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* Deploying new iterator interface for dma-buf
@ 2021-09-16 11:30 ` Christian König
  0 siblings, 0 replies; 63+ messages in thread
From: Christian König @ 2021-09-16 11:30 UTC (permalink / raw)
  To: linaro-mm-sig, dri-devel, linux-media, intel-gfx; +Cc: daniel, tvrtko.ursulin

Next round for that one here, maybe the CI systems are now more
gracefully with me :)

I'm pretty sure that a couple of those dma_resv_for_each_fence_unlocked
should actually be replaced with lock+dma_resv_for_each_fence, but that
needs more auditing.

Please review and comment.

Thanks,
Christian.



^ permalink raw reply	[flat|nested] 63+ messages in thread
* Deploying new iterator interface for dma-buf
@ 2021-09-22  9:10 Christian König
  2021-09-22  9:10 ` [PATCH 06/26] dma-buf: use new iterator in dma_resv_test_signaled Christian König
  0 siblings, 1 reply; 63+ messages in thread
From: Christian König @ 2021-09-22  9:10 UTC (permalink / raw)
  To: linaro-mm-sig, dri-devel, linux-media, intel-gfx; +Cc: daniel, tvrtko.ursulin

Hi guys,

The version I've send out yesterday had a rather obvious coding error and I honestly forgot the cover letter.

This one here is better tested and will now hopefully not be torn apart from the CI system immediately.

I tried to address all review and documentation comments as best as I could, so I'm hoping that we can now considering pushing this.

Cheers,
Christian.



^ permalink raw reply	[flat|nested] 63+ messages in thread
* [PATCH 01/26] dma-buf: add dma_resv_for_each_fence_unlocked v3
@ 2021-09-21 17:36 Christian König
  2021-09-21 17:36 ` [PATCH 06/26] dma-buf: use new iterator in dma_resv_test_signaled Christian König
  0 siblings, 1 reply; 63+ messages in thread
From: Christian König @ 2021-09-21 17:36 UTC (permalink / raw)
  To: ckoenig.leichtzumerken, linaro-mm-sig, dri-devel, linux-media, intel-gfx
  Cc: daniel, tvrtko.ursulin

Abstract the complexity of iterating over all the fences
in a dma_resv object.

The new loop handles the whole RCU and retry dance and
returns only fences where we can be sure we grabbed the
right one.

v2: fix accessing the shared fences while they might be freed,
    improve kerneldoc, rename _cursor to _iter, add
    dma_resv_iter_is_exclusive, add dma_resv_iter_begin/end

v3: restructor the code, move rcu_read_lock()/unlock() into the
    iterator, add dma_resv_iter_is_restarted()

Signed-off-by: Christian König <christian.koenig@amd.com>
---
 drivers/dma-buf/dma-resv.c | 98 ++++++++++++++++++++++++++++++++++++++
 include/linux/dma-resv.h   | 95 ++++++++++++++++++++++++++++++++++++
 2 files changed, 193 insertions(+)

diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
index 84fbe60629e3..11b5399f4bd3 100644
--- a/drivers/dma-buf/dma-resv.c
+++ b/drivers/dma-buf/dma-resv.c
@@ -323,6 +323,104 @@ void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence)
 }
 EXPORT_SYMBOL(dma_resv_add_excl_fence);
 
