Commit 8f94eda3 authored by Christian König's avatar Christian König
Browse files

dma-buf: drop seq count based update 



This should be possible now since we don't have the distinction
between exclusive and shared fences any more.

The only possible pitfall is that a dma_fence would be reused during the
RCU grace period, but even that could be handled with a single extra check.

Signed-off-by: default avatarChristian König <christian.koenig@amd.com>
Reviewed-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220407085946.744568-15-christian.koenig@amd.com
parent 8bb31587

drivers/dma-buf/dma-resv.c

+12 −21
Original line number Diff line number Diff line
@@ -133,7 +133,6 @@ static void dma_resv_list_free(struct dma_resv_list *list) 
void dma_resv_init(struct dma_resv *obj)

{

	ww_mutex_init(&obj->lock, &reservation_ww_class);

	seqcount_ww_mutex_init(&obj->seq, &obj->lock);



	RCU_INIT_POINTER(obj->fences, NULL);

}
@@ -292,28 +291,24 @@ void dma_resv_add_fence(struct dma_resv *obj, struct dma_fence *fence, 
	fobj = dma_resv_fences_list(obj);

	count = fobj->num_fences;



	write_seqcount_begin(&obj->seq);



	for (i = 0; i < count; ++i) {

		enum dma_resv_usage old_usage;



		dma_resv_list_entry(fobj, i, obj, &old, &old_usage);

		if ((old->context == fence->context && old_usage >= usage) ||

		    dma_fence_is_signaled(old))

			goto replace;

		    dma_fence_is_signaled(old)) {

			dma_resv_list_set(fobj, i, fence, usage);

			dma_fence_put(old);

			return;

		}

	}



	BUG_ON(fobj->num_fences >= fobj->max_fences);

	old = NULL;

	count++;



replace:

	dma_resv_list_set(fobj, i, fence, usage);

	/* pointer update must be visible before we extend the num_fences */

	smp_store_mb(fobj->num_fences, count);



	write_seqcount_end(&obj->seq);

	dma_fence_put(old);

}

EXPORT_SYMBOL(dma_resv_add_fence);
@@ -341,7 +336,6 @@ void dma_resv_replace_fences(struct dma_resv *obj, uint64_t context, 
	dma_resv_assert_held(obj);



	list = dma_resv_fences_list(obj);

	write_seqcount_begin(&obj->seq);

	for (i = 0; list && i < list->num_fences; ++i) {

		struct dma_fence *old;
@@ -352,14 +346,12 @@ void dma_resv_replace_fences(struct dma_resv *obj, uint64_t context, 
		dma_resv_list_set(list, i, replacement, usage);

		dma_fence_put(old);

	}

	write_seqcount_end(&obj->seq);

}

EXPORT_SYMBOL(dma_resv_replace_fences);



/* Restart the unlocked iteration by initializing the cursor object. */

static void dma_resv_iter_restart_unlocked(struct dma_resv_iter *cursor)

{

	cursor->seq = read_seqcount_begin(&cursor->obj->seq);

	cursor->index = 0;

	cursor->num_fences = 0;

	cursor->fences = dma_resv_fences_list(cursor->obj);
@@ -388,8 +380,10 @@ static void dma_resv_iter_walk_unlocked(struct dma_resv_iter *cursor) 
				    cursor->obj, &cursor->fence,

				    &cursor->fence_usage);

		cursor->fence = dma_fence_get_rcu(cursor->fence);

		if (!cursor->fence)

			break;

		if (!cursor->fence) {

			dma_resv_iter_restart_unlocked(cursor);

			continue;

		}



		if (!dma_fence_is_signaled(cursor->fence) &&

		    cursor->usage >= cursor->fence_usage)
@@ -415,7 +409,7 @@ struct dma_fence *dma_resv_iter_first_unlocked(struct dma_resv_iter *cursor) 
	do {

		dma_resv_iter_restart_unlocked(cursor);

		dma_resv_iter_walk_unlocked(cursor);

	} while (read_seqcount_retry(&cursor->obj->seq, cursor->seq));

	} while (dma_resv_fences_list(cursor->obj) != cursor->fences);

	rcu_read_unlock();



	return cursor->fence;
@@ -438,13 +432,13 @@ struct dma_fence *dma_resv_iter_next_unlocked(struct dma_resv_iter *cursor) 


	rcu_read_lock();

	cursor->is_restarted = false;

	restart = read_seqcount_retry(&cursor->obj->seq, cursor->seq);

	restart = dma_resv_fences_list(cursor->obj) != cursor->fences;

	do {

		if (restart)

			dma_resv_iter_restart_unlocked(cursor);

		dma_resv_iter_walk_unlocked(cursor);

		restart = true;

	} while (read_seqcount_retry(&cursor->obj->seq, cursor->seq));

	} while (dma_resv_fences_list(cursor->obj) != cursor->fences);

	rcu_read_unlock();



	return cursor->fence;
@@ -540,10 +534,7 @@ int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src) 
	}

	dma_resv_iter_end(&cursor);



	write_seqcount_begin(&dst->seq);

	list = rcu_replace_pointer(dst->fences, list, dma_resv_held(dst));

	write_seqcount_end(&dst->seq);



	dma_resv_list_free(list);

	return 0;

}

drivers/dma-buf/st-dma-resv.c

+1 −1
Original line number Diff line number Diff line
@@ -217,7 +217,7 @@ static int test_for_each_unlocked(void *arg) 
		if (r == -ENOENT) {

			r = -EINVAL;

			/* That should trigger an restart */

			cursor.seq--;

			cursor.fences = (void*)~0;

		} else if (r == -EINVAL) {

			r = 0;

		}

include/linux/dma-resv.h

+0 −12
Original line number Diff line number Diff line
@@ -155,15 +155,6 @@ struct dma_resv { 
	 */

	struct ww_mutex lock;



	/**

	 * @seq:

	 *

	 * Sequence count for managing RCU read-side synchronization, allows

	 * read-only access to @fences while ensuring we take a consistent

	 * snapshot.

	 */

	seqcount_ww_mutex_t seq;



	/**

	 * @fences:

	 *
@@ -202,9 +193,6 @@ struct dma_resv_iter { 
	/** @fence_usage: the usage of the current fence */

	enum dma_resv_usage fence_usage;



	/** @seq: sequence number to check for modifications */

	unsigned int seq;



	/** @index: index into the shared fences */

	unsigned int index;