Re: [PATCH v3 5/9] dma-buf: Move dma_buf_mmap_unlocked() to dynamic locking specification

Re: [PATCH v3 5/9] dma-buf: Move dma_buf_mmap_unlocked() to dynamic locking specification

[Christian König via Virtualization]

This should work, but I'm really wondering if this makes a difference 
for somebody.

Anyway the approach is fine with me: Acked-by: Christian König 
<christian.koenig@amd.com>

Regards,
Christian.

Am 24.08.22 um 12:22 schrieb Dmitry Osipenko:
> Move dma_buf_mmap_unlocked() function to the dynamic locking specification
> by taking the reservation lock. Neither of the today's drivers take the
> reservation lock within the mmap() callback, hence it's safe to enforce
> the locking.
>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> ---
>   drivers/dma-buf/dma-buf.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index f358af401360..4556a12bd741 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -1348,6 +1348,8 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_end_cpu_access, DMA_BUF);
>   int dma_buf_mmap_unlocked(struct dma_buf *dmabuf, struct vm_area_struct *vma,
>   			  unsigned long pgoff)
>   {
> +	int ret;
> +
>   	if (WARN_ON(!dmabuf || !vma))
>   		return -EINVAL;
>   
> @@ -1368,7 +1370,11 @@ int dma_buf_mmap_unlocked(struct dma_buf *dmabuf, struct vm_area_struct *vma,
>   	vma_set_file(vma, dmabuf->file);
>   	vma->vm_pgoff = pgoff;
>   
> -	return dmabuf->ops->mmap(dmabuf, vma);
> +	dma_resv_lock(dmabuf->resv, NULL);
> +	ret = dmabuf->ops->mmap(dmabuf, vma);
> +	dma_resv_unlock(dmabuf->resv);
> +
> +	return ret;
>   }
>   EXPORT_SYMBOL_NS_GPL(dma_buf_mmap_unlocked, DMA_BUF);
>   

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Re: [PATCH v3 6/9] dma-buf: Move dma-buf attachment to dynamic locking specification

[Christian König via Virtualization]

Am 24.08.22 um 12:22 schrieb Dmitry Osipenko:
> Move dma-buf attachment API functions to the dynamic locking specification.
> The strict locking convention prevents deadlock situations for dma-buf
> importers and exporters.
>
> Previously, the "unlocked" versions of the attachment API functions
> weren't taking the reservation lock and this patch makes them to take
> the lock.

Didn't we concluded that we need to keep the attach and detach callbacks 
without the lock and only move the map/unmap callbacks over?

Otherwise it won't be possible for drivers to lock multiple buffers if 
they have to shuffle things around for a specific attachment.

Regards,
Christian.