+/**
+ * dma_resv_iter_restart_unlocked - restart the unlocked iterator
+ * @cursor: The dma_resv_iter object to restart
+ *
+ * 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 = -1;
+	if (cursor->all_fences) {
+		rcu_read_lock();
+		cursor->fences = dma_resv_shared_list(cursor->obj);
+		rcu_read_unlock();
+	} else {
+		cursor->fences = NULL;
+	}
+	cursor->is_restarted = true;
+}
+
+/**
+ * dma_resv_iter_walk_unlocked - walk over fences in a dma_resv obj
+ * @cursor: cursor to record the current position
+ *
+ * Return all the fences in the dma_resv object which are not yet signaled.
+ * The returned fence has an extra local reference so will stay alive.
+ * If a concurrent modify is detected the whole iterration is started over again.
+ */
+static void dma_resv_iter_walk_unlocked(struct dma_resv_iter *cursor)
+{
+	struct dma_resv *obj = cursor->obj;
+
+	do {
+		/* Drop the reference from the previous round */
+		dma_fence_put(cursor->fence);
+
+		if (cursor->index++ == -1) {
+			cursor->fence = dma_resv_excl_fence(obj);
+			cursor->fence = dma_fence_get_rcu(cursor->fence);
+
+		} else if (!cursor->fences ||
+			   cursor->index >= cursor->fences->shared_count) {
+			cursor->fence = NULL;
+
+		} else {
+			struct dma_resv_list *fences = cursor->fences;
+			unsigned int idx = cursor->index;
+
+			cursor->fence = rcu_dereference(fences->shared[idx]);
+			cursor->fence = dma_fence_get_rcu(cursor->fence);
+		}
+	} while (cursor->fence && dma_fence_is_signaled(cursor->fence));
+}
+
+/**
+ * dma_resv_iter_first_unlocked - first fence in an unlocked dma_resv obj.
+ * @cursor: the cursor with the current position
+ *
+ * Returns the first fence from an unlocked dma_resv obj.
+ */
+struct dma_fence *dma_resv_iter_first_unlocked(struct dma_resv_iter *cursor)
+{
+	rcu_read_lock();
+	do {
+		dma_resv_iter_restart_unlocked(cursor);
+		dma_resv_iter_walk_unlocked(cursor);
+	} while (read_seqcount_retry(&cursor->obj->seq, cursor->seq));
+	rcu_read_unlock();
+
+	return cursor->fence;
+}
+EXPORT_SYMBOL(dma_resv_iter_first_unlocked);
+
+/**
+ * dma_resv_iter_next_unlocked - next fence in an unlocked dma_resv obj.
+ * @cursor: the cursor with the current position
+ *
+ * Returns the next fence from an unlocked dma_resv obj.
+ */
+struct dma_fence *dma_resv_iter_next_unlocked(struct dma_resv_iter *cursor)
+{
+	bool restart;
+
+	rcu_read_lock();
+	cursor->is_restarted = false;
+	restart = read_seqcount_retry(&cursor->obj->seq, cursor->seq);
+	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));
+	rcu_read_unlock();
+
+	return cursor->fence;
+}
+EXPORT_SYMBOL(dma_resv_iter_next_unlocked);
+
 /**
  * dma_resv_copy_fences - Copy all fences from src to dst.
  * @dst: the destination reservation object
diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
index 9100dd3dc21f..baf77a542392 100644
--- a/include/linux/dma-resv.h
+++ b/include/linux/dma-resv.h
@@ -149,6 +149,101 @@ struct dma_resv {
 	struct dma_resv_list __rcu *fence;
 };
 
