms_lock, flags);

        /*
         * We need to wait for currently occurring writes to stop within
         * the mm. This is required since exit_mm() snaps the current rss
         * stats and clears them. On the final mmdrop(), check_mm() will
         * report a bug if these increment.
         *
         * All writes/pins are done under mmap_read lock, take the write
         * lock to ensure in-progress faults have completed. Faults that
         * are pending but yet to run will check the task count and skip
         * the fault since the mm is going away.
         */
        mmap_write_lock(mm->mm);
        mmap_write_unlock(mm->mm);

        /*
         * Put for mm must be done after RCU delay to handle new refs in
         * between the list_del_rcu() and now. This ensures any get refs
         * during rcu_read_lock() are accounted for during list removal.
         *
         * CPU A                        |       CPU B
         * ---------------------------------------------------------------
         * user_event_mm_remove()       |       rcu_read_lock();
         * list_del_rcu()               |       list_for_each_entry_rcu();
         * call_rcu()                   |       refcount_inc();
         * .                            |       rcu_read_unlock();
         * schedule_work()              |       .
         * user_event_mm_put()          |       .
         *
         * mmdrop() cannot be called in the softirq context of call_rcu()
         * so we use a work queue after call_rcu() to run within.
         */
        INIT_RCU_WORK(&mm->put_rwork, delayed_user_event_mm_put);
        queue_rcu_work(system_percpu_wq, &mm->put_rwork);
}

void user_event_mm_dup(struct task_struct *t, struct user_event_mm *old_mm)
{
        struct user_event_mm *mm = user_event_mm_alloc(t);
        struct user_event_enabler *enabler;

        if (!mm)
                return;

        rcu_read_lock();

        list_for_each_entry_rcu(enabler, &old_mm->enablers, mm_enablers_link) {
                if (!user_event_enabler_dup(enabler, mm))
                        goto error;
        }

        rcu_read_unlock();

        user_event_mm_attach(mm, t);
        return;
error:
        rcu_read_unlock();
        user_event_mm_destroy(mm);
}

static bool current_user_event_enabler_exists(unsigned long uaddr,
                                              unsigned char bit)
{
        struct user_event_mm *user_mm = current_user_event_mm();
        bool exists;

        if (!user_mm)
                return false;

        exists = user_event_enabler_exists(user_mm, uaddr, bit);

        user_event_mm_put(user_mm);

        return exists;
}

static struct user_event_enabler
*user_event_enabler_create(struct user_reg *reg, struct user_event *user,
                           int *write_result)
{
        struct user_event_enabler *enabler;
        struct user_event_mm *user_mm;
        unsigned long uaddr = (unsigned long)reg->enable_addr;
        int attempt = 0;

        user_mm = current_user_event_mm();

        if (!user_mm)
                return NULL;

        enabler = kzalloc_obj(*enabler, GFP_KERNEL_ACCOUNT);

        if (!enabler)
                goto out;

        enabler->event = user;
        enabler->addr = uaddr;
        enabler->values = reg->enable_bit;

#if BITS_PER_LONG >= 64
        if (reg->enable_size == 4)
                set_bit(ENABLE_VAL_32_ON_64_BIT, ENABLE_BITOPS(enabler));
#endif

retry:
        /* Prevents state changes from racing with new enablers */
        mutex_lock(&event_mutex);

        /* Attempt to reflect the current state within the process */
        mmap_read_lock(user_mm->mm);
        *write_result = user_event_enabler_write(user_mm, enabler, false,
                                                 &attempt);
        mmap_read_unlock(user_mm->mm);

        /*
         * If the write works, then we will track the enabler. A ref to the
         * underlying user_event is held by the enabler to prevent it going
         * away while the enabler is still in use by a process. The ref is
         * removed when the enabler is destroyed. This means a event cannot
         * be forcefully deleted from the system until all tasks using it
         * exit or run exec(), which includes forks and clones.
         */
        if (!*write_result) {
                user_event_get(user);
                list_add_rcu(&enabler->mm_enablers_link, &user_mm->enablers);
        }

        mutex_unlock(&event_mutex);

        if (*write_result) {
                /* Attempt to fault-in and retry if it worked */
                if (!user_event_mm_fault_in(user_mm, uaddr, attempt))
                        goto retry;

                kfree(enabler);
                enabler = NULL;
        }
out:
        user_event_mm_put(user_mm);

        return enabler;
}

static __always_inline __must_check
bool user_event_last_ref(struct user_event *user)
{
        int last = 0;

        if (user->reg_flags & USER_EVENT_REG_PERSIST)
                last = 1;

        return refcount_read(&user->refcnt) == last;
}

static __always_inline __must_check
size_t copy_nofault(void *addr, size_t bytes, struct iov_iter *i)
{
        size_t ret;

        pagefault_disable();

        ret = copy_from_iter_nocache(addr, bytes, i);

        pagefault_enable();

        return ret;
}

static struct list_head *user_event_get_fields(struct trace_event_call *call)
{
        struct user_event *user = (struct user_event *)call->data;

        return &user->fields;
}

/*
 * Parses a register command for user_events
 * Format: event_name[:FLAG1[,FLAG2...]] [field1[;field2...]]
 *
 * Example event named 'test' with a 20 char 'msg' field with an unsigned int
 * 'id' field after:
 * test char[20] msg;unsigned int id
 *
 * NOTE: Offsets are from the user data perspective, they are not from the
 * trace_entry/buffer perspective. We automatically add the common properties
 * sizes to the offset for the user.
 *
 * Upon success user_event has its ref count increased by 1.
 */
static int user_event_parse_cmd(struct user_event_group *group,
                                char *raw_command, struct user_event **newuser,
                                int reg_flags)
{
        char *name = raw_command;
        char *args = strpbrk(name, " ");
        char *flags;

        if (args)
                *args++ = '\0';

        flags = strpbrk(name, ":");

        if (flags)
                *flags++ = '\0';

        return user_event_parse(group, name, args, flags, newuser, reg_flags);
}

static int user_field_array_size(const char *type)
{
        const char *start = strchr(type, '[');
        char val[8];
        char *bracket;
        int size = 0;

        if (start == NULL)
                return -EINVAL;

        if (strscpy(val, start + 1, sizeof(val)) <= 0)
                return -EINVAL;

        bracket = strchr(val, ']');

        if (!bracket)
                return -EINVAL;