>
> Intel and AMD GPU drivers already were mapping the attached dma-bufs under
> the held lock during attachment, hence these drivers are updated to use
> the locked functions.
>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> ---
>   drivers/dma-buf/dma-buf.c                  | 115 ++++++++++++++-------
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c    |   4 +-
>   drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c |   8 +-
>   drivers/gpu/drm/i915/gem/i915_gem_object.c |  12 +++
>   include/linux/dma-buf.h                    |  20 ++--
>   5 files changed, 110 insertions(+), 49 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 4556a12bd741..f2a5a122da4a 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -559,7 +559,7 @@ static struct file *dma_buf_getfile(struct dma_buf *dmabuf, int flags)
>    * 2. Userspace passes this file-descriptors to all drivers it wants this buffer
>    *    to share with: First the file descriptor is converted to a &dma_buf using
>    *    dma_buf_get(). Then the buffer is attached to the device using
> - *    dma_buf_attach().
> + *    dma_buf_attach_unlocked().
>    *
>    *    Up to this stage the exporter is still free to migrate or reallocate the
>    *    backing storage.
> @@ -569,8 +569,8 @@ static struct file *dma_buf_getfile(struct dma_buf *dmabuf, int flags)
>    *    dma_buf_map_attachment() and dma_buf_unmap_attachment().
>    *
>    * 4. Once a driver is done with a shared buffer it needs to call
> - *    dma_buf_detach() (after cleaning up any mappings) and then release the
> - *    reference acquired with dma_buf_get() by calling dma_buf_put().
> + *    dma_buf_detach_unlocked() (after cleaning up any mappings) and then
> + *    release the reference acquired with dma_buf_get() by calling dma_buf_put().
>    *
>    * For the detailed semantics exporters are expected to implement see
>    * &dma_buf_ops.
> @@ -802,7 +802,7 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
>    * @importer_priv:	[in]	importer private pointer for the attachment
>    *
>    * Returns struct dma_buf_attachment pointer for this attachment. Attachments
> - * must be cleaned up by calling dma_buf_detach().
> + * must be cleaned up by calling dma_buf_detach_unlocked().
>    *
>    * Optionally this calls &dma_buf_ops.attach to allow device-specific attach
>    * functionality.
> @@ -858,8 +858,8 @@ dma_buf_dynamic_attach_unlocked(struct dma_buf *dmabuf, struct device *dev,
>   	    dma_buf_is_dynamic(dmabuf)) {
>   		struct sg_table *sgt;
>   
> +		dma_resv_lock(attach->dmabuf->resv, NULL);
>   		if (dma_buf_is_dynamic(attach->dmabuf)) {
> -			dma_resv_lock(attach->dmabuf->resv, NULL);
>   			ret = dmabuf->ops->pin(attach);
>   			if (ret)
>   				goto err_unlock;
> @@ -872,8 +872,7 @@ dma_buf_dynamic_attach_unlocked(struct dma_buf *dmabuf, struct device *dev,
>   			ret = PTR_ERR(sgt);
>   			goto err_unpin;
>   		}
> -		if (dma_buf_is_dynamic(attach->dmabuf))
> -			dma_resv_unlock(attach->dmabuf->resv);
> +		dma_resv_unlock(attach->dmabuf->resv);
>   		attach->sgt = sgt;
>   		attach->dir = DMA_BIDIRECTIONAL;
>   	}
> @@ -889,8 +888,7 @@ dma_buf_dynamic_attach_unlocked(struct dma_buf *dmabuf, struct device *dev,
>   		dmabuf->ops->unpin(attach);
>   
>   err_unlock:
> -	if (dma_buf_is_dynamic(attach->dmabuf))
> -		dma_resv_unlock(attach->dmabuf->resv);
> +	dma_resv_unlock(attach->dmabuf->resv);
>   
>   	dma_buf_detach_unlocked(dmabuf, attach);
>   	return ERR_PTR(ret);
> @@ -927,7 +925,7 @@ static void __unmap_dma_buf(struct dma_buf_attachment *attach,
>    * @dmabuf:	[in]	buffer to detach from.
>    * @attach:	[in]	attachment to be detached; is free'd after this call.
>    *
> - * Clean up a device attachment obtained by calling dma_buf_attach().
> + * Clean up a device attachment obtained by calling dma_buf_attach_unlocked().
>    *
>    * Optionally this calls &dma_buf_ops.detach for device-specific detach.
>    */
> @@ -937,21 +935,19 @@ void dma_buf_detach_unlocked(struct dma_buf *dmabuf,
>   	if (WARN_ON(!dmabuf || !attach))
>   		return;
>   
> +	dma_resv_lock(attach->dmabuf->resv, NULL);
> +
>   	if (attach->sgt) {
> -		if (dma_buf_is_dynamic(attach->dmabuf))
> -			dma_resv_lock(attach->dmabuf->resv, NULL);
>   
>   		__unmap_dma_buf(attach, attach->sgt, attach->dir);
>   
> -		if (dma_buf_is_dynamic(attach->dmabuf)) {
> +		if (dma_buf_is_dynamic(attach->dmabuf))
>   			dmabuf->ops->unpin(attach);
> -			dma_resv_unlock(attach->dmabuf->resv);
> -		}
>   	}
> -
> -	dma_resv_lock(dmabuf->resv, NULL);
>   	list_del(&attach->node);
> +
>   	dma_resv_unlock(dmabuf->resv);
> +
>   	if (dmabuf->ops->detach)
>   		dmabuf->ops->detach(dmabuf, attach);
>   
> @@ -1011,7 +1007,7 @@ void dma_buf_unpin(struct dma_buf_attachment *attach)
>   EXPORT_SYMBOL_NS_GPL(dma_buf_unpin, DMA_BUF);
>   
>   /**
> - * dma_buf_map_attachment_unlocked - Returns the scatterlist table of the attachment;
> + * dma_buf_map_attachment - Returns the scatterlist table of the attachment;
>    * mapped into _device_ address space. Is a wrapper for map_dma_buf() of the
>    * dma_buf_ops.
>    * @attach:	[in]	attachment whose scatterlist is to be returned
