答复: [PATCH] drm/amdgpu:fix race condition

[Liu, Monk]

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

But what if user land pass in seq 0 on purpose , but the latest cring->sequence value is only 3 ?
Without this "if (seq == 0)" the logic seems goes to a wrong direction

BR Monk

-----邮件原件-----
发件人: Christian König [mailto:deathsimple at vodafone.de] 
发送时间: Monday, April 10, 2017 3:22 PM
收件人: Liu, Monk <Monk.Liu at amd.com>; amd-gfx at lists.freedesktop.org
主题: Re: [PATCH] drm/amdgpu:fix race condition

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);