        *bracket = '\0';

        if (kstrtouint(val, 0, &size))
                return -EINVAL;

        if (size > MAX_FIELD_ARRAY_SIZE)
                return -EINVAL;

        return size;
}

static int user_field_size(const char *type)
{
        /* long is not allowed from a user, since it's ambiguous in size */
        if (strcmp(type, "s64") == 0)
                return sizeof(s64);
        if (strcmp(type, "u64") == 0)
                return sizeof(u64);
        if (strcmp(type, "s32") == 0)
                return sizeof(s32);
        if (strcmp(type, "u32") == 0)
                return sizeof(u32);
        if (strcmp(type, "int") == 0)
                return sizeof(int);
        if (strcmp(type, "unsigned int") == 0)
                return sizeof(unsigned int);
        if (strcmp(type, "s16") == 0)
                return sizeof(s16);
        if (strcmp(type, "u16") == 0)
                return sizeof(u16);
        if (strcmp(type, "short") == 0)
                return sizeof(short);
        if (strcmp(type, "unsigned short") == 0)
                return sizeof(unsigned short);
        if (strcmp(type, "s8") == 0)
                return sizeof(s8);
        if (strcmp(type, "u8") == 0)
                return sizeof(u8);
        if (strcmp(type, "char") == 0)
                return sizeof(char);
        if (strcmp(type, "unsigned char") == 0)
                return sizeof(unsigned char);
        if (str_has_prefix(type, "char["))
                return user_field_array_size(type);
        if (str_has_prefix(type, "unsigned char["))
                return user_field_array_size(type);
        if (str_has_prefix(type, "__data_loc "))
                return sizeof(u32);
        if (str_has_prefix(type, "__rel_loc "))
                return sizeof(u32);

        /* Unknown basic type, error */
        return -EINVAL;
}

static void user_event_destroy_validators(struct user_event *user)
{
        struct user_event_validator *validator, *next;
        struct list_head *head = &user->validators;

        list_for_each_entry_safe(validator, next, head, user_event_link) {
                list_del(&validator->user_event_link);
                kfree(validator);
        }
}

static void user_event_destroy_fields(struct user_event *user)
{
        struct ftrace_event_field *field, *next;
        struct list_head *head = &user->fields;

        list_for_each_entry_safe(field, next, head, link) {
                list_del(&field->link);
                kfree(field);
        }
}

static int user_event_add_field(struct user_event *user, const char *type,
                                const char *name, int offset, int size,
                                int is_signed, int filter_type)
{
        struct user_event_validator *validator;
        struct ftrace_event_field *field;
        int validator_flags = 0;

        field = kmalloc_obj(*field, GFP_KERNEL_ACCOUNT);

        if (!field)
                return -ENOMEM;

        if (str_has_prefix(type, "__data_loc "))
                goto add_validator;

        if (str_has_prefix(type, "__rel_loc ")) {
                validator_flags |= VALIDATOR_REL;
                goto add_validator;
        }

        goto add_field;

add_validator:
        if (strstr(type, "char") != NULL)
                validator_flags |= VALIDATOR_ENSURE_NULL;

        validator = kmalloc_obj(*validator, GFP_KERNEL_ACCOUNT);

        if (!validator) {
                kfree(field);
                return -ENOMEM;
        }

        validator->flags = validator_flags;
        validator->offset = offset;

        /* Want sequential access when validating */
        list_add_tail(&validator->user_event_link, &user->validators);

add_field:
        field->type = type;
        field->name = name;
        field->offset = offset;
        field->size = size;
        field->is_signed = is_signed;
        field->filter_type = filter_type;

        if (filter_type == FILTER_OTHER)
                field->filter_type = filter_assign_type(type);

        list_add(&field->link, &user->fields);

        /*
         * Min size from user writes that are required, this does not include
         * the size of trace_entry (common fields).
         */
        user->min_size = (offset + size) - sizeof(struct trace_entry);

        return 0;
}

/*
 * Parses the values of a field within the description
 * Format: type name [size]
 */
static int user_event_parse_field(char *field, struct user_event *user,
                                  u32 *offset)
{
        char *part, *type, *name;
        u32 depth = 0, saved_offset = *offset;
        int len, size = -EINVAL;
        bool is_struct = false;

        field = skip_spaces(field);

        if (*field == '\0')
                return 0;

        /* Handle types that have a space within */
        len = str_has_prefix(field, "unsigned ");
        if (len)
                goto skip_next;

        len = str_has_prefix(field, "struct ");
        if (len) {
                is_struct = true;
                goto skip_next;
        }

        len = str_has_prefix(field, "__data_loc unsigned ");
        if (len)
                goto skip_next;

        len = str_has_prefix(field, "__data_loc ");
        if (len)
                goto skip_next;

        len = str_has_prefix(field, "__rel_loc unsigned ");
        if (len)
                goto skip_next;

        len = str_has_prefix(field, "__rel_loc ");
        if (len)
                goto skip_next;

        goto parse;
skip_next:
        type = field;
        field = strpbrk(field + len, " ");

        if (field == NULL)
                return -EINVAL;

        *field++ = '\0';
        depth++;
parse:
        name = NULL;

        while ((part = strsep(&field, " ")) != NULL) {
                switch (depth++) {
                case FIELD_DEPTH_TYPE:
                        type = part;
                        break;
                case FIELD_DEPTH_NAME:
                        name = part;
                        break;
                case FIELD_DEPTH_SIZE:
                        if (!is_struct)
                                return -EINVAL;

                        if (kstrtou32(part, 10, &size))
                                return -EINVAL;
                        break;
                default:
                        return -EINVAL;
                }
        }

        if (depth < FIELD_DEPTH_SIZE || !name)
                return -EINVAL;

        if (depth == FIELD_DEPTH_SIZE)
                size = user_field_size(type);

        if (size == 0)
                return -EINVAL;

        if (size < 0)
                return size;

        *offset = saved_offset + size;

        return user_event_add_field(user, type, name, saved_offset, size,
                                    type[0] != 'u', FILTER_OTHER);
}

static int user_event_parse_fields(struct user_event *user, char *args)
{
        char *field;
        u32 offset = sizeof(struct trace_entry);
        int ret = -EINVAL;

        if (args == NULL)
                return 0;

        while ((field = strsep(&args, ";")) != NULL) {
                ret = user_event_parse_field(field, user, &offset);

                if (ret)
                        break;
        }

        return ret;
}

static struct trace_event_fields user_event_fields_array[1];

static const char *user_field_format(const char *type)
{
        if (strcmp(type, "s64") == 0)
                return "%lld";
        if (strcmp(type, "u64") == 0)
                return "%llu";
        if (strcmp(type, "s32") == 0)
                return "%d";
        if (strcmp(type, "u32") == 0)
                return "%u";
        if (strcmp(type, "int") == 0)
                return "%d";
        if (strcmp(type, "unsigned int") == 0)
                return "%u";
        if (strcmp(type, "s16") == 0)
                return "%d";
        if (strcmp(type, "u16") == 0)
                return "%u";
        if (strcmp(type, "short") == 0)
                return "%d";
        if (strcmp(type, "unsigned short") == 0)
                return "%u";
        if (strcmp(type, "s8") == 0)
                return "%d";
        if (strcmp(type, "u8") == 0)
                return "%u";
        if (strcmp(type, "char") == 0)
                return "%d";
        if (strcmp(type, "unsigned char") == 0)
                return "%u";
        if (strstr(type, "char[") != NULL)
                return "%s";

