Re: [PATCH] drm/exynos: use a new anon file for exynos gem mmaper

[Daniel Vetter <daniel@ffwll.ch>]

Ok I've stumbled over the exynos mmap stuff again while cleaning up
drm legacy cruft and I just don't get what you're doing and why
exactly exynos needs to be special.

_All_ other drm drivers happily get along with the vma offset manger
stuff to handle mmaps, but somehow exynos does something really crazy.

Can you please explain the design justification for this and why
switching to the standard gem mmap support isn't possible?

Thanks, Daniel


On Fri, Dec 20, 2013 at 11:36 AM, Inki Dae <inki.dae@samsung.com> wrote:
> This patch resolves potential deadlock issue that can be incurred
> by changing file->f_op and filp->private_data to exynos specific
> mapper ops and gem object temporarily.
>
> To resolve this issue, this patch creates a new anon file dedicated
> to exynos specific mmaper, and making it used instead of existing one.
>
> Signed-off-by: Inki Dae <inki.dae@samsung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
> ---
>  drivers/gpu/drm/exynos/exynos_drm_drv.c |   21 +++++++++
>  drivers/gpu/drm/exynos/exynos_drm_drv.h |    1 +
>  drivers/gpu/drm/exynos/exynos_drm_gem.c |   74 ++++++-------------------------
>  drivers/gpu/drm/exynos/exynos_drm_gem.h |    3 ++
>  4 files changed, 38 insertions(+), 61 deletions(-)
>
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_drv.c b/drivers/gpu/drm/exynos/exynos_drm_drv.c
> index 22b8f5e..b5e5957 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_drv.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_drv.c
> @@ -14,6 +14,8 @@
>  #include <drm/drmP.h>
>  #include <drm/drm_crtc_helper.h>
>
> +#include <linux/anon_inodes.h>
> +
>  #include <drm/exynos_drm.h>
>
>  #include "exynos_drm_drv.h"
> @@ -150,9 +152,14 @@ static int exynos_drm_unload(struct drm_device *dev)
>         return 0;
>  }
>
> +static const struct file_operations exynos_drm_gem_fops = {
> +       .mmap = exynos_drm_gem_mmap_buffer,
> +};
> +
>  static int exynos_drm_open(struct drm_device *dev, struct drm_file *file)
>  {
>         struct drm_exynos_file_private *file_priv;
> +       struct file *anon_filp;
>         int ret;
>
>         file_priv = kzalloc(sizeof(*file_priv), GFP_KERNEL);
> @@ -167,6 +174,16 @@ static int exynos_drm_open(struct drm_device *dev, struct drm_file *file)
>                 file->driver_priv = NULL;
>         }
>
> +       anon_filp = anon_inode_getfile("exynos_gem", &exynos_drm_gem_fops,
> +                                       NULL, 0);
> +       if (IS_ERR(anon_filp)) {
> +               kfree(file_priv);
> +               return PTR_ERR(anon_filp);
> +       }
> +
> +       anon_filp->f_mode = FMODE_READ | FMODE_WRITE;
> +       file_priv->anon_filp = anon_filp;
> +
>         return ret;
>  }
>
> @@ -179,6 +196,7 @@ static void exynos_drm_preclose(struct drm_device *dev,
>  static void exynos_drm_postclose(struct drm_device *dev, struct drm_file *file)
>  {
>         struct exynos_drm_private *private = dev->dev_private;
> +       struct drm_exynos_file_private *file_priv;
>         struct drm_pending_vblank_event *v, *vt;
>         struct drm_pending_event *e, *et;
>         unsigned long flags;
> @@ -204,6 +222,9 @@ static void exynos_drm_postclose(struct drm_device *dev, struct drm_file *file)
>         }
>         spin_unlock_irqrestore(&dev->event_lock, flags);
>
> +       file_priv = file->driver_priv;
> +       if (file_priv->anon_filp)
> +               fput(file_priv->anon_filp);
>
>         kfree(file->driver_priv);
>         file->driver_priv = NULL;
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_drv.h b/drivers/gpu/drm/exynos/exynos_drm_drv.h
> index eaa1966..0eaf5a2 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_drv.h
> +++ b/drivers/gpu/drm/exynos/exynos_drm_drv.h
> @@ -226,6 +226,7 @@ struct exynos_drm_ipp_private {
>  struct drm_exynos_file_private {
>         struct exynos_drm_g2d_private   *g2d_priv;
>         struct exynos_drm_ipp_private   *ipp_priv;
> +       struct file                     *anon_filp;
>  };
>
>  /*
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_gem.c b/drivers/gpu/drm/exynos/exynos_drm_gem.c
> index 1ade191..49b8c9b 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_gem.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_gem.c
> @@ -338,46 +338,22 @@ int exynos_drm_gem_map_offset_ioctl(struct drm_device *dev, void *data,
>                         &args->offset);
>  }
>
> -static struct drm_file *exynos_drm_find_drm_file(struct drm_device *drm_dev,
> -                                                       struct file *filp)
> -{
> -       struct drm_file *file_priv;
> -
> -       /* find current process's drm_file from filelist. */
> -       list_for_each_entry(file_priv, &drm_dev->filelist, lhead)
> -               if (file_priv->filp == filp)
> -                       return file_priv;
> -
> -       WARN_ON(1);
> -
> -       return ERR_PTR(-EFAULT);
> -}
> -