> @@ -1030,10 +1026,11 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_unpin, DMA_BUF);
>    *
>    * Important: Dynamic importers must wait for the exclusive fence of the struct
>    * dma_resv attached to the DMA-BUF first.
> + *
> + * Importer is responsible for holding dmabuf's reservation lock.
>    */
> -struct sg_table *
> -dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach,
> -				enum dma_data_direction direction)
> +struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
> +					enum dma_data_direction direction)
>   {
>   	struct sg_table *sg_table;
>   	int r;
> @@ -1043,8 +1040,7 @@ dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach,
>   	if (WARN_ON(!attach || !attach->dmabuf))
>   		return ERR_PTR(-EINVAL);
>   
> -	if (dma_buf_attachment_is_dynamic(attach))
> -		dma_resv_assert_held(attach->dmabuf->resv);
> +	dma_resv_assert_held(attach->dmabuf->resv);
>   
>   	if (attach->sgt) {
>   		/*
> @@ -1059,7 +1055,6 @@ dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach,
>   	}
>   
>   	if (dma_buf_is_dynamic(attach->dmabuf)) {
> -		dma_resv_assert_held(attach->dmabuf->resv);
>   		if (!IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY)) {
>   			r = attach->dmabuf->ops->pin(attach);
>   			if (r)
> @@ -1099,10 +1094,38 @@ dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach,
>   #endif /* CONFIG_DMA_API_DEBUG */
>   	return sg_table;
>   }
> +EXPORT_SYMBOL_NS_GPL(dma_buf_map_attachment, DMA_BUF);
> +
> +/**
> + * dma_buf_map_attachment_unlocked - Returns the scatterlist table of the attachment;
> + * mapped into _device_ address space. Is a wrapper for map_dma_buf() of the
> + * dma_buf_ops.
> + * @attach:	[in]	attachment whose scatterlist is to be returned
> + * @direction:	[in]	direction of DMA transfer
> + *
> + * Unlocked variant of dma_buf_map_attachment().
> + */
> +struct sg_table *
> +dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach,
> +				enum dma_data_direction direction)
> +{
> +	struct sg_table *sg_table;
> +
> +	might_sleep();
> +
> +	if (WARN_ON(!attach || !attach->dmabuf))
> +		return ERR_PTR(-EINVAL);
> +
> +	dma_resv_lock(attach->dmabuf->resv, NULL);
> +	sg_table = dma_buf_map_attachment(attach, direction);
> +	dma_resv_unlock(attach->dmabuf->resv);
> +
> +	return sg_table;
> +}
>   EXPORT_SYMBOL_NS_GPL(dma_buf_map_attachment_unlocked, DMA_BUF);
>   
>   /**
> - * dma_buf_unmap_attachment_unlocked - unmaps and decreases usecount of the buffer;might
> + * dma_buf_unmap_attachment - unmaps and decreases usecount of the buffer;might
>    * deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf() of
>    * dma_buf_ops.
>    * @attach:	[in]	attachment to unmap buffer from
> @@ -1110,31 +1133,51 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_map_attachment_unlocked, DMA_BUF);
>    * @direction:  [in]    direction of DMA transfer
>    *
>    * This unmaps a DMA mapping for @attached obtained by dma_buf_map_attachment().
> + *
> + * Importer is responsible for holding dmabuf's reservation lock.
>    */
> -void dma_buf_unmap_attachment_unlocked(struct dma_buf_attachment *attach,
> -				       struct sg_table *sg_table,
> -				       enum dma_data_direction direction)
> +void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
> +			      struct sg_table *sg_table,
> +			      enum dma_data_direction direction)
>   {
>   	might_sleep();
>   
> -	if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
> -		return;
> -
> -	if (dma_buf_attachment_is_dynamic(attach))
> -		dma_resv_assert_held(attach->dmabuf->resv);
> +	dma_resv_assert_held(attach->dmabuf->resv);
>   
>   	if (attach->sgt == sg_table)
>   		return;
>   
> -	if (dma_buf_is_dynamic(attach->dmabuf))
> -		dma_resv_assert_held(attach->dmabuf->resv);
> -
>   	__unmap_dma_buf(attach, sg_table, direction);
>   
>   	if (dma_buf_is_dynamic(attach->dmabuf) &&
>   	    !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))
>   		dma_buf_unpin(attach);
>   }
> +EXPORT_SYMBOL_NS_GPL(dma_buf_unmap_attachment, DMA_BUF);
> +
> +/**
> + * dma_buf_unmap_attachment_unlocked - unmaps and decreases usecount of the buffer;might
> + * deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf() of
> + * dma_buf_ops.
> + * @attach:	[in]	attachment to unmap buffer from
> + * @sg_table:	[in]	scatterlist info of the buffer to unmap
> + * @direction:	[in]	direction of DMA transfer
> + *
> + * Unlocked variant of dma_buf_unmap_attachment().
> + */
> +void dma_buf_unmap_attachment_unlocked(struct dma_buf_attachment *attach,
> +				       struct sg_table *sg_table,
> +				       enum dma_data_direction direction)
> +{
> +	might_sleep();
> +
> +	if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
> +		return;
> +
> +	dma_resv_lock(attach->dmabuf->resv, NULL);
> +	dma_buf_unmap_attachment(attach, sg_table, direction);
> +	dma_resv_unlock(attach->dmabuf->resv);
> +}
>   EXPORT_SYMBOL_NS_GPL(dma_buf_unmap_attachment_unlocked, DMA_BUF);
>   
>   /**
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index ac1e2911b727..b1c455329023 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -885,7 +885,7 @@ static int amdgpu_ttm_backend_bind(struct ttm_device *bdev,