        /* Unknown, likely struct, allowed treat as 64-bit */
        return "%llu";
}

static bool user_field_is_dyn_string(const char *type, const char **str_func)
{
        if (str_has_prefix(type, "__data_loc ")) {
                *str_func = "__get_str";
                goto check;
        }

        if (str_has_prefix(type, "__rel_loc ")) {
                *str_func = "__get_rel_str";
                goto check;
        }

        return false;
check:
        return strstr(type, "char") != NULL;
}

#define LEN_OR_ZERO (len ? len - pos : 0)
static int user_dyn_field_set_string(int argc, const char **argv, int *iout,
                                     char *buf, int len, bool *colon)
{
        int pos = 0, i = *iout;

        *colon = false;

        for (; i < argc; ++i) {
                if (i != *iout)
                        pos += snprintf(buf + pos, LEN_OR_ZERO, " ");

                pos += snprintf(buf + pos, LEN_OR_ZERO, "%s", argv[i]);

                if (strchr(argv[i], ';')) {
                        ++i;
                        *colon = true;
                        break;
                }
        }

        /* Actual set, advance i */
        if (len != 0)
                *iout = i;

        return pos + 1;
}

static int user_field_set_string(struct ftrace_event_field *field,
                                 char *buf, int len, bool colon)
{
        int pos = 0;

        pos += snprintf(buf + pos, LEN_OR_ZERO, "%s", field->type);
        pos += snprintf(buf + pos, LEN_OR_ZERO, " ");
        pos += snprintf(buf + pos, LEN_OR_ZERO, "%s", field->name);

        if (str_has_prefix(field->type, "struct "))
                pos += snprintf(buf + pos, LEN_OR_ZERO, " %d", field->size);

        if (colon)
                pos += snprintf(buf + pos, LEN_OR_ZERO, ";");

        return pos + 1;
}

static int user_event_set_print_fmt(struct user_event *user, char *buf, int len)
{
        struct ftrace_event_field *field;
        struct list_head *head = &user->fields;
        int pos = 0, depth = 0;
        const char *str_func;

        pos += snprintf(buf + pos, LEN_OR_ZERO, "\"");

        list_for_each_entry_reverse(field, head, link) {
                if (depth != 0)
                        pos += snprintf(buf + pos, LEN_OR_ZERO, " ");

                pos += snprintf(buf + pos, LEN_OR_ZERO, "%s=%s",
                                field->name, user_field_format(field->type));

                depth++;
        }

        pos += snprintf(buf + pos, LEN_OR_ZERO, "\"");

        list_for_each_entry_reverse(field, head, link) {
                if (user_field_is_dyn_string(field->type, &str_func))
                        pos += snprintf(buf + pos, LEN_OR_ZERO,
                                        ", %s(%s)", str_func, field->name);
                else
                        pos += snprintf(buf + pos, LEN_OR_ZERO,
                                        ", REC->%s", field->name);
        }

        return pos + 1;
}
#undef LEN_OR_ZERO

static int user_event_create_print_fmt(struct user_event *user)
{
        char *print_fmt;
        int len;

        len = user_event_set_print_fmt(user, NULL, 0);

        print_fmt = kmalloc(len, GFP_KERNEL_ACCOUNT);

        if (!print_fmt)
                return -ENOMEM;

        user_event_set_print_fmt(user, print_fmt, len);

        user->call.print_fmt = print_fmt;

        return 0;
}

static enum print_line_t user_event_print_trace(struct trace_iterator *iter,
                                                int flags,
                                                struct trace_event *event)
{
        return print_event_fields(iter, event);
}

static struct trace_event_functions user_event_funcs = {
        .trace = user_event_print_trace,
};

static int user_event_set_call_visible(struct user_event *user, bool visible)
{
        CLASS(prepare_creds, cred)();
        if (!cred)
                return -ENOMEM;

        /*
         * While by default tracefs is locked down, systems can be configured
         * to allow user_event files to be less locked down. The extreme case
         * being "other" has read/write access to user_events_data/status.
         *
         * When not locked down, processes may not have permissions to
         * add/remove calls themselves to tracefs. We need to temporarily
         * switch to root file permission to allow for this scenario.
         */
        cred->fsuid = GLOBAL_ROOT_UID;

        scoped_with_creds(cred) {
                if (visible)
                        return trace_add_event_call(&user->call);

                return trace_remove_event_call(&user->call);
        }
}

static int destroy_user_event(struct user_event *user)
{
        int ret = 0;

        lockdep_assert_held(&event_mutex);

        /* Must destroy fields before call removal */
        user_event_destroy_fields(user);

        ret = user_event_set_call_visible(user, false);

        if (ret)
                return ret;

        dyn_event_remove(&user->devent);
        hash_del(&user->node);

        user_event_destroy_validators(user);

        /* If we have different names, both must be freed */
        if (EVENT_NAME(user) != EVENT_TP_NAME(user))
                kfree(EVENT_TP_NAME(user));

        kfree(user->call.print_fmt);
        kfree(EVENT_NAME(user));
        kfree(user);

        if (current_user_events > 0)
                current_user_events--;
        else
                pr_alert("BUG: Bad current_user_events\n");

        return ret;
}

static struct user_event *find_user_event(struct user_event_group *group,
                                          char *name, int argc, const char **argv,
                                          u32 flags, u32 *outkey)
{
        struct user_event *user;
        u32 key = user_event_key(name);

        *outkey = key;

        hash_for_each_possible(group->register_table, user, node, key) {
                /*
                 * Single-format events shouldn't return multi-format
                 * events. Callers expect the underlying tracepoint to match
                 * the name exactly in these cases. Only check like-formats.
                 */
                if (EVENT_MULTI_FORMAT(flags) != EVENT_MULTI_FORMAT(user->reg_flags))
                        continue;

                if (strcmp(EVENT_NAME(user), name))
                        continue;

                if (user_fields_match(user, argc, argv))
                        return user_event_get(user);

                /* Scan others if this is a multi-format event */
                if (EVENT_MULTI_FORMAT(flags))
                        continue;

                return ERR_PTR(-EADDRINUSE);
        }

        return NULL;
}

static int user_event_validate(struct user_event *user, void *data, int len)
{
        struct list_head *head = &user->validators;
        struct user_event_validator *validator;
        void *pos, *end = data + len;
        u32 loc, offset, size;

        list_for_each_entry(validator, head, user_event_link) {
                pos = data + validator->offset;