+/**
+ * struct dma_resv_iter - current position into the dma_resv fences
+ *
+ * Don't touch this directly in the driver, use the accessor function instead.
+ */
+struct dma_resv_iter {
+	/** @obj: The dma_resv object we iterate over */
+	struct dma_resv *obj;
+
+	/** @all_fences: If all fences should be returned */
+	bool all_fences;
+
+	/** @fence: the currently handled fence */
+	struct dma_fence *fence;
+
+	/** @seq: sequence number to check for modifications */
+	unsigned int seq;
+
+	/** @index: index into the shared fences */
+	unsigned int index;
+
+	/** @fences: the shared fences */
+	struct dma_resv_list *fences;
+
+	/** @is_restarted: true if this is the first returned fence */
+	bool is_restarted;
+};
+
+struct dma_fence *dma_resv_iter_first_unlocked(struct dma_resv_iter *cursor);
+struct dma_fence *dma_resv_iter_next_unlocked(struct dma_resv_iter *cursor);
+
+/**
+ * dma_resv_iter_begin - initialize a dma_resv_iter object
+ * @cursor: The dma_resv_iter object to initialize
+ * @obj: The dma_resv object which we want to iterator over
+ * @all_fences: If all fences should be returned or just the exclusive one
+ */
+static inline void dma_resv_iter_begin(struct dma_resv_iter *cursor,
+				       struct dma_resv *obj,
+				       bool all_fences)
+{
+	cursor->obj = obj;
+	cursor->all_fences = all_fences;
+	cursor->fence = NULL;
+}
+
+/**
+ * dma_resv_iter_end - cleanup a dma_resv_iter object
+ * @cursor: the dma_resv_iter object which should be cleaned up
+ *
+ * Make sure that the reference to the fence in the cursor is properly
+ * dropped.
+ */
+static inline void dma_resv_iter_end(struct dma_resv_iter *cursor)
+{
+	dma_fence_put(cursor->fence);
+}
+
+/**
+ * dma_resv_iter_is_exclusive - test if the current fence is the exclusive one
+ * @cursor: the cursor of the current position
+ *
+ * Returns true if the currently returned fence is the exclusive one.
+ */
+static inline bool dma_resv_iter_is_exclusive(struct dma_resv_iter *cursor)
+{
+	return cursor->index == -1;
+}
+
+/**
+ * dma_resv_iter_is_restarted - test if this is the first fence after a restart
+ * @cursor: the cursor with the current position
+ *
+ * Return true if this is the first fence in an interation after a restart.
+ */
+static inline bool dma_resv_iter_is_restarted(struct dma_resv_iter *cursor)
+{
+	return cursor->is_restarted;
+}
+
+/**
+ * dma_resv_for_each_fence_unlocked - unlocked fence iterator
+ * @cursor: a struct dma_resv_iter pointer
+ * @fence: the current fence
+ *
+ * Iterate over the fences in a struct dma_resv object without holding the
+ * &dma_resv.lock and using RCU instead. The cursor needs to be initialized
+ * with dma_resv_iter_begin() and cleaned up with dma_resv_iter_end(). Inside
+ * the iterator a reference to the dma_fence is hold and the RCU lock dropped.
+ * When the dma_resv is modified the iteration starts over again.
+ */
+#define dma_resv_for_each_fence_unlocked(cursor, fence)			\
+	for (fence = dma_resv_iter_first_unlocked(cursor);		\
+	     fence; fence = dma_resv_iter_next_unlocked(cursor))
+
 #define dma_resv_held(obj) lockdep_is_held(&(obj)->lock.base)
 #define dma_resv_assert_held(obj) lockdep_assert_held(&(obj)->lock.base)
 
-- 
2.25.1


^ permalink raw reply related	[flat|nested] 63+ messages in thread
* Deploying new iterator interface for dma-buf
@ 2021-09-17 12:34 Christian König
  2021-09-17 12:34 ` [PATCH 06/26] dma-buf: use new iterator in dma_resv_test_signaled Christian König
  0 siblings, 1 reply; 63+ messages in thread
From: Christian König @ 2021-09-17 12:34 UTC (permalink / raw)
  To: linaro-mm-sig, dri-devel, linux-media, intel-gfx; +Cc: daniel

Hopefully the last round for this.

Added dma_resv_iter_begin/end as requested by Daniel. Fixed a bunch of
problems pointed out by the CI systems and found a few more myselve.

Please review and/or comment,
Christian.



^ permalink raw reply	[flat|nested] 63+ messages in thread
* Deploying new iterator interface for dma-buf
@ 2021-09-13 13:16 Christian König
  2021-09-13 13:16 ` [PATCH 06/26] dma-buf: use new iterator in dma_resv_test_signaled Christian König
  0 siblings, 1 reply; 63+ messages in thread
From: Christian König @ 2021-09-13 13:16 UTC (permalink / raw)
  To: linaro-mm-sig, dri-devel, linux-media; +Cc: daniel, intel-gfx

Hi everybody,

we recently found that a good bunch of the RCU accesses to the dma_resv object are actually not correctly protected.

Those where fixed by either dropping the RCU approach and taking appropriate locks or using a central function to return the current fences as array and then work with that snapshot.

This set now tries to prevent adding any new broken code by rolling out two new interfaces to access the fences in a dma_resv object:

dma_resv_for_each_fence() - Iterator which should be used while holding the reservation lock.
dma_resv_for_each_fence_unlocked() - Iterator based on RCU which can be used without holding the reservation lock and automatic restart on concurrent modification.

While doing this we also move the decision which fences to use for write and read accesses into the dma_resv object which results in a quite nice code de-duplication and simplification.

