drivers/dma-buf/sw_sync.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Sync File validation framework
 *
 * Copyright (C) 2012 Google, Inc.
 */

#include <linux/file.h>
#include <linux/fs.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/uaccess.h>
#include <linux/slab.h>
#include <linux/sync_file.h>

#include "sync_debug.h"

#define CREATE_TRACE_POINTS
#include "sync_trace.h"

/*
 * SW SYNC validation framework
 *
 * A sync object driver that uses a 32bit counter to coordinate
 * synchronization.  Useful when there is no hardware primitive backing
 * the synchronization.
 *
 * To start the framework just open:
 *
 * <debugfs>/sync/sw_sync
 *
 * That will create a sync timeline, all fences created under this timeline
 * file descriptor will belong to the this timeline.
 *
 * The 'sw_sync' file can be opened many times as to create different
 * timelines.
 *
 * Fences can be created with SW_SYNC_IOC_CREATE_FENCE ioctl with struct
 * sw_sync_create_fence_data as parameter.
 *
 * To increment the timeline counter, SW_SYNC_IOC_INC ioctl should be used
 * with the increment as u32. This will update the last signaled value
 * from the timeline and signal any fence that has a seqno smaller or equal
 * to it.
 *
 * struct sw_sync_create_fence_data
 * @value:    the seqno to initialise the fence with
 * @name:    the name of the new sync point
 * @fence:    return the fd of the new sync_file with the created fence
 */
struct sw_sync_create_fence_data {
    __u32 value;
    char name[32];
    __s32 fence; /* fd of new fence */
};

#define SW_SYNC_IOC_MAGIC 'W'

#define SW_SYNC_IOC_CREATE_FENCE _IOWR(SW_SYNC_IOC_MAGIC, 0, struct sw_sync_create_fence_data)

#define SW_SYNC_IOC_INC _IOW(SW_SYNC_IOC_MAGIC, 1, __u32)

static const struct dma_fence_ops timeline_fence_ops;

static inline struct sync_pt *dma_fence_to_sync_pt(struct dma_fence *fence)
{
    if (fence->ops != &timeline_fence_ops) {
        return NULL;
    }
    return container_of(fence, struct sync_pt, base);
}

/**
 * sync_timeline_create() - creates a sync object
 * @name:    sync_timeline name
 *
 * Creates a new sync_timeline. Returns the sync_timeline object or NULL in
 * case of error.
 */
static struct sync_timeline *sync_timeline_create(const char *name)
{
    struct sync_timeline *obj;

    obj = kzalloc(sizeof(*obj), GFP_KERNEL);
    if (!obj) {
        return NULL;
    }

    kref_init(&obj->kref);
    obj->context = dma_fence_context_alloc(1);
    strlcpy(obj->name, name, sizeof(obj->name));

    obj->pt_tree = RB_ROOT;
    INIT_LIST_HEAD(&obj->pt_list);
    spin_lock_init(&obj->lock);

    sync_timeline_debug_add(obj);

    return obj;
}

static void sync_timeline_free(struct kref *kref)
{
    struct sync_timeline *obj = container_of(kref, struct sync_timeline, kref);

    sync_timeline_debug_remove(obj);

    kfree(obj);
}

static void sync_timeline_get(struct sync_timeline *obj)
{
    kref_get(&obj->kref);
}

static void sync_timeline_put(struct sync_timeline *obj)
{
    kref_put(&obj->kref, sync_timeline_free);
}

static const char *timeline_fence_get_driver_name(struct dma_fence *fence)
{
    return "sw_sync";
}

static const char *timeline_fence_get_timeline_name(struct dma_fence *fence)
{
    struct sync_timeline *parent = dma_fence_parent(fence);

    return parent->name;
}

static void timeline_fence_release(struct dma_fence *fence)
{
    struct sync_pt *pt = dma_fence_to_sync_pt(fence);
    struct sync_timeline *parent = dma_fence_parent(fence);
    unsigned long flags;