>   			struct sg_table *sgt;
>   
>   			attach = gtt->gobj->import_attach;
> -			sgt = dma_buf_map_attachment_unlocked(attach, DMA_BIDIRECTIONAL);
> +			sgt = dma_buf_map_attachment(attach, DMA_BIDIRECTIONAL);
>   			if (IS_ERR(sgt))
>   				return PTR_ERR(sgt);
>   
> @@ -1010,7 +1010,7 @@ static void amdgpu_ttm_backend_unbind(struct ttm_device *bdev,
>   		struct dma_buf_attachment *attach;
>   
>   		attach = gtt->gobj->import_attach;
> -		dma_buf_unmap_attachment_unlocked(attach, ttm->sg, DMA_BIDIRECTIONAL);
> +		dma_buf_unmap_attachment(attach, ttm->sg, DMA_BIDIRECTIONAL);
>   		ttm->sg = NULL;
>   	}
>   
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> index cc54a5b1d6ae..276a74bc7fd1 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> @@ -241,8 +241,8 @@ static int i915_gem_object_get_pages_dmabuf(struct drm_i915_gem_object *obj)
>   
>   	assert_object_held(obj);
>   
> -	pages = dma_buf_map_attachment_unlocked(obj->base.import_attach,
> -						DMA_BIDIRECTIONAL);
> +	pages = dma_buf_map_attachment(obj->base.import_attach,
> +				       DMA_BIDIRECTIONAL);
>   	if (IS_ERR(pages))
>   		return PTR_ERR(pages);
>   
> @@ -270,8 +270,8 @@ static int i915_gem_object_get_pages_dmabuf(struct drm_i915_gem_object *obj)
>   static void i915_gem_object_put_pages_dmabuf(struct drm_i915_gem_object *obj,
>   					     struct sg_table *pages)
>   {
> -	dma_buf_unmap_attachment_unlocked(obj->base.import_attach, pages,
> -					  DMA_BIDIRECTIONAL);
> +	dma_buf_unmap_attachment(obj->base.import_attach, pages,
> +				 DMA_BIDIRECTIONAL);
>   }
>   
>   static const struct drm_i915_gem_object_ops i915_gem_object_dmabuf_ops = {
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> index 389e9f157ca5..9fbef3aea7b1 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> @@ -331,7 +331,19 @@ static void __i915_gem_free_objects(struct drm_i915_private *i915,
>   			continue;
>   		}
>   
> +		/*
> +		 * dma_buf_unmap_attachment() requires reservation to be
> +		 * locked. The imported GEM should share reservation lock,
> +		 * so it's safe to take the lock.
> +		 */
> +		if (obj->base.import_attach)
> +			i915_gem_object_lock(obj, NULL);
> +
>   		__i915_gem_object_pages_fini(obj);
> +
> +		if (obj->base.import_attach)
> +			i915_gem_object_unlock(obj);
> +
>   		__i915_gem_free_object(obj);
>   
>   		/* But keep the pointer alive for RCU-protected lookups */
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index da2057569101..d48d534dc55c 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -46,7 +46,7 @@ struct dma_buf_ops {
>   	/**
>   	 * @attach:
>   	 *
> -	 * This is called from dma_buf_attach() to make sure that a given
> +	 * This is called from dma_buf_attach_unlocked() to make sure that a given
>   	 * &dma_buf_attachment.dev can access the provided &dma_buf. Exporters
>   	 * which support buffer objects in special locations like VRAM or
>   	 * device-specific carveout areas should check whether the buffer could
> @@ -74,7 +74,7 @@ struct dma_buf_ops {
>   	/**
>   	 * @detach:
>   	 *
> -	 * This is called by dma_buf_detach() to release a &dma_buf_attachment.
> +	 * This is called by dma_buf_detach_unlocked() to release a &dma_buf_attachment.
>   	 * Provided so that exporters can clean up any housekeeping for an
>   	 * &dma_buf_attachment.
>   	 *
> @@ -94,7 +94,7 @@ struct dma_buf_ops {
>   	 * exclusive with @cache_sgt_mapping.
>   	 *
>   	 * This is called automatically for non-dynamic importers from
> -	 * dma_buf_attach().
> +	 * dma_buf_attach_unlocked().
>   	 *
>   	 * Note that similar to non-dynamic exporters in their @map_dma_buf
>   	 * callback the driver must guarantee that the memory is available for
> @@ -509,10 +509,10 @@ struct dma_buf_attach_ops {
>    * and its user device(s). The list contains one attachment struct per device
>    * attached to the buffer.
>    *
> - * An attachment is created by calling dma_buf_attach(), and released again by
> - * calling dma_buf_detach(). The DMA mapping itself needed to initiate a
> - * transfer is created by dma_buf_map_attachment() and freed again by calling
> - * dma_buf_unmap_attachment().
> + * An attachment is created by calling dma_buf_attach_unlocked(), and released
> + * again by calling dma_buf_detach_unlocked(). The DMA mapping itself needed to
> + * initiate a transfer is created by dma_buf_map_attachment() and freed
> + * again by calling dma_buf_unmap_attachment().
>    */
>   struct dma_buf_attachment {
>   	struct dma_buf *dmabuf;
> @@ -626,6 +626,12 @@ void dma_buf_unmap_attachment_unlocked(struct dma_buf_attachment *,
>   				       struct sg_table *,
>   				       enum dma_data_direction);
>   
> +struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
> +					enum dma_data_direction);
> +void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
> +			      struct sg_table *sg_table,
> +			      enum dma_data_direction direction);
> +
>   void dma_buf_move_notify(struct dma_buf *dma_buf);
>   int dma_buf_begin_cpu_access(struct dma_buf *dma_buf,
>   			     enum dma_data_direction dir);

