[PATCH] drm/amdgpu:fix race condition

[Christian König]

Am 10.04.2017 um 09:18 schrieb Monk Liu:
> sequence is protected by spinlock so don't access sequence
> in paramter seq when invoking this function.
>
> ~0 means to get the latest sequence number and 0 means none to
> get.
>
> Change-Id: Ib7a03f3cf5594deeb4ad333cc59b47a6bddfd1ad
> Signed-off-by: Monk Liu <Monk.Liu at amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
> index 6d86eae..71d5f25 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
> @@ -277,6 +277,13 @@ struct fence *amdgpu_ctx_get_fence(struct amdgpu_ctx *ctx,
>   
>   	spin_lock(&ctx->ring_lock);
>   
> +	if (seq == ~0) {

That must be ~0ull, otherwise you would be checking a 32bit value here.

Additional to that please define something in amdgpu_drm.h for that value.

> +		seq = ctx->rings[ring->idx].sequence - 1;
> +	} else if(seq == 0) {
> +		spin_unlock(&ctx->ring_lock);
> +		return NULL;
> +	}
> +

That is unnecessary the "if (seq + amdgpu_sched_jobs < cring->sequence) 
{" will catch this case.

Regards,
Christian.

>   	if (seq >= cring->sequence) {
>   		spin_unlock(&ctx->ring_lock);
>   		return ERR_PTR(-EINVAL);