                /* Already done min_size check, no bounds check here */
                loc = *(u32 *)pos;
                offset = loc & 0xffff;
                size = loc >> 16;

                if (likely(validator->flags & VALIDATOR_REL))
                        pos += offset + sizeof(loc);
                else
                        pos = data + offset;

                pos += size;

                if (unlikely(pos > end))
                        return -EFAULT;

                if (likely(validator->flags & VALIDATOR_ENSURE_NULL))
                        if (unlikely(*(char *)(pos - 1) != '\0'))
                                return -EFAULT;
        }

        return 0;
}

/*
 * Writes the user supplied payload out to a trace file.
 */
static void user_event_ftrace(struct user_event *user, struct iov_iter *i,
                              void *tpdata, bool *faulted)
{
        struct trace_event_file *file;
        struct trace_entry *entry;
        struct trace_event_buffer event_buffer;
        size_t size = sizeof(*entry) + i->count;

        file = (struct trace_event_file *)tpdata;

        if (!file ||
            !(file->flags & EVENT_FILE_FL_ENABLED) ||
            trace_trigger_soft_disabled(file))
                return;

        /* Allocates and fills trace_entry, + 1 of this is data payload */
        entry = trace_event_buffer_reserve(&event_buffer, file, size);

        if (unlikely(!entry))
                return;

        if (unlikely(i->count != 0 && !copy_nofault(entry + 1, i->count, i)))
                goto discard;

        if (!list_empty(&user->validators) &&
            unlikely(user_event_validate(user, entry, size)))
                goto discard;

        trace_event_buffer_commit(&event_buffer);

        return;
discard:
        *faulted = true;
        __trace_event_discard_commit(event_buffer.buffer,
                                     event_buffer.event);
}

#ifdef CONFIG_PERF_EVENTS
/*
 * Writes the user supplied payload out to perf ring buffer.
 */
static void user_event_perf(struct user_event *user, struct iov_iter *i,
                            void *tpdata, bool *faulted)
{
        struct hlist_head *perf_head;

        perf_head = this_cpu_ptr(user->call.perf_events);

        if (perf_head && !hlist_empty(perf_head)) {
                struct trace_entry *perf_entry;
                struct pt_regs *regs;
                size_t size = sizeof(*perf_entry) + i->count;
                int context;

                perf_entry = perf_trace_buf_alloc(ALIGN(size, 8),
                                                  &regs, &context);

                if (unlikely(!perf_entry))
                        return;

                perf_fetch_caller_regs(regs);

                if (unlikely(i->count != 0 && !copy_nofault(perf_entry + 1, i->count, i)))
                        goto discard;

                if (!list_empty(&user->validators) &&
                    unlikely(user_event_validate(user, perf_entry, size)))
                        goto discard;

                perf_trace_buf_submit(perf_entry, size, context,
                                      user->call.event.type, 1, regs,
                                      perf_head, NULL);

                return;
discard:
                *faulted = true;
                perf_swevent_put_recursion_context(context);
        }
}
#endif

/*
 * Update the enabled bit among all user processes.
 */
static void update_enable_bit_for(struct user_event *user)
{
        struct tracepoint *tp = &user->tracepoint;
        char status = 0;

        if (static_key_enabled(&tp->key)) {
                struct tracepoint_func *probe_func_ptr;
                user_event_func_t probe_func;

                rcu_read_lock_sched();

                probe_func_ptr = rcu_dereference_sched(tp->funcs);

                if (probe_func_ptr) {
                        do {
                                probe_func = probe_func_ptr->func;

                                if (probe_func == user_event_ftrace)
                                        status |= EVENT_STATUS_FTRACE;
#ifdef CONFIG_PERF_EVENTS
                                else if (probe_func == user_event_perf)
                                        status |= EVENT_STATUS_PERF;
#endif
                                else
                                        status |= EVENT_STATUS_OTHER;
                        } while ((++probe_func_ptr)->func);
                }

                rcu_read_unlock_sched();
        }

        user->status = status;

        user_event_enabler_update(user);
}

/*
 * Register callback for our events from tracing sub-systems.
 */
static int user_event_reg(struct trace_event_call *call,
                          enum trace_reg type,
                          void *data)
{
        struct user_event *user = (struct user_event *)call->data;
        int ret = 0;

        if (!user)
                return -ENOENT;

        switch (type) {
        case TRACE_REG_REGISTER:
                ret = tracepoint_probe_register(call->tp,
                                                call->class->probe,
                                                data);
                if (!ret)
                        goto inc;
                break;

        case TRACE_REG_UNREGISTER:
                tracepoint_probe_unregister(call->tp,
                                            call->class->probe,
                                            data);
                goto dec;

#ifdef CONFIG_PERF_EVENTS
        case TRACE_REG_PERF_REGISTER:
                ret = tracepoint_probe_register(call->tp,
                                                call->class->perf_probe,
                                                data);
                if (!ret)
                        goto inc;
                break;

        case TRACE_REG_PERF_UNREGISTER:
                tracepoint_probe_unregister(call->tp,
                                            call->class->perf_probe,
                                            data);
                goto dec;

        case TRACE_REG_PERF_OPEN:
        case TRACE_REG_PERF_CLOSE:
        case TRACE_REG_PERF_ADD:
        case TRACE_REG_PERF_DEL:
                break;
#endif
        }

        return ret;
inc:
        user_event_get(user);
        update_enable_bit_for(user);
        return 0;
dec:
        update_enable_bit_for(user);
        user_event_put(user, true);
        return 0;
}

static int user_event_create(const char *raw_command)
{
        struct user_event_group *group;
        struct user_event *user;
        char *name;
        int ret;

        if (!str_has_prefix(raw_command, USER_EVENTS_PREFIX))
                return -ECANCELED;

        raw_command += USER_EVENTS_PREFIX_LEN;
        raw_command = skip_spaces(raw_command);

        name = kstrdup(raw_command, GFP_KERNEL_ACCOUNT);

        if (!name)
                return -ENOMEM;

        group = current_user_event_group();

        if (!group) {
                kfree(name);
                return -ENOENT;
        }

        mutex_lock(&group->reg_mutex);

