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Commit 2236a7f1 authored by John Bates's avatar John Bates Committed by Alistair Delva
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UPSTREAM: drm/virtio: fix resource id creation race 



commit fbb30168c7395b9cfeb9e6f7b0c0bca854a6552d upstream.

The previous code was not thread safe and caused
undefined behavior from spurious duplicate resource IDs.
In this patch, an atomic_t is used instead. We no longer
see any duplicate IDs in tests with this change.

Fixes: 16065fcdd19d ("drm/virtio: do NOT reuse resource ids")
Signed-off-by: default avatarJohn Bates <jbates@chromium.org>
Reviewed-by: default avatarChia-I Wu <olvaffe@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200220225319.45621-1-jbates@chromium.org


Signed-off-by: default avatarGerd Hoffmann <kraxel@redhat.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 9998ebb5e73c72ba11a025434be9c2ff1c33b1f0)
Bug: 153580313
Signed-off-by: default avatarAlistair Delva <adelva@google.com>
Change-Id: Iad0ca447e5be8b8098962b50e8d38356d1024126
parent 380c5c0d

drivers/gpu/drm/virtio/virtgpu_object.c

+2 −2
Original line number Diff line number Diff line
@@ -42,8 +42,8 @@ static int virtio_gpu_resource_id_get(struct virtio_gpu_device *vgdev, 
		 * "f91a9dd35715 Fix unlinking resources from hash

		 * table." (Feb 2019) fixes the bug.

		 */

		static int handle;

		handle++;

		static atomic_t seqno = ATOMIC_INIT(0);

		int handle = atomic_inc_return(&seqno);

		*resid = handle + 1;

	} else {

		int handle = ida_alloc(&vgdev->resource_ida, GFP_KERNEL);