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Re: [PATCH v3 9/9] dma-buf: Remove internal lock

[Christian König via Virtualization]

Am 24.08.22 um 12:22 schrieb Dmitry Osipenko:
> The internal dma-buf lock isn't needed anymore because the updated
> locking specification claims that dma-buf reservation must be locked
> by importers, and thus, the internal data is already protected by the
> reservation lock. Remove the obsoleted internal lock.
>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

Reviewed-by: Christian König <christian.koenig@amd.com>

> ---
>   drivers/dma-buf/dma-buf.c | 14 ++++----------
>   include/linux/dma-buf.h   |  9 ---------
>   2 files changed, 4 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 696d132b02f4..a0406254f0ae 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -656,7 +656,6 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
>   
>   	dmabuf->file = file;
>   
> -	mutex_init(&dmabuf->lock);
>   	INIT_LIST_HEAD(&dmabuf->attachments);
>   
>   	mutex_lock(&db_list.lock);
> @@ -1503,7 +1502,7 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_mmap_unlocked, DMA_BUF);
>   int dma_buf_vmap(struct dma_buf *dmabuf, struct iosys_map *map)
>   {
>   	struct iosys_map ptr;
> -	int ret = 0;
> +	int ret;
>   
>   	iosys_map_clear(map);
>   
> @@ -1515,28 +1514,25 @@ int dma_buf_vmap(struct dma_buf *dmabuf, struct iosys_map *map)
>   	if (!dmabuf->ops->vmap)
>   		return -EINVAL;
>   
> -	mutex_lock(&dmabuf->lock);
>   	if (dmabuf->vmapping_counter) {
>   		dmabuf->vmapping_counter++;
>   		BUG_ON(iosys_map_is_null(&dmabuf->vmap_ptr));
>   		*map = dmabuf->vmap_ptr;
> -		goto out_unlock;
> +		return 0;
>   	}
>   
>   	BUG_ON(iosys_map_is_set(&dmabuf->vmap_ptr));
>   
>   	ret = dmabuf->ops->vmap(dmabuf, &ptr);
>   	if (WARN_ON_ONCE(ret))
> -		goto out_unlock;
> +		return ret;
>   
>   	dmabuf->vmap_ptr = ptr;
>   	dmabuf->vmapping_counter = 1;
>   
>   	*map = dmabuf->vmap_ptr;
>   
> -out_unlock:
> -	mutex_unlock(&dmabuf->lock);
> -	return ret;
> +	return 0;
>   }
>   EXPORT_SYMBOL_NS_GPL(dma_buf_vmap, DMA_BUF);
>   
> @@ -1578,13 +1574,11 @@ void dma_buf_vunmap(struct dma_buf *dmabuf, struct iosys_map *map)
>   	BUG_ON(dmabuf->vmapping_counter == 0);
>   	BUG_ON(!iosys_map_is_equal(&dmabuf->vmap_ptr, map));
>   
> -	mutex_lock(&dmabuf->lock);
>   	if (--dmabuf->vmapping_counter == 0) {
>   		if (dmabuf->ops->vunmap)
>   			dmabuf->ops->vunmap(dmabuf, map);
>   		iosys_map_clear(&dmabuf->vmap_ptr);
>   	}
> -	mutex_unlock(&dmabuf->lock);
>   }
>   EXPORT_SYMBOL_NS_GPL(dma_buf_vunmap, DMA_BUF);
>   
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index d48d534dc55c..aed6695bbb50 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -326,15 +326,6 @@ struct dma_buf {
>   	/** @ops: dma_buf_ops associated with this buffer object. */
>   	const struct dma_buf_ops *ops;
>   
> -	/**
> -	 * @lock:
> -	 *
> -	 * Used internally to serialize list manipulation, attach/detach and
> -	 * vmap/unmap. Note that in many cases this is superseeded by
> -	 * dma_resv_lock() on @resv.
> -	 */
> -	struct mutex lock;
> -
>   	/**
>   	 * @vmapping_counter:
>   	 *

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Re: [PATCH v3 9/9] dma-buf: Remove internal lock

[Christian König via Virtualization]

Am 24.08.22 um 12:22 schrieb Dmitry Osipenko:
> The internal dma-buf lock isn't needed anymore because the updated
> locking specification claims that dma-buf reservation must be locked
> by importers, and thus, the internal data is already protected by the
> reservation lock. Remove the obsoleted internal lock.
>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

Reviewed-by: Christian König <christian.koenig@amd.com>

> ---
>   drivers/dma-buf/dma-buf.c | 14 ++++----------
>   include/linux/dma-buf.h   |  9 ---------
>   2 files changed, 4 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 696d132b02f4..a0406254f0ae 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -656,7 +656,6 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
>   
>   	dmabuf->file = file;
>   
> -	mutex_init(&dmabuf->lock);
>   	INIT_LIST_HEAD(&dmabuf->attachments);
>   
>   	mutex_lock(&db_list.lock);
> @@ -1503,7 +1502,7 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_mmap_unlocked, DMA_BUF);
>   int dma_buf_vmap(struct dma_buf *dmabuf, struct iosys_map *map)
>   {
>   	struct iosys_map ptr;
> -	int ret = 0;
> +	int ret;
>   
>   	iosys_map_clear(map);
>   
> @@ -1515,28 +1514,25 @@ int dma_buf_vmap(struct dma_buf *dmabuf, struct iosys_map *map)
>   	if (!dmabuf->ops->vmap)
>   		return -EINVAL;
>   
> -	mutex_lock(&dmabuf->lock);
>   	if (dmabuf->vmapping_counter) {
>   		dmabuf->vmapping_counter++;
>   		BUG_ON(iosys_map_is_null(&dmabuf->vmap_ptr));
>   		*map = dmabuf->vmap_ptr;
> -		goto out_unlock;
> +		return 0;
>   	}
>   
>   	BUG_ON(iosys_map_is_set(&dmabuf->vmap_ptr));
>   
>   	ret = dmabuf->ops->vmap(dmabuf, &ptr);
>   	if (WARN_ON_ONCE(ret))
> -		goto out_unlock;
> +		return ret;
>   
>   	dmabuf->vmap_ptr = ptr;
>   	dmabuf->vmapping_counter = 1;
>   
>   	*map = dmabuf->vmap_ptr;
>   
> -out_unlock:
> -	mutex_unlock(&dmabuf->lock);
> -	return ret;
> +	return 0;
>   }
>   EXPORT_SYMBOL_NS_GPL(dma_buf_vmap, DMA_BUF);
>   
> @@ -1578,13 +1574,11 @@ void dma_buf_vunmap(struct dma_buf *dmabuf, struct iosys_map *map)
>   	BUG_ON(dmabuf->vmapping_counter == 0);
>   	BUG_ON(!iosys_map_is_equal(&dmabuf->vmap_ptr, map));
>   
> -	mutex_lock(&dmabuf->lock);
>   	if (--dmabuf->vmapping_counter == 0) {
>   		if (dmabuf->ops->vunmap)
>   			dmabuf->ops->vunmap(dmabuf, map);
>   		iosys_map_clear(&dmabuf->vmap_ptr);
>   	}
> -	mutex_unlock(&dmabuf->lock);
>   }
>   EXPORT_SYMBOL_NS_GPL(dma_buf_vunmap, DMA_BUF);
>   
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index d48d534dc55c..aed6695bbb50 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -326,15 +326,6 @@ struct dma_buf {
>   	/** @ops: dma_buf_ops associated with this buffer object. */
>   	const struct dma_buf_ops *ops;
>   
> -	/**
> -	 * @lock:
> -	 *
> -	 * Used internally to serialize list manipulation, attach/detach and
> -	 * vmap/unmap. Note that in many cases this is superseeded by
> -	 * dma_resv_lock() on @resv.
> -	 */
> -	struct mutex lock;
> -
>   	/**
>   	 * @vmapping_counter:
>   	 *

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Re: [PATCH v3 9/9] dma-buf: Remove internal lock

[Christian König]

Am 24.08.22 um 12:22 schrieb Dmitry Osipenko:
> The internal dma-buf lock isn't needed anymore because the updated
> locking specification claims that dma-buf reservation must be locked
> by importers, and thus, the internal data is already protected by the
> reservation lock. Remove the obsoleted internal lock.
>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

Reviewed-by: Christian König <christian.koenig@amd.com>

> ---
>   drivers/dma-buf/dma-buf.c | 14 ++++----------
>   include/linux/dma-buf.h   |  9 ---------
>   2 files changed, 4 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 696d132b02f4..a0406254f0ae 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -656,7 +656,6 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
>   
>   	dmabuf->file = file;
>   
> -	mutex_init(&dmabuf->lock);
>   	INIT_LIST_HEAD(&dmabuf->attachments);
>   
>   	mutex_lock(&db_list.lock);
> @@ -1503,7 +1502,7 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_mmap_unlocked, DMA_BUF);
>   int dma_buf_vmap(struct dma_buf *dmabuf, struct iosys_map *map)
>   {
>   	struct iosys_map ptr;
> -	int ret = 0;
> +	int ret;
>   
>   	iosys_map_clear(map);
>   
> @@ -1515,28 +1514,25 @@ int dma_buf_vmap(struct dma_buf *dmabuf, struct iosys_map *map)
>   	if (!dmabuf->ops->vmap)
>   		return -EINVAL;
>   
> -	mutex_lock(&dmabuf->lock);
>   	if (dmabuf->vmapping_counter) {
>   		dmabuf->vmapping_counter++;
>   		BUG_ON(iosys_map_is_null(&dmabuf->vmap_ptr));
>   		*map = dmabuf->vmap_ptr;
> -		goto out_unlock;
> +		return 0;
>   	}
>   
>   	BUG_ON(iosys_map_is_set(&dmabuf->vmap_ptr));
>   
>   	ret = dmabuf->ops->vmap(dmabuf, &ptr);
>   	if (WARN_ON_ONCE(ret))
> -		goto out_unlock;
> +		return ret;
>   
>   	dmabuf->vmap_ptr = ptr;
>   	dmabuf->vmapping_counter = 1;
>   
>   	*map = dmabuf->vmap_ptr;
>   
> -out_unlock:
> -	mutex_unlock(&dmabuf->lock);
> -	return ret;
> +	return 0;
>   }
>   EXPORT_SYMBOL_NS_GPL(dma_buf_vmap, DMA_BUF);
>   
> @@ -1578,13 +1574,11 @@ void dma_buf_vunmap(struct dma_buf *dmabuf, struct iosys_map *map)
>   	BUG_ON(dmabuf->vmapping_counter == 0);
>   	BUG_ON(!iosys_map_is_equal(&dmabuf->vmap_ptr, map));
>   
> -	mutex_lock(&dmabuf->lock);
>   	if (--dmabuf->vmapping_counter == 0) {
>   		if (dmabuf->ops->vunmap)
>   			dmabuf->ops->vunmap(dmabuf, map);
>   		iosys_map_clear(&dmabuf->vmap_ptr);
>   	}
> -	mutex_unlock(&dmabuf->lock);
>   }
>   EXPORT_SYMBOL_NS_GPL(dma_buf_vunmap, DMA_BUF);
>   
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index d48d534dc55c..aed6695bbb50 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -326,15 +326,6 @@ struct dma_buf {
>   	/** @ops: dma_buf_ops associated with this buffer object. */
>   	const struct dma_buf_ops *ops;
>   
> -	/**
> -	 * @lock:
> -	 *
> -	 * Used internally to serialize list manipulation, attach/detach and
> -	 * vmap/unmap. Note that in many cases this is superseeded by
> -	 * dma_resv_lock() on @resv.
> -	 */
> -	struct mutex lock;
> -
>   	/**
>   	 * @vmapping_counter:
>   	 *

