On Fri, May 21, 2021 at 12:48 PM Daniel Vetter <daniel@xxxxxxxx> wrote:
>
> 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@xxxxxxxxxxxxxx>
> >
> > get_singleton
>
> Spurious thing here.
Fixed.
> > ---
> > 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.
Sure, I can write LESS documentation. :-P
> > +
> > 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.
Fixed.
> > + * @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
Done.
> 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.
I can make that change. I'll also include a patch in the next re-send
that renames all the _rcu helpers to _unlocked for consistency.
--Jason
> > + 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@xxxxxxxx>
>
> > +
> > /**
> > * 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
