Re: [PATCH 2/6] dma-buf: Add dma_resv_get_singleton (v6)

["Christian König" <christian.koenig@amd.com>]

Am 10.06.21 um 23:09 schrieb Jason Ekstrand:
> Add a helper function to get a single fence representing
> all fences in a dma_resv object.
>
> This fence is either the only one in the object or all not
> signaled fences of the object in a flatted out dma_fence_array.
>
> v2 (Jason Ekstrand):
>   - Take reference of fences both for creating the dma_fence_array and in
>     the case where we return one fence.
>   - Handle the case where dma_resv_get_list() returns NULL
>
> v3 (Jason Ekstrand):
>   - Add an _rcu suffix because it is read-only
>   - Rewrite to use dma_resv_get_fences_rcu so it's RCU-safe
>   - Add an EXPORT_SYMBOL_GPL declaration
>   - Re-author the patch to Jason since very little is left of Christian
>     König's original patch
>   - Remove the extra fence argument
>
> v4 (Jason Ekstrand):
>   - Restore the extra fence argument
>
> v5 (Daniel Vetter):
>   - Rename from _rcu to _unlocked since it doesn't leak RCU details to
>     the caller
>   - Fix docs
>   - Use ERR_PTR for error handling rather than an output dma_fence**
>
> v5 (Jason Ekstrand):
>   - Drop the extra fence param and leave that to a separate patch
>
> v6 (Jason Ekstrand):
>   - Rename to dma_resv_get_singleton to match the new naming convention
>     for dma_resv helpers which work without taking a lock.
>
> Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

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

> Cc: Christian König <christian.koenig@amd.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> ---
>   drivers/dma-buf/dma-resv.c | 91 ++++++++++++++++++++++++++++++++++++++
>   include/linux/dma-resv.h   |  1 +
>   2 files changed, 92 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
> index f26c71747d43a..1b26aa7e5d81c 100644
> --- a/drivers/dma-buf/dma-resv.c
> +++ b/drivers/dma-buf/dma-resv.c
> @@ -34,6 +34,8 @@
>    */
>   
>   #include <linux/dma-resv.h>
> +#include <linux/dma-fence-chain.h>
> +#include <linux/dma-fence-array.h>
>   #include <linux/export.h>
>   #include <linux/mm.h>
>   #include <linux/sched/mm.h>
> @@ -50,6 +52,10 @@
>    * write-side updates.
>    */
>   
> +#define dma_fence_deep_dive_for_each(fence, chain, index, head)	\
> +	dma_fence_chain_for_each(chain, head)			\
> +		dma_fence_array_for_each(fence, index, chain)
> +
>   DEFINE_WD_CLASS(reservation_ww_class);
>   EXPORT_SYMBOL(reservation_ww_class);
>   
> @@ -495,6 +501,91 @@ int dma_resv_get_fences(struct dma_resv *obj, struct dma_fence **pfence_excl,
>   }
>   EXPORT_SYMBOL_GPL(dma_resv_get_fences);
>   
> +/**
> + * dma_resv_get_singleton - get a single fence for the dma_resv object
> + * @obj: the reservation object
> + *
> + * Get a single fence representing all unsignaled fences in the dma_resv object
> + * plus the given extra fence. If we got only one fence return a new
> + * reference to that, otherwise return a dma_fence_array object.
> + *
> + * RETURNS
> + * The singleton dma_fence on success or an ERR_PTR on failure
> + */
> +struct dma_fence *dma_resv_get_singleton(struct dma_resv *obj)
> +{
> +	struct dma_fence *result, **resv_fences, *fence, *chain, **fences;
> +	struct dma_fence_array *array;
> +	unsigned int num_resv_fences, num_fences;
> +	unsigned int err, i, j;
> +
> +	err = dma_resv_get_fences(obj, NULL, &num_resv_fences, &resv_fences);
> +	if (err)
> +		return ERR_PTR(err);
> +
> +	if (num_resv_fences == 0)
> +		return NULL;
> +
> +	num_fences = 0;
> +	result = NULL;
> +
> +	for (i = 0; i < num_resv_fences; ++i) {
> +		dma_fence_deep_dive_for_each(fence, chain, j, resv_fences[i]) {
> +			if (dma_fence_is_signaled(fence))
> +				continue;
> +
> +			result = fence;
> +			++num_fences;
> +		}
> +	}
> +
> +	if (num_fences <= 1) {
> +		result = dma_fence_get(result);
> +		goto put_resv_fences;
> +	}
> +
> +	fences = kmalloc_array(num_fences, sizeof(struct dma_fence *),
> +			       GFP_KERNEL);
> +	if (!fences) {
> +		result = ERR_PTR(-ENOMEM);
> +		goto put_resv_fences;
> +	}
> +
> +	num_fences = 0;
> +	for (i = 0; i < num_resv_fences; ++i) {
> +		dma_fence_deep_dive_for_each(fence, chain, j, resv_fences[i]) {
> +			if (!dma_fence_is_signaled(fence))
> +				fences[num_fences++] = dma_fence_get(fence);
> +		}
> +	}
> +
> +	if (num_fences <= 1) {
> +		result = num_fences ? fences[0] : NULL;
> +		kfree(fences);
> +		goto put_resv_fences;
> +	}
> +
> +	array = dma_fence_array_create(num_fences, fences,
> +				       dma_fence_context_alloc(1),
> +				       1, false);
> +	if (array) {
> +		result = &array->base;
> +	} else {
> +		result = ERR_PTR(-ENOMEM);
> +		while (num_fences--)
> +			dma_fence_put(fences[num_fences]);
> +		kfree(fences);
> +	}
> +
> +put_resv_fences:
> +	while (num_resv_fences--)
> +		dma_fence_put(resv_fences[num_resv_fences]);
> +	kfree(resv_fences);
> +
> +	return result;
> +}
> +EXPORT_SYMBOL_GPL(dma_resv_get_singleton);
> +
>   /**
>    * dma_resv_wait_timeout - Wait on reservation's objects
>    * shared and/or exclusive fences.
> diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
> index 562b885cf9c3d..d60982975a786 100644
> --- a/include/linux/dma-resv.h
> +++ b/include/linux/dma-resv.h
> @@ -275,6 +275,7 @@ void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence);
>   int dma_resv_get_fences(struct dma_resv *obj, struct dma_fence **pfence_excl,
>   			unsigned *pshared_count, struct dma_fence ***pshared);
>   int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src);
> +struct dma_fence *dma_resv_get_singleton(struct dma_resv *obj);
>   long dma_resv_wait_timeout(struct dma_resv *obj, bool wait_all, bool intr,
>   			   unsigned long timeout);
>   bool dma_resv_test_signaled(struct dma_resv *obj, bool test_all);