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Re: [PATCH v3 0/9] Move all drivers to a common dma-buf locking convention

[Christian König]

Reviewed-by: Christian König <christian.koenig@amd.com> to patches #2-#4

Am 24.08.22 um 12:22 schrieb Dmitry Osipenko:
> Hello,
>
> This series moves all drivers to a dynamic dma-buf locking specification.
>  From now on all dma-buf importers are made responsible for holding
> dma-buf's reservation lock around all operations performed over dma-bufs
> in accordance to the locking specification. This allows us to utilize
> reservation lock more broadly around kernel without fearing of a potential
> deadlocks.
>
> This patchset passes all i915 selftests. It was also tested using VirtIO,
> Panfrost, Lima, Tegra, udmabuf, AMDGPU and Nouveau drivers. I tested cases
> of display+GPU, display+V4L and GPU+V4L dma-buf sharing (where appropriate),
> which covers majority of kernel drivers since rest of the drivers share
> same or similar code paths.
>
> Changelog:
>
> v3: - Factored out dma_buf_mmap_unlocked() and attachment functions
>        into aseparate patches, like was suggested by Christian König.
>
>      - Corrected and factored out dma-buf locking documentation into
>        a separate patch, like was suggested by Christian König.
>
>      - Intel driver dropped the reservation locking fews days ago from
>        its BO-release code path, but we need that locking for the imported
>        GEMs because in the end that code path unmaps the imported GEM.
>        So I added back the locking needed by the imported GEMs, updating
>        the "dma-buf attachment locking specification" patch appropriately.
>
>      - Tested Nouveau+Intel dma-buf import/export combo.
>
>      - Tested udmabuf import to i915/Nouveau/AMDGPU.
>
>      - Fixed few places in Etnaviv, Panfrost and Lima drivers that I missed
>        to switch to locked dma-buf vmapping in the drm/gem: Take reservation
>        lock for vmap/vunmap operations" patch. In a result invalidated the
>        Christian's r-b that he gave to v2.
>
>      - Added locked dma-buf vmap/vunmap functions that are needed for fixing
>        vmappping of Etnaviv, Panfrost and Lima drivers mentioned above.
>        I actually had this change stashed for the drm-shmem shrinker patchset,
>        but then realized that it's already needed by the dma-buf patches.
>        Also improved my tests to better cover these code paths.
>
> v2: - Changed locking specification to avoid problems with a cross-driver
>        ww locking, like was suggested by Christian König. Now the attach/detach
>        callbacks are invoked without the held lock and exporter should take the
>        lock.
>
>      - Added "locking convention" documentation that explains which dma-buf
>        functions and callbacks are locked/unlocked for importers and exporters,
>        which was requested by Christian König.
>
>      - Added ack from Tomasz Figa to the V4L patches that he gave to v1.
>
> Dmitry Osipenko (9):
>    dma-buf: Add _unlocked postfix to function names
>    dma-buf: Add locked variant of dma_buf_vmap/vunmap()
>    drm/gem: Take reservation lock for vmap/vunmap operations
>    dma-buf: Move dma_buf_vmap/vunmap_unlocked() to dynamic locking
>      specification
>    dma-buf: Move dma_buf_mmap_unlocked() to dynamic locking specification
>    dma-buf: Move dma-buf attachment to dynamic locking specification
>    dma-buf: Document dynamic locking convention
>    media: videobuf2: Stop using internal dma-buf lock
>    dma-buf: Remove internal lock
>
>   Documentation/driver-api/dma-buf.rst          |   6 +
>   drivers/dma-buf/dma-buf.c                     | 276 ++++++++++++++----
>   drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c   |   4 +-
>   drivers/gpu/drm/armada/armada_gem.c           |  14 +-
>   drivers/gpu/drm/drm_client.c                  |   4 +-
>   drivers/gpu/drm/drm_gem.c                     |  24 ++
>   drivers/gpu/drm/drm_gem_dma_helper.c          |   6 +-
>   drivers/gpu/drm/drm_gem_framebuffer_helper.c  |   6 +-
>   drivers/gpu/drm/drm_gem_shmem_helper.c        |   2 +-
>   drivers/gpu/drm/drm_gem_ttm_helper.c          |   9 +-
>   drivers/gpu/drm/drm_prime.c                   |  12 +-
>   drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c   |   4 +-
>   drivers/gpu/drm/exynos/exynos_drm_gem.c       |   2 +-
>   drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c    |   6 +-
>   drivers/gpu/drm/i915/gem/i915_gem_object.c    |  12 +
>   .../drm/i915/gem/selftests/i915_gem_dmabuf.c  |  20 +-
>   drivers/gpu/drm/lima/lima_sched.c             |   4 +-
>   drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c     |   8 +-
>   drivers/gpu/drm/panfrost/panfrost_dump.c      |   4 +-
>   drivers/gpu/drm/panfrost/panfrost_perfcnt.c   |   6 +-
>   drivers/gpu/drm/qxl/qxl_object.c              |  17 +-
>   drivers/gpu/drm/qxl/qxl_prime.c               |   4 +-
>   drivers/gpu/drm/tegra/gem.c                   |  27 +-
>   drivers/infiniband/core/umem_dmabuf.c         |  11 +-
>   .../common/videobuf2/videobuf2-dma-contig.c   |  26 +-
>   .../media/common/videobuf2/videobuf2-dma-sg.c |  23 +-
>   .../common/videobuf2/videobuf2-vmalloc.c      |  17 +-
>   .../platform/nvidia/tegra-vde/dmabuf-cache.c  |  12 +-
>   drivers/misc/fastrpc.c                        |  12 +-
>   drivers/xen/gntdev-dmabuf.c                   |  14 +-
>   include/drm/drm_gem.h                         |   3 +
>   include/linux/dma-buf.h                       |  57 ++--
>   32 files changed, 410 insertions(+), 242 deletions(-)
>