        /* Dyn events persist, otherwise they would cleanup immediately */
        ret = user_event_parse_cmd(group, name, &user, USER_EVENT_REG_PERSIST);

        if (!ret)
                user_event_put(user, false);

        mutex_unlock(&group->reg_mutex);

        if (ret)
                kfree(name);

        return ret;
}

static int user_event_show(struct seq_file *m, struct dyn_event *ev)
{
        struct user_event *user = container_of(ev, struct user_event, devent);
        struct ftrace_event_field *field;
        struct list_head *head;
        int depth = 0;

        seq_printf(m, "%s%s", USER_EVENTS_PREFIX, EVENT_NAME(user));

        head = trace_get_fields(&user->call);

        list_for_each_entry_reverse(field, head, link) {
                if (depth == 0)
                        seq_puts(m, " ");
                else
                        seq_puts(m, "; ");

                seq_printf(m, "%s %s", field->type, field->name);

                if (str_has_prefix(field->type, "struct "))
                        seq_printf(m, " %d", field->size);

                depth++;
        }

        seq_puts(m, "\n");

        return 0;
}

static bool user_event_is_busy(struct dyn_event *ev)
{
        struct user_event *user = container_of(ev, struct user_event, devent);

        return !user_event_last_ref(user);
}

static int user_event_free(struct dyn_event *ev)
{
        struct user_event *user = container_of(ev, struct user_event, devent);

        if (!user_event_last_ref(user))
                return -EBUSY;

        if (!user_event_capable(user->reg_flags))
                return -EPERM;

        return destroy_user_event(user);
}

static bool user_field_match(struct ftrace_event_field *field, int argc,
                             const char **argv, int *iout)
{
        char *field_name = NULL, *dyn_field_name = NULL;
        bool colon = false, match = false;
        int dyn_len, len;

        if (*iout >= argc)
                return false;

        dyn_len = user_dyn_field_set_string(argc, argv, iout, dyn_field_name,
                                            0, &colon);

        len = user_field_set_string(field, field_name, 0, colon);

        if (dyn_len != len)
                return false;

        dyn_field_name = kmalloc(dyn_len, GFP_KERNEL);
        field_name = kmalloc(len, GFP_KERNEL);

        if (!dyn_field_name || !field_name)
                goto out;

        user_dyn_field_set_string(argc, argv, iout, dyn_field_name,
                                  dyn_len, &colon);

        user_field_set_string(field, field_name, len, colon);

        match = strcmp(dyn_field_name, field_name) == 0;
out:
        kfree(dyn_field_name);
        kfree(field_name);

        return match;
}

static bool user_fields_match(struct user_event *user, int argc,
                              const char **argv)
{
        struct ftrace_event_field *field;
        struct list_head *head = &user->fields;
        int i = 0;

        if (argc == 0)
                return list_empty(head);

        list_for_each_entry_reverse(field, head, link) {
                if (!user_field_match(field, argc, argv, &i))
                        return false;
        }

        if (i != argc)
                return false;

        return true;
}

static bool user_event_match(const char *system, const char *event,
                             int argc, const char **argv, struct dyn_event *ev)
{
        struct user_event *user = container_of(ev, struct user_event, devent);
        bool match;

        match = strcmp(EVENT_NAME(user), event) == 0;

        if (match && system) {
                match = strcmp(system, user->group->system_name) == 0 ||
                        strcmp(system, user->group->system_multi_name) == 0;
        }

        if (match)
                match = user_fields_match(user, argc, argv);

        return match;
}

static struct dyn_event_operations user_event_dops = {
        .create = user_event_create,
        .show = user_event_show,
        .is_busy = user_event_is_busy,
        .free = user_event_free,
        .match = user_event_match,
};

static int user_event_trace_register(struct user_event *user)
{
        int ret;

        ret = register_trace_event(&user->call.event);

        if (!ret)
                return -ENODEV;

        ret = user_event_set_call_visible(user, true);

        if (ret)
                unregister_trace_event(&user->call.event);

        return ret;
}

static int user_event_set_tp_name(struct user_event *user)
{
        lockdep_assert_held(&user->group->reg_mutex);

        if (EVENT_MULTI_FORMAT(user->reg_flags)) {
                char *multi_name;

                multi_name = kasprintf(GFP_KERNEL_ACCOUNT, "%s.%llx",
                                       user->reg_name, user->group->multi_id);

                if (!multi_name)
                        return -ENOMEM;

                user->call.name = multi_name;
                user->tracepoint.name = multi_name;

                /* Inc to ensure unique multi-event name next time */
                user->group->multi_id++;
        } else {
                /* Non Multi-format uses register name */
                user->call.name = user->reg_name;
                user->tracepoint.name = user->reg_name;
        }

        return 0;
}

/*
 * Counts how many ';' without a trailing space are in the args.
 */
static int count_semis_no_space(char *args)
{
        int count = 0;

        while ((args = strchr(args, ';'))) {
                args++;

                if (!isspace(*args))
                        count++;
        }

        return count;
}

/*
 * Copies the arguments while ensuring all ';' have a trailing space.
 */
static char *insert_space_after_semis(char *args, int count)
{
        char *fixed, *pos;
        int len;

        len = strlen(args) + count;
        fixed = kmalloc(len + 1, GFP_KERNEL);

        if (!fixed)
                return NULL;

        pos = fixed;

        /* Insert a space after ';' if there is no trailing space. */
        while (*args) {
                *pos = *args++;

                if (*pos++ == ';' && !isspace(*args))
                        *pos++ = ' ';
        }

        *pos = '\0';

        return fixed;
}

static char **user_event_argv_split(char *args, int *argc)
{
        char **split;
        char *fixed;
        int count;

        /* Count how many ';' without a trailing space */
        count = count_semis_no_space(args);

        /* No fixup is required */
        if (!count)
                return argv_split(GFP_KERNEL, args, argc);

        /* We must fixup 'field;field' to 'field; field' */
        fixed = insert_space_after_semis(args, count);

        if (!fixed)
                return NULL;

        /* We do a normal split afterwards */
        split = argv_split(GFP_KERNEL, fixed, argc);

        /* We can free since argv_split makes a copy */
        kfree(fixed);

        return split;
}

/*
 * Parses the event name, arguments and flags then registers if successful.
 * The name buffer lifetime is owned by this method for success cases only.
 * Upon success the returned user_event has its ref count increased by 1.
 */
static int user_event_parse(struct user_event_group *group, char *name,
                            char *args, char *flags,
                            struct user_event **newuser, int reg_flags)
{
        struct user_event *user;
        char **argv = NULL;
        int argc = 0;
        int ret;
        u32 key;

        /* Currently don't support any text based flags */
        if (flags != NULL)
                return -EINVAL;

        if (!user_event_capable(reg_flags))
                return -EPERM;

        if (args) {
                argv = user_event_argv_split(args, &argc);

                if (!argv)
                        return -ENOMEM;
        }

        /* Prevent dyn_event from racing */
        mutex_lock(&event_mutex);
        user = find_user_event(group, name, argc, (const char **)argv,
                               reg_flags, &key);
        mutex_unlock(&event_mutex);

        if (argv)
                argv_free(argv);

        if (IS_ERR(user))
                return PTR_ERR(user);

        if (user) {
                *newuser = user;
                /*
                 * Name is allocated by caller, free it since it already exists.
                 * Caller only worries about failure cases for freeing.
                 */
                kfree(name);

                return 0;
        }

        user = kzalloc_obj(*user, GFP_KERNEL_ACCOUNT);

        if (!user)
                return -ENOMEM;

