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UPSTREAM: drm/virtio: fix resource id creation race

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commit fbb30168c7 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: 16065fcdd1 ("drm/virtio: do NOT reuse resource ids")
Signed-off-by: John Bates <jbates@chromium.org>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200220225319.45621-1-jbates@chromium.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 9998ebb5e7)
Bug: 153580313
Signed-off-by: Alistair Delva <adelva@google.com>
Change-Id: Iad0ca447e5be8b8098962b50e8d38356d1024126
This commit is contained in:
John Bates
2020-02-20 14:53:19 -08:00
committed by Alistair Delva
parent 380c5c0d07
commit 2236a7f126
1 changed files with 2 additions and 2 deletions
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4
drivers/gpu/drm/virtio/virtgpu_object.c
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@@ -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);