The only two remaining users of the RCU shared fence interface are removing shared fences in amdkfd and debugfs code in qxl which will both be addresses in the next patch set.

Please review and/or comment,
Christian.



^ permalink raw reply	[flat|nested] 63+ messages in thread

end of thread, other threads:[~2021-09-22  9:10 UTC | newest]

Thread overview: 63+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-09-16 11:30 Deploying new iterator interface for dma-buf Christian König
2021-09-16 11:30 ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 01/26] dma-buf: add dma_resv_for_each_fence_unlocked v2 Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 12:15   ` Daniel Vetter
2021-09-16 12:15     ` [Intel-gfx] " Daniel Vetter
2021-09-16 11:30 ` [PATCH 02/26] dma-buf: add dma_resv_for_each_fence Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 03/26] dma-buf: use new iterator in dma_resv_copy_fences Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 04/26] dma-buf: use new iterator in dma_resv_get_fences v2 Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 05/26] dma-buf: use new iterator in dma_resv_wait_timeout Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 06/26] dma-buf: use new iterator in dma_resv_test_signaled Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 07/26] drm/ttm: use the new iterator in ttm_bo_flush_all_fences Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 08/26] drm/amdgpu: use the new iterator in amdgpu_sync_resv Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 09/26] drm/amdgpu: use new iterator in amdgpu_ttm_bo_eviction_valuable Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 10/26] drm/msm: use new iterator in msm_gem_describe Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 11/26] drm/radeon: use new iterator in radeon_sync_resv Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 12/26] drm/scheduler: use new iterator in drm_sched_job_add_implicit_dependencies v2 Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 13/26] drm/i915: use the new iterator in i915_gem_busy_ioctl Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 14/26] drm/i915: use the new iterator in i915_sw_fence_await_reservation v2 Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 15/26] drm/i915: use the new iterator in i915_request_await_object v2 Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 16/26] drm/i915: use new iterator in i915_gem_object_wait_reservation v2 Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 17/26] drm/i915: use new iterator in i915_gem_object_wait_priority v2 Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 18/26] drm/i915: use new iterator in i915_gem_object_last_write_engine v2 Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 19/26] drm/i915: use new cursor in intel_prepare_plane_fb v2 Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 20/26] drm: use new iterator in drm_gem_fence_array_add_implicit v2 Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 21/26] drm: use new iterator in drm_gem_plane_helper_prepare_fb v2 Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 22/26] drm/nouveau: use the new iterator in nouveau_fence_sync Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 23/26] drm/nouveau: use the new interator in nv50_wndw_prepare_fb v2 Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 24/26] drm/etnaviv: use new iterator in etnaviv_gem_describe Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 25/26] drm/etnaviv: replace dma_resv_get_excl_unlocked Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 11:30 ` [PATCH 26/26] dma-buf: nuke dma_resv_get_excl_unlocked Christian König
2021-09-16 11:30   ` [Intel-gfx] " Christian König
2021-09-16 12:28 ` [Intel-gfx] ✗ Fi.CI.CHECKPATCH: warning for series starting with [01/26] dma-buf: add dma_resv_for_each_fence_unlocked v2 Patchwork
2021-09-16 12:50 ` [Intel-gfx] ✗ Fi.CI.BAT: failure " Patchwork
  -- strict thread matches above, loose matches on Subject: below --
2021-09-22  9:10 Deploying new iterator interface for dma-buf Christian König
2021-09-22  9:10 ` [PATCH 06/26] dma-buf: use new iterator in dma_resv_test_signaled Christian König
2021-09-21 17:36 [PATCH 01/26] dma-buf: add dma_resv_for_each_fence_unlocked v3 Christian König
2021-09-21 17:36 ` [PATCH 06/26] dma-buf: use new iterator in dma_resv_test_signaled Christian König
2021-09-17 12:34 Deploying new iterator interface for dma-buf Christian König
2021-09-17 12:34 ` [PATCH 06/26] dma-buf: use new iterator in dma_resv_test_signaled Christian König
2021-09-17 14:45   ` Daniel Vetter
2021-09-13 13:16 Deploying new iterator interface for dma-buf Christian König
2021-09-13 13:16 ` [PATCH 06/26] dma-buf: use new iterator in dma_resv_test_signaled Christian König

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