        INIT_LIST_HEAD(&user->class.fields);
        INIT_LIST_HEAD(&user->fields);
        INIT_LIST_HEAD(&user->validators);

        user->group = group;
        user->reg_name = name;
        user->reg_flags = reg_flags;

        ret = user_event_set_tp_name(user);

        if (ret)
                goto put_user;

        ret = user_event_parse_fields(user, args);

        if (ret)
                goto put_user;

        ret = user_event_create_print_fmt(user);

        if (ret)
                goto put_user;

        user->call.data = user;
        user->call.class = &user->class;
        user->call.flags = TRACE_EVENT_FL_TRACEPOINT;
        user->call.tp = &user->tracepoint;
        user->call.event.funcs = &user_event_funcs;

        if (EVENT_MULTI_FORMAT(user->reg_flags))
                user->class.system = group->system_multi_name;
        else
                user->class.system = group->system_name;

        user->class.fields_array = user_event_fields_array;
        user->class.get_fields = user_event_get_fields;
        user->class.reg = user_event_reg;
        user->class.probe = user_event_ftrace;
#ifdef CONFIG_PERF_EVENTS
        user->class.perf_probe = user_event_perf;
#endif

        mutex_lock(&event_mutex);

        if (current_user_events >= max_user_events) {
                ret = -EMFILE;
                goto put_user_lock;
        }

        ret = user_event_trace_register(user);

        if (ret)
                goto put_user_lock;

        if (user->reg_flags & USER_EVENT_REG_PERSIST) {
                /* Ensure we track self ref and caller ref (2) */
                refcount_set(&user->refcnt, 2);
        } else {
                /* Ensure we track only caller ref (1) */
                refcount_set(&user->refcnt, 1);
        }

        dyn_event_init(&user->devent, &user_event_dops);
        dyn_event_add(&user->devent, &user->call);
        hash_add(group->register_table, &user->node, key);
        current_user_events++;

        mutex_unlock(&event_mutex);

        *newuser = user;
        return 0;
put_user_lock:
        mutex_unlock(&event_mutex);
put_user:
        user_event_destroy_fields(user);
        user_event_destroy_validators(user);
        kfree(user->call.print_fmt);

        /* Caller frees reg_name on error, but not multi-name */
        if (EVENT_NAME(user) != EVENT_TP_NAME(user))
                kfree(EVENT_TP_NAME(user));

        kfree(user);
        return ret;
}

/*
 * Deletes previously created events if they are no longer being used.
 */
static int delete_user_event(struct user_event_group *group, char *name)
{
        struct user_event *user;
        struct hlist_node *tmp;
        u32 key = user_event_key(name);
        int ret = -ENOENT;

        /* Attempt to delete all event(s) with the name passed in */
        hash_for_each_possible_safe(group->register_table, user, tmp, node, key) {
                if (strcmp(EVENT_NAME(user), name))
                        continue;

                if (!user_event_last_ref(user))
                        return -EBUSY;

                if (!user_event_capable(user->reg_flags))
                        return -EPERM;

                ret = destroy_user_event(user);

                if (ret)
                        goto out;
        }
out:
        return ret;
}

/*
 * Validates the user payload and writes via iterator.
 */
static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
{
        struct user_event_file_info *info = file->private_data;
        struct user_event_refs *refs;
        struct user_event *user = NULL;
        struct tracepoint *tp;
        ssize_t ret = i->count;
        int idx;

        if (unlikely(copy_from_iter(&idx, sizeof(idx), i) != sizeof(idx)))
                return -EFAULT;

        if (idx < 0)
                return -EINVAL;

        rcu_read_lock_sched();

        refs = rcu_dereference_sched(info->refs);

        /*
         * The refs->events array is protected by RCU, and new items may be
         * added. But the user retrieved from indexing into the events array
         * shall be immutable while the file is opened.
         */
        if (likely(refs && idx < refs->count))
                user = refs->events[idx];

        rcu_read_unlock_sched();

        if (unlikely(user == NULL))
                return -ENOENT;

        if (unlikely(i->count < user->min_size))
                return -EINVAL;

        tp = &user->tracepoint;

        /*
         * It's possible key.enabled disables after this check, however
         * we don't mind if a few events are included in this condition.
         */
        if (likely(static_key_enabled(&tp->key))) {
                struct tracepoint_func *probe_func_ptr;
                user_event_func_t probe_func;
                struct iov_iter copy;
                void *tpdata;
                bool faulted;

                if (unlikely(fault_in_iov_iter_readable(i, i->count)))
                        return -EFAULT;

                faulted = false;

                rcu_read_lock_sched();

                probe_func_ptr = rcu_dereference_sched(tp->funcs);

                if (probe_func_ptr) {
                        do {
                                copy = *i;
                                probe_func = probe_func_ptr->func;
                                tpdata = probe_func_ptr->data;
                                probe_func(user, &copy, tpdata, &faulted);
                        } while ((++probe_func_ptr)->func);
                }

                rcu_read_unlock_sched();

                if (unlikely(faulted))
                        return -EFAULT;
        } else
                return -EBADF;

        return ret;
}

static int user_events_open(struct inode *node, struct file *file)
{
        struct user_event_group *group;
        struct user_event_file_info *info;

        group = current_user_event_group();

        if (!group)
                return -ENOENT;

        info = kzalloc_obj(*info, GFP_KERNEL_ACCOUNT);

        if (!info)
                return -ENOMEM;

        info->group = group;

        file->private_data = info;

        return 0;
}

static ssize_t user_events_write(struct file *file, const char __user *ubuf,
                                 size_t count, loff_t *ppos)
{
        struct iov_iter i;

        if (unlikely(*ppos != 0))
                return -EFAULT;

        if (unlikely(import_ubuf(ITER_SOURCE, (char __user *)ubuf, count, &i)))
                return -EFAULT;

        return user_events_write_core(file, &i);
}

static ssize_t user_events_write_iter(struct kiocb *kp, struct iov_iter *i)
{
        return user_events_write_core(kp->ki_filp, i);
}

static int user_events_ref_add(struct user_event_file_info *info,
                               struct user_event *user)
{
        struct user_event_group *group = info->group;
        struct user_event_refs *refs, *new_refs;
        int i, size, count = 0;

        refs = rcu_dereference_protected(info->refs,
                                         lockdep_is_held(&group->reg_mutex));

        if (refs) {
                count = refs->count;

                for (i = 0; i < count; ++i)
                        if (refs->events[i] == user)
                                return i;
        }

        size = struct_size(refs, events, count + 1);

        new_refs = kzalloc(size, GFP_KERNEL_ACCOUNT);

        if (!new_refs)
                return -ENOMEM;

        new_refs->count = count + 1;

        for (i = 0; i < count; ++i)
                new_refs->events[i] = refs->events[i];

        new_refs->events[i] = user_event_get(user);

        rcu_assign_pointer(info->refs, new_refs);

        if (refs)
                kfree_rcu(refs, rcu);

        return i;
}

static long user_reg_get(struct user_reg __user *ureg, struct user_reg *kreg)
{
        u32 size;
        long ret;

        ret = get_user(size, &ureg->size);

        if (ret)
                return ret;

        if (size > PAGE_SIZE)
                return -E2BIG;

        if (size < offsetofend(struct user_reg, write_index))
                return -EINVAL;

        ret = copy_struct_from_user(kreg, sizeof(*kreg), ureg, size);

        if (ret)
                return ret;

