Re: [PATCH] drm/syncobj: Stop reusing the same struct file for all syncobj -> fd

[Jani Nikula <jani.nikula@linux.intel.com>]

commit e7cdf5c82f1773c3386b93bbcf13b9bfff29fa31 upstream.

BR,
Jani.

On Mon, 26 Mar 2018, Jason Ekstrand <jason@jlekstrand.net> wrote:
> From: Chris Wilson <chris@chris-wilson.co.uk>
>
> The vk cts test:
> dEQP-VK.api.external.semaphore.opaque_fd.export_multiple_times_temporary
>
> triggers a lot of
> VFS: Close: file count is 0
>
> Dave pointed out that clearing the syncobj->file from
> drm_syncobj_file_release() was sufficient to silence the test, but that
> opens a can of worm since we assumed that the syncobj->file was never
> unset. Stop trying to reuse the same struct file for every fd pointing
> to the drm_syncobj, and allocate one file for each fd instead.
>
> v2: Fixup return handling of drm_syncobj_fd_to_handle
> v2.1: [airlied: fix possible syncobj ref race]
> v2.2: [jekstrand: back-port to 4.14]
>
> Reported-by: Dave Airlie <airlied@redhat.com>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Tested-by: Dave Airlie <airlied@redhat.com>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Dave Airlie <airlied@redhat.com>
> Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
> Tested-by: Clayton Craft <clayton.a.craft@intel.com>
> ---
>
> The back-port from 4.15 to 4.14 was non-trivial.  It'd be good if Chris and
> maybe Daniel could do a quick re-review.
>
>  drivers/gpu/drm/drm_syncobj.c | 81 ++++++++++++++++---------------------------
>  include/drm/drm_syncobj.h     |  5 ---
>  2 files changed, 30 insertions(+), 56 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index 0422b8c..7bcf570 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -328,28 +328,11 @@ static const struct file_operations drm_syncobj_file_fops = {
>  	.release = drm_syncobj_file_release,
>  };
>  
> -static int drm_syncobj_alloc_file(struct drm_syncobj *syncobj)
> -{
> -	struct file *file = anon_inode_getfile("syncobj_file",
> -					       &drm_syncobj_file_fops,
> -					       syncobj, 0);
> -	if (IS_ERR(file))
> -		return PTR_ERR(file);
> -
> -	drm_syncobj_get(syncobj);
> -	if (cmpxchg(&syncobj->file, NULL, file)) {
> -		/* lost the race */
> -		fput(file);
> -	}
> -
> -	return 0;
> -}
> -
>  static int drm_syncobj_handle_to_fd(struct drm_file *file_private,
>  				    u32 handle, int *p_fd)
>  {
>  	struct drm_syncobj *syncobj = drm_syncobj_find(file_private, handle);
> -	int ret;
> +	struct file *file;
>  	int fd;
>  
>  	if (!syncobj)
> @@ -361,46 +344,40 @@ static int drm_syncobj_handle_to_fd(struct drm_file *file_private,
>  		return fd;
>  	}
>  
> -	if (!syncobj->file) {
> -		ret = drm_syncobj_alloc_file(syncobj);
> -		if (ret)
> -			goto out_put_fd;
> +	file = anon_inode_getfile("syncobj_file",
> +				  &drm_syncobj_file_fops,
> +				  syncobj, 0);
> +	if (IS_ERR(file)) {
> +		put_unused_fd(fd);
> +		drm_syncobj_put(syncobj);
> +		return PTR_ERR(file);
>  	}
> -	fd_install(fd, syncobj->file);
> -	drm_syncobj_put(syncobj);
> +
> +	drm_syncobj_get(syncobj);
> +	fd_install(fd, file);
> +
>  	*p_fd = fd;
>  	return 0;
> -out_put_fd:
> -	put_unused_fd(fd);
> -	drm_syncobj_put(syncobj);
> -	return ret;
>  }
>  
> -static struct drm_syncobj *drm_syncobj_fdget(int fd)
> -{
> -	struct file *file = fget(fd);
> -
> -	if (!file)
> -		return NULL;
> -	if (file->f_op != &drm_syncobj_file_fops)
> -		goto err;
> -
> -	return file->private_data;
> -err:
> -	fput(file);
> -	return NULL;
> -};
> -
>  static int drm_syncobj_fd_to_handle(struct drm_file *file_private,
>  				    int fd, u32 *handle)
>  {
> -	struct drm_syncobj *syncobj = drm_syncobj_fdget(fd);
> +	struct drm_syncobj *syncobj;
> +	struct file *file;
>  	int ret;
>  
> -	if (!syncobj)
> +	file = fget(fd);
> +	if (!file)
> +		return -EINVAL;
> +
> +	if (file->f_op != &drm_syncobj_file_fops) {
> +		fput(file);
>  		return -EINVAL;
> +	}
>  
>  	/* take a reference to put in the idr */
> +	syncobj = file->private_data;
>  	drm_syncobj_get(syncobj);
>  
>  	idr_preload(GFP_KERNEL);
> @@ -409,12 +386,14 @@ static int drm_syncobj_fd_to_handle(struct drm_file *file_private,
>  	spin_unlock(&file_private->syncobj_table_lock);
>  	idr_preload_end();
>  
> -	if (ret < 0) {
> -		fput(syncobj->file);
> -		return ret;
> -	}
> -	*handle = ret;
> -	return 0;
> +	if (ret > 0) {
> +		*handle = ret;
> +		ret = 0;
> +	} else
> +		drm_syncobj_put(syncobj);
> +
> +	fput(file);
> +	return ret;
>  }
>  
>  int drm_syncobj_import_sync_file_fence(struct drm_file *file_private,
> diff --git a/include/drm/drm_syncobj.h b/include/drm/drm_syncobj.h
> index c00fee5..6d45aae 100644
> --- a/include/drm/drm_syncobj.h
> +++ b/include/drm/drm_syncobj.h
> @@ -60,11 +60,6 @@ struct drm_syncobj {
>  	 * locks cb_list and write-locks fence.
>  	 */
>  	spinlock_t lock;
> -	/**
> -	 * @file:
> -	 * a file backing for this syncobj.
> -	 */
> -	struct file *file;
>  };
>  
>  typedef void (*drm_syncobj_func_t)(struct drm_syncobj *syncobj,

-- 
Jani Nikula, Intel Open Source Technology Center