> -static int exynos_drm_gem_mmap_buffer(struct file *filp,
> +int exynos_drm_gem_mmap_buffer(struct file *filp,
>                                       struct vm_area_struct *vma)
>  {
>         struct drm_gem_object *obj = filp->private_data;
>         struct exynos_drm_gem_obj *exynos_gem_obj = to_exynos_gem_obj(obj);
>         struct drm_device *drm_dev = obj->dev;
>         struct exynos_drm_gem_buf *buffer;
> -       struct drm_file *file_priv;
>         unsigned long vm_size;
>         int ret;
>
> +       WARN_ON(!mutex_is_locked(&obj->dev->struct_mutex));
> +
>         vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
>         vma->vm_private_data = obj;
>         vma->vm_ops = drm_dev->driver->gem_vm_ops;
>
> -       /* restore it to driver's fops. */
> -       filp->f_op = fops_get(drm_dev->driver->fops);
> -
> -       file_priv = exynos_drm_find_drm_file(drm_dev, filp);
> -       if (IS_ERR(file_priv))
> -               return PTR_ERR(file_priv);
> -
> -       /* restore it to drm_file. */
> -       filp->private_data = file_priv;
> -
>         update_vm_cache_attr(exynos_gem_obj, vma);
>
>         vm_size = vma->vm_end - vma->vm_start;
> @@ -411,15 +387,13 @@ static int exynos_drm_gem_mmap_buffer(struct file *filp,
>         return 0;
>  }
>
> -static const struct file_operations exynos_drm_gem_fops = {
> -       .mmap = exynos_drm_gem_mmap_buffer,
> -};
> -
>  int exynos_drm_gem_mmap_ioctl(struct drm_device *dev, void *data,
>                               struct drm_file *file_priv)
>  {
> +       struct drm_exynos_file_private *exynos_file_priv;
>         struct drm_exynos_gem_mmap *args = data;
>         struct drm_gem_object *obj;
> +       struct file *anon_filp;
>         unsigned long addr;
>
>         if (!(dev->driver->driver_features & DRIVER_GEM)) {
> @@ -427,47 +401,25 @@ int exynos_drm_gem_mmap_ioctl(struct drm_device *dev, void *data,
>                 return -ENODEV;
>         }
>
> +       mutex_lock(&dev->struct_mutex);
> +
>         obj = drm_gem_object_lookup(dev, file_priv, args->handle);
>         if (!obj) {
>                 DRM_ERROR("failed to lookup gem object.\n");
> +               mutex_unlock(&dev->struct_mutex);
>                 return -EINVAL;
>         }
>
> -       /*
> -        * We have to use gem object and its fops for specific mmaper,
> -        * but vm_mmap() can deliver only filp. So we have to change
> -        * filp->f_op and filp->private_data temporarily, then restore
> -        * again. So it is important to keep lock until restoration the
> -        * settings to prevent others from misuse of filp->f_op or
> -        * filp->private_data.
> -        */
> -       mutex_lock(&dev->struct_mutex);
> -
> -       /*
> -        * Set specific mmper's fops. And it will be restored by
> -        * exynos_drm_gem_mmap_buffer to dev->driver->fops.
> -        * This is used to call specific mapper temporarily.
> -        */
> -       file_priv->filp->f_op = &exynos_drm_gem_fops;
> -
> -       /*
> -        * Set gem object to private_data so that specific mmaper
> -        * can get the gem object. And it will be restored by
> -        * exynos_drm_gem_mmap_buffer to drm_file.
> -        */
> -       file_priv->filp->private_data = obj;
> +       exynos_file_priv = file_priv->driver_priv;
> +       anon_filp = exynos_file_priv->anon_filp;
> +       anon_filp->private_data = obj;
>
> -       addr = vm_mmap(file_priv->filp, 0, args->size,
> -                       PROT_READ | PROT_WRITE, MAP_SHARED, 0);
> +       addr = vm_mmap(anon_filp, 0, args->size, PROT_READ | PROT_WRITE,
> +                       MAP_SHARED, 0);
>
>         drm_gem_object_unreference(obj);
>
>         if (IS_ERR_VALUE(addr)) {
> -               /* check filp->f_op, filp->private_data are restored */
> -               if (file_priv->filp->f_op == &exynos_drm_gem_fops) {
> -                       file_priv->filp->f_op = fops_get(dev->driver->fops);
> -                       file_priv->filp->private_data = file_priv;
> -               }
>                 mutex_unlock(&dev->struct_mutex);
>                 return (int)addr;
>         }
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_gem.h b/drivers/gpu/drm/exynos/exynos_drm_gem.h
> index 702ec3a..fde860c 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_gem.h
> +++ b/drivers/gpu/drm/exynos/exynos_drm_gem.h
> @@ -122,6 +122,9 @@ int exynos_drm_gem_map_offset_ioctl(struct drm_device *dev, void *data,
>  int exynos_drm_gem_mmap_ioctl(struct drm_device *dev, void *data,
>                               struct drm_file *file_priv);
>
> +int exynos_drm_gem_mmap_buffer(struct file *filp,
> +                                     struct vm_area_struct *vma);
> +
>  /* map user space allocated by malloc to pages. */
>  int exynos_drm_gem_userptr_ioctl(struct drm_device *dev, void *data,
>                                       struct drm_file *file_priv);
> --
> 1.7.9.5
>
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch