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From: Daniel Vetter <daniel@ffwll.ch>
To: "Christian König" <ckoenig.leichtzumerken@gmail.com>
Cc: linaro-mm-sig@lists.linaro.org, dri-devel@lists.freedesktop.org,
	linux-media@vger.kernel.org, intel-gfx@lists.freedesktop.org,
	daniel@ffwll.ch, tvrtko.ursulin@linux.intel.com
Subject: Re: [PATCH 01/26] dma-buf: add dma_resv_for_each_fence_unlocked v2
Date: Thu, 16 Sep 2021 14:15:45 +0200	[thread overview]
Message-ID: <YUM1cY5HKixNUnQn@phenom.ffwll.local> (raw)
In-Reply-To: <20210916113042.3631-2-christian.koenig@amd.com>

On Thu, Sep 16, 2021 at 01:30:17PM +0200, Christian König wrote:
> 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
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>

Replied in the other thread with the fully typed out example, this really
needs iter_init/next/end here. Or it's just way too fragile and tricky for
a generic helper that we roll out everywhere.
-Daniel

> ---
>  drivers/dma-buf/dma-resv.c | 62 ++++++++++++++++++++++++++++++++++++++
>  include/linux/dma-resv.h   | 50 ++++++++++++++++++++++++++++++
>  2 files changed, 112 insertions(+)
> 
> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
> index 84fbe60629e3..77083170ec3b 100644
> --- a/drivers/dma-buf/dma-resv.c
> +++ b/drivers/dma-buf/dma-resv.c
> @@ -323,6 +323,68 @@ void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence)
>  }
>  EXPORT_SYMBOL(dma_resv_add_excl_fence);
>  
> +/**
> + * dma_resv_walk_unlocked - walk over fences in a dma_resv obj
> + * @obj: the dma_resv object
> + * @cursor: cursor to record the current position
> + * @all_fences: true returns also the shared fences
> + * @first: if we should start over
> + *
> + * 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 iterator is started over again.
> + */
> +struct dma_fence *dma_resv_walk_unlocked(struct dma_resv *obj,
> +					 struct dma_resv_iter *cursor,
> +					 bool all_fences, bool first)
> +{
> +	struct dma_fence *fence = NULL;
> +
> +	first |= read_seqcount_retry(&obj->seq, cursor->seq);
> +	do {
> +		/* Drop the reference from the previous round */
> +		dma_fence_put(fence);
> +
> +		cursor->is_first = first;
> +		if (first) {
> +			cursor->seq = read_seqcount_begin(&obj->seq);
> +			cursor->index = -1;
> +			cursor->fences = dma_resv_shared_list(obj);
> +
> +			fence = dma_resv_excl_fence(obj);
> +			if (fence && test_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
> +					      &fence->flags))
> +				fence = NULL;
> +		} else {
> +			fence = NULL;
> +		}
> +
> +		if (fence) {
> +			fence = dma_fence_get_rcu(fence);
> +		} else if (all_fences && cursor->fences) {
> +			struct dma_resv_list *fences = cursor->fences;
> +
> +			while (++cursor->index < fences->shared_count) {
> +				fence = rcu_dereference(
> +					fences->shared[cursor->index]);
> +				if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
> +					      &fence->flags))
> +					break;
> +			}
> +			if (cursor->index < fences->shared_count)
> +				fence = dma_fence_get_rcu(fence);
> +			else
> +				fence = NULL;
> +		}
> +
> +		/* For the eventually next round */
> +		first = true;
> +	} while (read_seqcount_retry(&obj->seq, cursor->seq));
> +
> +	return fence;
> +}
> +EXPORT_SYMBOL_GPL(dma_resv_walk_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..1cd686384c71 100644
> --- a/include/linux/dma-resv.h
> +++ b/include/linux/dma-resv.h
> @@ -149,6 +149,53 @@ 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 {
> +	/** @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_first: true if this is the first returned fence */
> +	bool is_first;
> +};
> +
> +/**
> + * dma_resv_for_each_fence_unlocked - fence iterator
> + * @obj: a dma_resv object pointer
> + * @cursor: a struct dma_resv_iter pointer
> + * @all_fences: true if all fences should be returned
> + * @fence: the current fence
> + *
> + * Iterate over the fences in a struct dma_resv object without holding the
> + * dma_resv::lock. The RCU read side lock must be hold when using this, but can
> + * be dropped and re-taken as necessary inside the loop. @all_fences controls
> + * if the shared fences are returned as well.
> + */
> +#define dma_resv_for_each_fence_unlocked(obj, cursor, all_fences, fence)    \
> +	for (fence = dma_resv_walk_unlocked(obj, cursor, all_fences, true); \
> +	     fence; dma_fence_put(fence),				    \
> +	     fence = dma_resv_walk_unlocked(obj, cursor, all_fences, false))
> +
> +/**
> + * 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;
> +}
> +
>  #define dma_resv_held(obj) lockdep_is_held(&(obj)->lock.base)
>  #define dma_resv_assert_held(obj) lockdep_assert_held(&(obj)->lock.base)
>  
> @@ -366,6 +413,9 @@ void dma_resv_fini(struct dma_resv *obj);
>  int dma_resv_reserve_shared(struct dma_resv *obj, unsigned int num_fences);
>  void dma_resv_add_shared_fence(struct dma_resv *obj, struct dma_fence *fence);
>  void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence);
> +struct dma_fence *dma_resv_walk_unlocked(struct dma_resv *obj,
> +					 struct dma_resv_iter *cursor,
> +					 bool first, bool all_fences);
>  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);
> -- 
> 2.25.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