        /* Ensure only valid flags */
        if (kreg->flags & ~(USER_EVENT_REG_MAX-1))
                return -EINVAL;

        /* Ensure supported size */
        switch (kreg->enable_size) {
        case 4:
                /* 32-bit */
                break;
#if BITS_PER_LONG >= 64
        case 8:
                /* 64-bit */
                break;
#endif
        default:
                return -EINVAL;
        }

        /* Ensure natural alignment */
        if (kreg->enable_addr % kreg->enable_size)
                return -EINVAL;

        /* Ensure bit range for size */
        if (kreg->enable_bit > (kreg->enable_size * BITS_PER_BYTE) - 1)
                return -EINVAL;

        /* Ensure accessible */
        if (!access_ok((const void __user *)(uintptr_t)kreg->enable_addr,
                       kreg->enable_size))
                return -EFAULT;

        kreg->size = size;

        return 0;
}

/*
 * Registers a user_event on behalf of a user process.
 */
static long user_events_ioctl_reg(struct user_event_file_info *info,
                                  unsigned long uarg)
{
        struct user_reg __user *ureg = (struct user_reg __user *)uarg;
        struct user_reg reg;
        struct user_event *user;
        struct user_event_enabler *enabler;
        char *name;
        long ret;
        int write_result;

        ret = user_reg_get(ureg, &reg);

        if (ret)
                return ret;

        /*
         * Prevent users from using the same address and bit multiple times
         * within the same mm address space. This can cause unexpected behavior
         * for user processes that is far easier to debug if this is explicitly
         * an error upon registering.
         */
        if (current_user_event_enabler_exists((unsigned long)reg.enable_addr,
                                              reg.enable_bit))
                return -EADDRINUSE;

        name = strndup_user((const char __user *)(uintptr_t)reg.name_args,
                            MAX_EVENT_DESC);

        if (IS_ERR(name)) {
                ret = PTR_ERR(name);
                return ret;
        }

        ret = user_event_parse_cmd(info->group, name, &user, reg.flags);

        if (ret) {
                kfree(name);
                return ret;
        }

        ret = user_events_ref_add(info, user);

        /* No longer need parse ref, ref_add either worked or not */
        user_event_put(user, false);

        /* Positive number is index and valid */
        if (ret < 0)
                return ret;

        /*
         * user_events_ref_add succeeded:
         * At this point we have a user_event, it's lifetime is bound by the
         * reference count, not this file. If anything fails, the user_event
         * still has a reference until the file is released. During release
         * any remaining references (from user_events_ref_add) are decremented.
         *
         * Attempt to create an enabler, which too has a lifetime tied in the
         * same way for the event. Once the task that caused the enabler to be
         * created exits or issues exec() then the enablers it has created
         * will be destroyed and the ref to the event will be decremented.
         */
        enabler = user_event_enabler_create(&reg, user, &write_result);

        if (!enabler)
                return -ENOMEM;

        /* Write failed/faulted, give error back to caller */
        if (write_result)
                return write_result;

        put_user((u32)ret, &ureg->write_index);

        return 0;
}

/*
 * Deletes a user_event on behalf of a user process.
 */
static long user_events_ioctl_del(struct user_event_file_info *info,
                                  unsigned long uarg)
{
        void __user *ubuf = (void __user *)uarg;
        char *name;
        long ret;

        name = strndup_user(ubuf, MAX_EVENT_DESC);

        if (IS_ERR(name))
                return PTR_ERR(name);

        /* event_mutex prevents dyn_event from racing */
        mutex_lock(&event_mutex);
        ret = delete_user_event(info->group, name);
        mutex_unlock(&event_mutex);

        kfree(name);

        return ret;
}

static long user_unreg_get(struct user_unreg __user *ureg,
                           struct user_unreg *kreg)
{
        u32 size;
        long ret;

        ret = get_user(size, &ureg->size);

        if (ret)
                return ret;

        if (size > PAGE_SIZE)
                return -E2BIG;

        if (size < offsetofend(struct user_unreg, disable_addr))
                return -EINVAL;

        ret = copy_struct_from_user(kreg, sizeof(*kreg), ureg, size);

        /* Ensure no reserved values, since we don't support any yet */
        if (kreg->__reserved || kreg->__reserved2)
                return -EINVAL;

        return ret;
}

static int user_event_mm_clear_bit(struct user_event_mm *user_mm,
                                   unsigned long uaddr, unsigned char bit,
                                   unsigned long flags)
{
        struct user_event_enabler enabler;
        int result;
        int attempt = 0;

        memset(&enabler, 0, sizeof(enabler));
        enabler.addr = uaddr;
        enabler.values = bit | flags;
retry:
        /* Prevents state changes from racing with new enablers */
        mutex_lock(&event_mutex);

        /* Force the bit to be cleared, since no event is attached */
        mmap_read_lock(user_mm->mm);
        result = user_event_enabler_write(user_mm, &enabler, false, &attempt);
        mmap_read_unlock(user_mm->mm);

        mutex_unlock(&event_mutex);

        if (result) {
                /* Attempt to fault-in and retry if it worked */
                if (!user_event_mm_fault_in(user_mm, uaddr, attempt))
                        goto retry;
        }

        return result;
}

/*
 * Unregisters an enablement address/bit within a task/user mm.
 */
static long user_events_ioctl_unreg(unsigned long uarg)
{
        struct user_unreg __user *ureg = (struct user_unreg __user *)uarg;
        struct user_event_mm *mm = current->user_event_mm;
        struct user_event_enabler *enabler, *next;
        struct user_unreg reg;
        unsigned long flags;
        long ret;

        ret = user_unreg_get(ureg, &reg);

        if (ret)
                return ret;

        if (!mm)
                return -ENOENT;

        flags = 0;
        ret = -ENOENT;

        /*
         * Flags freeing and faulting are used to indicate if the enabler is in
         * use at all. When faulting is set a page-fault is occurring asyncly.
         * During async fault if freeing is set, the enabler will be destroyed.
         * If no async fault is happening, we can destroy it now since we hold
         * the event_mutex during these checks.
         */
        mutex_lock(&event_mutex);

        list_for_each_entry_safe(enabler, next, &mm->enablers, mm_enablers_link) {
                if (enabler->addr == reg.disable_addr &&
                    ENABLE_BIT(enabler) == reg.disable_bit) {
                        set_bit(ENABLE_VAL_FREEING_BIT, ENABLE_BITOPS(enabler));

                        /* We must keep compat flags for the clear */
                        flags |= enabler->values & ENABLE_VAL_COMPAT_MASK;

                        if (!test_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)))
                                user_event_enabler_destroy(enabler, true);

                        /* Removed at least one */
                        ret = 0;
                }
        }

        mutex_unlock(&event_mutex);

        /* Ensure bit is now cleared for user, regardless of event status */
        if (!ret)
                ret = user_event_mm_clear_bit(mm, reg.disable_addr,
                                              reg.disable_bit, flags);

        return ret;
}

/*
 * Handles the ioctl from user mode to register or alter operations.
 */
static long user_events_ioctl(struct file *file, unsigned int cmd,
                              unsigned long uarg)
{
        struct user_event_file_info *info = file->private_data;
        struct user_event_group *group = info->group;
        long ret = -ENOTTY;

        switch (cmd) {
        case DIAG_IOCSREG:
                mutex_lock(&group->reg_mutex);
                ret = user_events_ioctl_reg(info, uarg);
                mutex_unlock(&group->reg_mutex);
                break;

        case DIAG_IOCSDEL:
                mutex_lock(&group->reg_mutex);
                ret = user_events_ioctl_del(info, uarg);
                mutex_unlock(&group->reg_mutex);
                break;

        case DIAG_IOCSUNREG:
                mutex_lock(&group->reg_mutex);
                ret = user_events_ioctl_unreg(uarg);
                mutex_unlock(&group->reg_mutex);
                break;
        }

        return ret;
}

/*
 * Handles the final close of the file from user mode.
 */
static int user_events_release(struct inode *node, struct file *file)
{
        struct user_event_file_info *info = file->private_data;
        struct user_event_group *group;
        struct user_event_refs *refs;
        int i;

        if (!info)
                return -EINVAL;

        group = info->group;

        /*
         * Ensure refs cannot change under any situation by taking the
         * register mutex during the final freeing of the references.
         */
        mutex_lock(&group->reg_mutex);

        refs = info->refs;

        if (!refs)
                goto out;

        /*
         * The lifetime of refs has reached an end, it's tied to this file.
         * The underlying user_events are ref counted, and cannot be freed.
         * After this decrement, the user_events may be freed elsewhere.
         */
        for (i = 0; i < refs->count; ++i)
                user_event_put(refs->events[i], false);

out:
        file->private_data = NULL;

        mutex_unlock(&group->reg_mutex);

        kfree(refs);
        kfree(info);

        return 0;
}

static const struct file_operations user_data_fops = {
        .open           = user_events_open,
        .write          = user_events_write,
        .write_iter     = user_events_write_iter,
        .unlocked_ioctl = user_events_ioctl,
        .release        = user_events_release,
};

static void *user_seq_start(struct seq_file *m, loff_t *pos)
{
        if (*pos)
                return NULL;

        return (void *)1;
}

static void *user_seq_next(struct seq_file *m, void *p, loff_t *pos)
{
        ++*pos;
        return NULL;
}

static void user_seq_stop(struct seq_file *m, void *p)
{
}

static int user_seq_show(struct seq_file *m, void *p)
{
        struct user_event_group *group = m->private;
        struct user_event *user;
        char status;
        int i, active = 0, busy = 0;

        if (!group)
                return -EINVAL;

        mutex_lock(&group->reg_mutex);

        hash_for_each(group->register_table, i, user, node) {
                status = user->status;

                seq_printf(m, "%s", EVENT_TP_NAME(user));

                if (status != 0) {
                        seq_puts(m, " # Used by");
                        if (status & EVENT_STATUS_FTRACE)
                                seq_puts(m, " ftrace");
                        if (status & EVENT_STATUS_PERF)
                                seq_puts(m, " perf");
                        if (status & EVENT_STATUS_OTHER)
                                seq_puts(m, " other");
                        busy++;
                }

                seq_puts(m, "\n");
                active++;
        }

        mutex_unlock(&group->reg_mutex);

        seq_puts(m, "\n");
        seq_printf(m, "Active: %d\n", active);
        seq_printf(m, "Busy: %d\n", busy);

        return 0;
}

static const struct seq_operations user_seq_ops = {
        .start  = user_seq_start,
        .next   = user_seq_next,
        .stop   = user_seq_stop,
        .show   = user_seq_show,
};

static int user_status_open(struct inode *node, struct file *file)
{
        struct user_event_group *group;
        int ret;

        group = current_user_event_group();

        if (!group)
                return -ENOENT;

        ret = seq_open(file, &user_seq_ops);

        if (!ret) {
                /* Chain group to seq_file */
                struct seq_file *m = file->private_data;

                m->private = group;
        }

        return ret;
}

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

/*
 * Creates a set of tracefs files to allow user mode interactions.
 */
static int create_user_tracefs(void)
{
        struct dentry *edata, *emmap;

        edata = tracefs_create_file("user_events_data", TRACE_MODE_WRITE,
                                    NULL, NULL, &user_data_fops);

        if (!edata) {
                pr_warn("Could not create tracefs 'user_events_data' entry\n");
                goto err;
        }

        emmap = tracefs_create_file("user_events_status", TRACE_MODE_READ,
                                    NULL, NULL, &user_status_fops);

        if (!emmap) {
                tracefs_remove(edata);
                pr_warn("Could not create tracefs 'user_events_mmap' entry\n");
                goto err;
        }

        return 0;
err:
        return -ENODEV;
}

static int set_max_user_events_sysctl(const struct ctl_table *table, int write,
                                      void *buffer, size_t *lenp, loff_t *ppos)
{
        int ret;

        mutex_lock(&event_mutex);

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

        mutex_unlock(&event_mutex);

        return ret;
}

static const struct ctl_table user_event_sysctls[] = {
        {
                .procname       = "user_events_max",
                .data           = &max_user_events,
                .maxlen         = sizeof(unsigned int),
                .mode           = 0644,
                .proc_handler   = set_max_user_events_sysctl,
        },
};

static int __init trace_events_user_init(void)
{
        int ret;

        fault_cache = KMEM_CACHE(user_event_enabler_fault, 0);

        if (!fault_cache)
                return -ENOMEM;

        init_group = user_event_group_create();

        if (!init_group) {
                kmem_cache_destroy(fault_cache);
                return -ENOMEM;
        }

        ret = create_user_tracefs();

        if (ret) {
                pr_warn("user_events could not register with tracefs\n");
                user_event_group_destroy(init_group);
                kmem_cache_destroy(fault_cache);
                init_group = NULL;
                return ret;
        }

        if (dyn_event_register(&user_event_dops))
                pr_warn("user_events could not register with dyn_events\n");

        register_sysctl_init("kernel", user_event_sysctls);

        return 0;
}

fs_initcall(trace_events_user_init);