    spin_lock_irqsave(fence->lock, flags);
    if (!list_empty(&pt->link)) {
        list_del(&pt->link);
        rb_erase(&pt->node, &parent->pt_tree);
    }
    spin_unlock_irqrestore(fence->lock, flags);

    sync_timeline_put(parent);
    dma_fence_free(fence);
}

static bool timeline_fence_signaled(struct dma_fence *fence)
{
    struct sync_timeline *parent = dma_fence_parent(fence);

    return !__dma_fence_is_later(fence->seqno, parent->value, fence->ops);
}

static bool timeline_fence_enable_signaling(struct dma_fence *fence)
{
    return true;
}

static void timeline_fence_value_str(struct dma_fence *fence, char *str, int size)
{
    int ret = 0;
    ret = snprintf(str, size, "%lld", fence->seqno);
}

static void timeline_fence_timeline_value_str(struct dma_fence *fence, char *str, int size)
{
    struct sync_timeline *parent = dma_fence_parent(fence);
    int ret = 0;
    ret = snprintf(str, size, "%d", parent->value);
}

static const struct dma_fence_ops timeline_fence_ops = {
    .get_driver_name = timeline_fence_get_driver_name,
    .get_timeline_name = timeline_fence_get_timeline_name,
    .enable_signaling = timeline_fence_enable_signaling,
    .signaled = timeline_fence_signaled,
    .release = timeline_fence_release,
    .fence_value_str = timeline_fence_value_str,
    .timeline_value_str = timeline_fence_timeline_value_str,
};

/**
 * sync_timeline_signal() - signal a status change on a sync_timeline
 * @obj:    sync_timeline to signal
 * @inc:    num to increment on timeline->value
 *
 * A sync implementation should call this any time one of it's fences
 * has signaled or has an error condition.
 */
static void sync_timeline_signal(struct sync_timeline *obj, unsigned int inc)
{
    struct sync_pt *pt, *next;

    trace_sync_timeline(obj);

    spin_lock_irq(&obj->lock);

    obj->value += inc;

    list_for_each_entry_safe(pt, next, &obj->pt_list, link)
    {
        if (!timeline_fence_signaled(&pt->base)) {
            break;
        }

        list_del_init(&pt->link);
        rb_erase(&pt->node, &obj->pt_tree);

        /*
         * A signal callback may release the last reference to this
         * fence, causing it to be freed. That operation has to be
         * last to avoid a use after free inside this loop, and must
         * be after we remove the fence from the timeline in order to
         * prevent deadlocking on timeline->lock inside
         * timeline_fence_release().
         */
        dma_fence_signal_locked(&pt->base);
    }

    spin_unlock_irq(&obj->lock);
}

/**
 * sync_pt_create() - creates a sync pt
 * @obj:    parent sync_timeline
 * @value:    value of the fence
 *
 * Creates a new sync_pt (fence) as a child of @parent.  @size bytes will be
 * allocated allowing for implementation specific data to be kept after
 * the generic sync_timeline struct. Returns the sync_pt object or
 * NULL in case of error.
 */
static struct sync_pt *sync_pt_create(struct sync_timeline *obj, unsigned int value)
{
    struct sync_pt *pt;

    pt = kzalloc(sizeof(*pt), GFP_KERNEL);
    if (!pt) {
        return NULL;
    }

    sync_timeline_get(obj);
    dma_fence_init(&pt->base, &timeline_fence_ops, &obj->lock, obj->context, value);
    INIT_LIST_HEAD(&pt->link);

    spin_lock_irq(&obj->lock);
    if (!dma_fence_is_signaled_locked(&pt->base)) {
        struct rb_node **p = &obj->pt_tree.rb_node;
        struct rb_node *parent = NULL;

        while (*p) {
            struct sync_pt *other;
            int cmp;

            parent = *p;
            other = rb_entry(parent, typeof(*pt), node);
            cmp = value - other->base.seqno;
            if (cmp > 0) {
                p = &parent->rb_right;
            } else if (cmp < 0) {
                p = &parent->rb_left;
            } else {
                if (dma_fence_get_rcu(&other->base)) {
                    sync_timeline_put(obj);
                    kfree(pt);
                    pt = other;
                    goto unlock;
                }
                p = &parent->rb_left;
            }
        }
        rb_link_node(&pt->node, parent, p);
        rb_insert_color(&pt->node, &obj->pt_tree);

        parent = rb_next(&pt->node);
        list_add_tail(&pt->link, parent ? &rb_entry(parent, typeof(*pt), node)->link : &obj->pt_list);
    }
unlock:
    spin_unlock_irq(&obj->lock);

    return pt;
}

/*
 * *WARNING*
 *
 * improper use of this can result in deadlocking kernel drivers from userspace.
 */

/* opening sw_sync create a new sync obj */
static int sw_sync_debugfs_open(struct inode *inode, struct file *file)
{
    struct sync_timeline *obj;
    char task_comm[TASK_COMM_LEN];

    get_task_comm(task_comm, current);

    obj = sync_timeline_create(task_comm);
    if (!obj) {
        return -ENOMEM;
    }

    file->private_data = obj;

    return 0;
}

static int sw_sync_debugfs_release(struct inode *inode, struct file *file)
{
    struct sync_timeline *obj = file->private_data;
    struct sync_pt *pt, *next;

    spin_lock_irq(&obj->lock);

    list_for_each_entry_safe(pt, next, &obj->pt_list, link)
    {
        dma_fence_set_error(&pt->base, -ENOENT);
        dma_fence_signal_locked(&pt->base);
    }

    spin_unlock_irq(&obj->lock);

    sync_timeline_put(obj);
    return 0;
}

static long sw_sync_ioctl_create_fence(struct sync_timeline *obj, unsigned long arg)
{
    int fd = get_unused_fd_flags(O_CLOEXEC);
    int err;
    struct sync_pt *pt;
    struct sync_file *sync_file;
    struct sw_sync_create_fence_data data;

    if (fd < 0) {
        return fd;
    }

    if (copy_from_user(&data, (void __user *)arg, sizeof(data))) {
        err = -EFAULT;
        goto err;
    }

    pt = sync_pt_create(obj, data.value);
    if (!pt) {
        err = -ENOMEM;
        goto err;
    }

    sync_file = sync_file_create(&pt->base);
    dma_fence_put(&pt->base);
    if (!sync_file) {
        err = -ENOMEM;
        goto err;
    }

    data.fence = fd;
    if (copy_to_user((void __user *)arg, &data, sizeof(data))) {
        fput(sync_file->file);
        err = -EFAULT;
        goto err;
    }

    fd_install(fd, sync_file->file);

    return 0;

err:
    put_unused_fd(fd);
    return err;
}

static long sw_sync_ioctl_inc(struct sync_timeline *obj, unsigned long arg)
{
    u32 value;

    if (copy_from_user(&value, (void __user *)arg, sizeof(value))) {
        return -EFAULT;
    }

    while (value > INT_MAX) {
        sync_timeline_signal(obj, INT_MAX);
        value -= INT_MAX;
    }

    sync_timeline_signal(obj, value);

    return 0;
}

static long sw_sync_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
    struct sync_timeline *obj = file->private_data;

    switch (cmd) {
        case SW_SYNC_IOC_CREATE_FENCE:
            return sw_sync_ioctl_create_fence(obj, arg);

        case SW_SYNC_IOC_INC:
            return sw_sync_ioctl_inc(obj, arg);

        default:
            return -ENOTTY;
    }
}

const struct file_operations sw_sync_debugfs_fops = {
    .open = sw_sync_debugfs_open,
    .release = sw_sync_debugfs_release,
    .unlocked_ioctl = sw_sync_ioctl,
    .compat_ioctl = compat_ptr_ioctl,
};

static struct miscdevice sw_sync_dev = {
    .minor = MISC_DYNAMIC_MINOR,
    .name = "sw_sync",
    .fops = &sw_sync_debugfs_fops,
};

module_misc_device(sw_sync_dev);

MODULE_LICENSE("GPL v2");