WARNING: multiple messages have this Message-ID
From: Daniel Vetter <daniel@ffwll.ch>
To: "Christian König" <ckoenig.leichtzumerken@gmail.com>
Cc: linaro-mm-sig@lists.linaro.org, dri-devel@lists.freedesktop.org,
	linux-media@vger.kernel.org, intel-gfx@lists.freedesktop.org,
	daniel@ffwll.ch, tvrtko.ursulin@linux.intel.com
Subject: Re: [Intel-gfx] [PATCH 01/26] dma-buf: add dma_resv_for_each_fence_unlocked v2
Date: Thu, 16 Sep 2021 14:15:45 +0200	[thread overview]
Message-ID: <YUM1cY5HKixNUnQn@phenom.ffwll.local> (raw)
In-Reply-To: <20210916113042.3631-2-christian.koenig@amd.com>

On Thu, Sep 16, 2021 at 01:30:17PM +0200, Christian König wrote:
> 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
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>

Replied in the other thread with the fully typed out example, this really
needs iter_init/next/end here. Or it's just way too fragile and tricky for
a generic helper that we roll out everywhere.
-Daniel

> ---
>  drivers/dma-buf/dma-resv.c | 62 ++++++++++++++++++++++++++++++++++++++
>  include/linux/dma-resv.h   | 50 ++++++++++++++++++++++++++++++
>  2 files changed, 112 insertions(+)
> 
> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
> index 84fbe60629e3..77083170ec3b 100644
> --- a/drivers/dma-buf/dma-resv.c
> +++ b/drivers/dma-buf/dma-resv.c
> @@ -323,6 +323,68 @@ void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence)
>  }
>  EXPORT_SYMBOL(dma_resv_add_excl_fence);
>  
> +/**
> + * dma_resv_walk_unlocked - walk over fences in a dma_resv obj
> + * @obj: the dma_resv object
> + * @cursor: cursor to record the current position
> + * @all_fences: true returns also the shared fences
> + * @first: if we should start over
> + *
> + * 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 iterator is started over again.
> + */
> +struct dma_fence *dma_resv_walk_unlocked(struct dma_resv *obj,
> +					 struct dma_resv_iter *cursor,
> +					 bool all_fences, bool first)
> +{
> +	struct dma_fence *fence = NULL;
> +
> +	first |= read_seqcount_retry(&obj->seq, cursor->seq);
> +	do {
> +		/* Drop the reference from the previous round */
> +		dma_fence_put(fence);
> +
> +		cursor->is_first = first;
> +		if (first) {
> +			cursor->seq = read_seqcount_begin(&obj->seq);
> +			cursor->index = -1;
> +			cursor->fences = dma_resv_shared_list(obj);
> +
> +			fence = dma_resv_excl_fence(obj);
> +			if (fence && test_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
> +					      &fence->flags))
> +				fence = NULL;
> +		} else {
> +			fence = NULL;
> +		}
> +
> +		if (fence) {
> +			fence = dma_fence_get_rcu(fence);
> +		} else if (all_fences && cursor->fences) {
> +			struct dma_resv_list *fences = cursor->fences;
> +
> +			while (++cursor->index < fences->shared_count) {
> +				fence = rcu_dereference(
> +					fences->shared[cursor->index]);
