On 30-11-2021 13:19, Thomas Hellström wrote:
> The locking order for taking two fence locks is implicitly defined in
> at least two ways in the code:
>
> 1) Fence containers first and other fences next, which is defined by
> the enable_signaling() callbacks of dma_fence_chain and
> dma_fence_array.
> 2) Reverse signal order, which is used by __i915_active_fence_set().
>
> Now 1) implies 2), except for the signal_on_any mode of dma_fence_array
> and 2) does not imply 1), and also 1) makes locking order between
> different containers confusing.
>
> Establish 2) and fix up the signal_on_any mode by calling
> enable_signaling() on such fences unlocked at creation.
>
> Cc: linaro-mm-sig@xxxxxxxxxxxxxxxx
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: Christian König <christian.koenig@xxxxxxx>
> Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> ---
> drivers/dma-buf/dma-fence-array.c | 13 +++--
> drivers/dma-buf/dma-fence-chain.c | 3 +-
> drivers/dma-buf/dma-fence.c | 79 +++++++++++++++++++++----------
> include/linux/dma-fence.h | 3 ++
> 4 files changed, 69 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c
> index 3e07f961e2f3..0322b92909fe 100644
> --- a/drivers/dma-buf/dma-fence-array.c
> +++ b/drivers/dma-buf/dma-fence-array.c
> @@ -84,8 +84,8 @@ static bool dma_fence_array_enable_signaling(struct dma_fence *fence)
> * insufficient).
> */
> dma_fence_get(&array->base);
> - if (dma_fence_add_callback(array->fences[i], &cb[i].cb,
> - dma_fence_array_cb_func)) {
> + if (dma_fence_add_callback_nested(array->fences[i], &cb[i].cb,
> + dma_fence_array_cb_func)) {
> int error = array->fences[i]->error;
>
> dma_fence_array_set_pending_error(array, error);
> @@ -158,6 +158,7 @@ struct dma_fence_array *dma_fence_array_create(int num_fences,
> {
> struct dma_fence_array *array;
> size_t size = sizeof(*array);
> + struct dma_fence *fence;
>
> /* Allocate the callback structures behind the array. */
> size += num_fences * sizeof(struct dma_fence_array_cb);
> @@ -165,8 +166,9 @@ struct dma_fence_array *dma_fence_array_create(int num_fences,
> if (!array)
> return NULL;
>
> + fence = &array->base;
> spin_lock_init(&array->lock);
> - dma_fence_init(&array->base, &dma_fence_array_ops, &array->lock,
> + dma_fence_init(fence, &dma_fence_array_ops, &array->lock,
> context, seqno);
> init_irq_work(&array->work, irq_dma_fence_array_work);
>
> @@ -174,7 +176,10 @@ struct dma_fence_array *dma_fence_array_create(int num_fences,
> atomic_set(&array->num_pending, signal_on_any ? 1 : num_fences);
> array->fences = fences;
>
> - array->base.error = PENDING_ERROR;
> + fence->error = PENDING_ERROR;
> +
> + if (signal_on_any)
> + dma_fence_enable_sw_signaling(fence);
>
> return array;
> }
> diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c
> index 1b4cb3e5cec9..0518e53880f6 100644
> --- a/drivers/dma-buf/dma-fence-chain.c
> +++ b/drivers/dma-buf/dma-fence-chain.c
> @@ -152,7 +152,8 @@ static bool dma_fence_chain_enable_signaling(struct dma_fence *fence)
> struct dma_fence *f = chain ? chain->fence : fence;
>
> dma_fence_get(f);
> - if (!dma_fence_add_callback(f, &head->cb, dma_fence_chain_cb)) {
> + if (!dma_fence_add_callback_nested(f, &head->cb,
> + dma_fence_chain_cb)) {
> dma_fence_put(fence);
> return true;
> }
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index 066400ed8841..90a3d5121746 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -610,6 +610,37 @@ void dma_fence_enable_sw_signaling(struct dma_fence *fence)
> }
> EXPORT_SYMBOL(dma_fence_enable_sw_signaling);
>
> +static int __dma_fence_add_callback(struct dma_fence *fence,
> + struct dma_fence_cb *cb,
> + dma_fence_func_t func,
> + int nest_level)
> +{
> + unsigned long flags;
> + int ret = 0;
> +
> + if (WARN_ON(!fence || !func))
> + return -EINVAL;
> +
> + if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
> + INIT_LIST_HEAD(&cb->node);
> + return -ENOENT;
> + }
> +
> + spin_lock_irqsave_nested(fence->lock, flags, 0);
Forgot to hook up nest_level here?
> +
> + if (__dma_fence_enable_signaling(fence)) {
> + cb->func = func;
> + list_add_tail(&cb->node, &fence->cb_list);
> + } else {
> + INIT_LIST_HEAD(&cb->node);
> + ret = -ENOENT;
> + }
> +
> + spin_unlock_irqrestore(fence->lock, flags);
> +
> + return ret;
> +}
> +
> /**
> * dma_fence_add_callback - add a callback to be called when the fence
> * is signaled
> @@ -635,33 +666,33 @@ EXPORT_SYMBOL(dma_fence_enable_sw_signaling);
> int dma_fence_add_callback(struct dma_fence *fence, struct dma_fence_cb *cb,
> dma_fence_func_t func)
> {
> - unsigned long flags;
> - int ret = 0;
> -
> - if (WARN_ON(!fence || !func))
> - return -EINVAL;
> -
> - if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
> - INIT_LIST_HEAD(&cb->node);
> - return -ENOENT;
> - }
> -
> - spin_lock_irqsave(fence->lock, flags);
> -
> - if (__dma_fence_enable_signaling(fence)) {
> - cb->func = func;
> - list_add_tail(&cb->node, &fence->cb_list);
> - } else {
> - INIT_LIST_HEAD(&cb->node);
> - ret = -ENOENT;
> - }
> -
> - spin_unlock_irqrestore(fence->lock, flags);
> -
> - return ret;
> + return __dma_fence_add_callback(fence, cb, func, 0);
> }
> EXPORT_SYMBOL(dma_fence_add_callback);
>
Other than that, I didn't investigate the nesting fails enough to say I can accurately review this. :)
~Maarten
