[Intel-gfx] [PATCH] drm/syncobj: Avoid kmalloc(GFP_KERNEL) under spinlock

[Christian König]

Am 26.10.18 um 08:20 schrieb Chunming Zhou:
> drivers/gpu/drm/drm_syncobj.c:202:4-14: ERROR: function drm_syncobj_find_signal_pt_for_point called on line 390 inside lock on line 389 but uses GFP_KERNEL
>
>    Find functions that refer to GFP_KERNEL but are called with locks held.
>
> Generated by: scripts/coccinelle/locks/call_kern.cocci
>
> v2:
> syncobj->timeline still needs protect.
>
> v3:
> use a global signaled fence instead of re-allocation.
>
> v4:
> Don't need moving lock.
> Don't expose func.
>
> v5:
> rename func and directly return.
>
> Tested by: syncobj_wait and ./deqp-vk -n dEQP-VK.*semaphore* with
> lock debug kernel options enabled.
>
> Signed-off-by: Chunming Zhou <david1.zhou at amd.com>
> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Cc: intel-gfx at lists.freedesktop.org
> Cc: Christian König <easy2remember.chk at googlemail.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> CC: Julia Lawall <julia.lawall at lip6.fr>
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

Reviewed-by: Christian König <christian.koenig at amd.com>

> ---
>   drivers/gpu/drm/drm_syncobj.c | 36 ++++++++++++++++++-----------------
>   1 file changed, 19 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index b7eaa603f368..d1c6f21c72b5 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -80,6 +80,23 @@ struct drm_syncobj_signal_pt {
>   	struct list_head list;
>   };
>   
> +static DEFINE_SPINLOCK(signaled_fence_lock);
> +static struct dma_fence signaled_fence;
> +
> +static struct dma_fence *drm_syncobj_get_stub_fence(void)
> +{
> +	spin_lock(&signaled_fence_lock);
> +	if (!signaled_fence.ops) {
> +		dma_fence_init(&signaled_fence,
> +			       &drm_syncobj_stub_fence_ops,
> +			       &signaled_fence_lock,
> +			       0, 0);
> +		dma_fence_signal_locked(&signaled_fence);
> +	}
> +	spin_unlock(&signaled_fence_lock);
> +
> +	return dma_fence_get(&signaled_fence);
> +}
>   /**
>    * drm_syncobj_find - lookup and reference a sync object.
>    * @file_private: drm file private pointer
> @@ -113,23 +130,8 @@ static struct dma_fence
>   	struct drm_syncobj_signal_pt *signal_pt;
>   
>   	if ((syncobj->type == DRM_SYNCOBJ_TYPE_TIMELINE) &&
> -	    (point <= syncobj->timeline)) {
> -		struct drm_syncobj_stub_fence *fence =
> -			kzalloc(sizeof(struct drm_syncobj_stub_fence),
> -				GFP_KERNEL);
> -
> -		if (!fence)
> -			return NULL;
> -		spin_lock_init(&fence->lock);
> -		dma_fence_init(&fence->base,
> -			       &drm_syncobj_stub_fence_ops,
> -			       &fence->lock,
> -			       syncobj->timeline_context,
> -			       point);
> -
> -		dma_fence_signal(&fence->base);
> -		return &fence->base;
> -	}
> +	    (point <= syncobj->timeline))
> +		return drm_syncobj_get_stub_fence();
>   
>   	list_for_each_entry(signal_pt, &syncobj->signal_pt_list, list) {
>   		if (point > signal_pt->value)