Re: [PATCH v2] drm/virtio: fix resource id creation race

2020-02-24 Thread Gerd Hoffmann 
On Thu, Feb 20, 2020 at 02:53:19PM -0800, John Bates wrote:
> 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: John Bates 

Pushed to drm-misc-fixes.

thanks,
  Gerd

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Re: [PATCH v2] drm/virtio: fix resource id creation race

2020-02-21 Thread Chia-I Wu 
On Fri, Feb 21, 2020 at 3:14 AM John Bates  wrote:
>
> 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: John Bates 
Reviewed-by: Chia-I Wu 
> ---
>  drivers/gpu/drm/virtio/virtgpu_object.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c 
> b/drivers/gpu/drm/virtio/virtgpu_object.c
> index 017a9e0fc3bb..890121a45625 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_object.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_object.c
> @@ -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();
> *resid = handle + 1;
resid 1 is (was) discriminated :D

> } else {
> int handle = ida_alloc(>resource_ida, GFP_KERNEL);
> --
> 2.25.0.265.gbab2e86ba0-goog
>
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[PATCH v2] drm/virtio: fix resource id creation race

2020-02-21 Thread John Bates 
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: John Bates 
---
 drivers/gpu/drm/virtio/virtgpu_object.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c 
b/drivers/gpu/drm/virtio/virtgpu_object.c
index 017a9e0fc3bb..890121a45625 100644
--- a/drivers/gpu/drm/virtio/virtgpu_object.c
+++ b/drivers/gpu/drm/virtio/virtgpu_object.c
@@ -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();
*resid = handle + 1;
} else {
int handle = ida_alloc(>resource_ida, GFP_KERNEL);
-- 
2.25.0.265.gbab2e86ba0-goog

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