[PATCH 2/4] dma-buf: add dma_resv_get_singleton_rcu (v4)
Daniel Vetter
daniel at ffwll.ch
Fri May 21 17:48:42 UTC 2021
On Thu, May 20, 2021 at 02:00:05PM -0500, Jason Ekstrand wrote:
> 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
>
> Signed-off-by: Jason Ekstrand <jason at jlekstrand.net>
>
> get_singleton
Spurious thing here.
> ---
> drivers/dma-buf/dma-resv.c | 122 +++++++++++++++++++++++++++++++++++++
> include/linux/dma-resv.h | 3 +
> 2 files changed, 125 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
> index 6ddbeb5dfbf65..25995fc15c370 100644
> --- a/drivers/dma-buf/dma-resv.c
> +++ b/drivers/dma-buf/dma-resv.c
> @@ -33,6 +33,8 @@
> */
>
> #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>
> @@ -49,6 +51,19 @@
> * write-side updates.
> */
>
> +/**
> + * dma_fence_deep_dive_for_each - deep dive into the fence containers
> + * @fence: resulting fence
> + * @chain: variable for a dma_fence_chain
> + * @index: index into a dma_fence_array
> + * @head: starting point
> + *
> + * Helper to deep dive into the fence containers for flattening them.
> + */
> +#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)
Since this is is just internal helper in the .c file we generally don't
document it. Maybe small comment if you feel it's worth it.
> +
> DEFINE_WD_CLASS(reservation_ww_class);
> EXPORT_SYMBOL(reservation_ww_class);
>
> @@ -517,6 +532,113 @@ int dma_resv_get_fences_rcu(struct dma_resv *obj,
> }
> EXPORT_SYMBOL_GPL(dma_resv_get_fences_rcu);
>
> +/**
> + * dma_resv_get_singleton - get a single fence for the dma_resv object
Name doesn't match here.
> + * @obj: the reservation object
> + * @extra: extra fence to add to the resulting array
> + * @result: resulting dma_fence
> + *
> + * 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
> + * Returns -NOMEM if allocations fail, zero otherwise.
Kernel often encodes this in ERR_PTR so that you don't have to pass a
pointer to store the result. Would feel more kerenl-y I think that way. So
no result parameter, and on alloc failure you'd return
return ERR_PTR(-ENOMEM);
> + */
> +int dma_resv_get_singleton_rcu(struct dma_resv *obj, struct dma_fence *extra,
tbh the _rcu here is confusing. I think _unlocked is the better suffix,
maybe we should rename dma_resv_get_fences_rcu too for consistency. The
rcu-ness of the lookup isn't leaked to callers at all, so no point giving
them a panic.
> + struct dma_fence **result)
> +{
> + struct dma_fence **resv_fences, *fence, *chain, **fences;
> + struct dma_fence_array *array;
> + unsigned int num_resv_fences, num_fences;
> + unsigned int ret, i, j;
> +
> + ret = dma_resv_get_fences_rcu(obj, NULL, &num_resv_fences, &resv_fences);
> + if (ret)
> + return ret;
> +
> + num_fences = 0;
> + *result = NULL;
> +
> + if (num_resv_fences == 0 && !extra)
> + return 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))
> + continue;
> +
> + *result = fence;
> + ++num_fences;
> + }
> + }
> +
> + if (extra) {
> + dma_fence_deep_dive_for_each(fence, chain, j, extra) {
> + 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 = NULL;
> + ret = -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 (extra) {
> + dma_fence_deep_dive_for_each(fence, chain, j, extra) {
> + 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 = NULL;
> + while (num_fences--)
> + dma_fence_put(fences[num_fences]);
> + kfree(fences);
> + ret = -ENOMEM;
> + }
> +
> +put_resv_fences:
> + while (num_resv_fences--)
> + dma_fence_put(resv_fences[num_resv_fences]);
> + kfree(resv_fences);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(dma_resv_get_singleton_rcu);
With the nits addressed:
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> +
> /**
> * dma_resv_wait_timeout_rcu - 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 d44a77e8a7e34..d49ca263e78b4 100644
> --- a/include/linux/dma-resv.h
> +++ b/include/linux/dma-resv.h
> @@ -285,6 +285,9 @@ int dma_resv_get_fences_rcu(struct dma_resv *obj,
>
> int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src);
>
> +int dma_resv_get_singleton_rcu(struct dma_resv *obj, struct dma_fence *extra,
> + struct dma_fence **result);
> +
> long dma_resv_wait_timeout_rcu(struct dma_resv *obj, bool wait_all, bool intr,
> unsigned long timeout);
>
> --
> 2.31.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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