> +				if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
> +					      &fence->flags))
> +					break;
> +			}
> +			if (cursor->index < fences->shared_count)
> +				fence = dma_fence_get_rcu(fence);
> +			else
> +				fence = NULL;
> +		}
> +
> +		/* For the eventually next round */
> +		first = true;
> +	} while (read_seqcount_retry(&obj->seq, cursor->seq));
> +
> +	return fence;
> +}
> +EXPORT_SYMBOL_GPL(dma_resv_walk_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..1cd686384c71 100644
> --- a/include/linux/dma-resv.h
> +++ b/include/linux/dma-resv.h
> @@ -149,6 +149,53 @@ 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 {
> +	/** @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_first: true if this is the first returned fence */
> +	bool is_first;
> +};
> +
> +/**
> + * dma_resv_for_each_fence_unlocked - fence iterator
> + * @obj: a dma_resv object pointer
> + * @cursor: a struct dma_resv_iter pointer
> + * @all_fences: true if all fences should be returned
> + * @fence: the current fence
> + *
> + * Iterate over the fences in a struct dma_resv object without holding the
> + * dma_resv::lock. The RCU read side lock must be hold when using this, but can
> + * be dropped and re-taken as necessary inside the loop. @all_fences controls
> + * if the shared fences are returned as well.
> + */
> +#define dma_resv_for_each_fence_unlocked(obj, cursor, all_fences, fence)    \
> +	for (fence = dma_resv_walk_unlocked(obj, cursor, all_fences, true); \
> +	     fence; dma_fence_put(fence),				    \
> +	     fence = dma_resv_walk_unlocked(obj, cursor, all_fences, false))
> +
> +/**
> + * 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;
> +}
> +
>  #define dma_resv_held(obj) lockdep_is_held(&(obj)->lock.base)
>  #define dma_resv_assert_held(obj) lockdep_assert_held(&(obj)->lock.base)
>  
> @@ -366,6 +413,9 @@ void dma_resv_fini(struct dma_resv *obj);
>  int dma_resv_reserve_shared(struct dma_resv *obj, unsigned int num_fences);
>  void dma_resv_add_shared_fence(struct dma_resv *obj, struct dma_fence *fence);
>  void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence);
> +struct dma_fence *dma_resv_walk_unlocked(struct dma_resv *obj,
> +					 struct dma_resv_iter *cursor,
> +					 bool first, bool all_fences);
>  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);
> -- 
> 2.25.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

  reply	other threads:[~2021-09-16 12:15 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
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 [this message]
2021-09-16 12:15     ` 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
2021-09-17 12:34 Deploying new iterator interface for dma-buf Christian König
2021-09-17 12:34 ` [PATCH 01/26] dma-buf: add dma_resv_for_each_fence_unlocked v2 Christian König
2021-09-17 13:23   ` Daniel Vetter

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