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Re: [PATCH v3 6/9] dma-buf: Move dma-buf attachment to dynamic locking specification

[Christian König via Virtualization]

Am 24.08.22 um 17:03 schrieb Dmitry Osipenko:
> On 8/24/22 17:08, Christian König wrote:
>> Am 24.08.22 um 12:22 schrieb Dmitry Osipenko:
>>> Move dma-buf attachment API functions to the dynamic locking
>>> specification.
>>> The strict locking convention prevents deadlock situations for dma-buf
>>> importers and exporters.
>>>
>>> Previously, the "unlocked" versions of the attachment API functions
>>> weren't taking the reservation lock and this patch makes them to take
>>> the lock.
>> Didn't we concluded that we need to keep the attach and detach callbacks
>> without the lock and only move the map/unmap callbacks over?
>>
>> Otherwise it won't be possible for drivers to lock multiple buffers if
>> they have to shuffle things around for a specific attachment.
> We did conclude that. The attach/detach dma-buf ops are unlocked, but
> the map_dma_buf/unmap_dma_buf must be invoked under lock and
> dma_buf_dynamic_attach_unlocked() maps dma-buf if either importer or
> exporter can't handle the dynamic mapping [1].

Ah! You are confusing me over and over again with that :)

Ok in this case that here is fine, I just need to re-read the patch.

Thanks,
Christian.

>
> [1]
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Felixir.bootlin.com%2Flinux%2Fv6.0-rc2%2Fsource%2Fdrivers%2Fdma-buf%2Fdma-buf.c%23L869&data=05%7C01%7Cchristian.koenig%40amd.com%7Cdf23d89db8b84bf6d4c008da85e1dc6c%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637969502441026991%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=d8kWKjDCFn%2B3KmK135Gcv6%2FMLffEYcipouqWxfc%2BKXM%3D&reserved=0
>
> Hence I re-arranged the dma_resv_lock() in
> dma_buf_dynamic_attach_unlocked() to move both pinning and mapping under
> the held lock.
>

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Re: [Linaro-mm-sig] [PATCH v3 6/9] dma-buf: Move dma-buf attachment to dynamic locking specification

[Christian König]

Am 24.08.22 um 12:22 schrieb Dmitry Osipenko:
> Move dma-buf attachment API functions to the dynamic locking specification.
> The strict locking convention prevents deadlock situations for dma-buf
> importers and exporters.
>
> Previously, the "unlocked" versions of the attachment API functions
> weren't taking the reservation lock and this patch makes them to take
> the lock.
>
> Intel and AMD GPU drivers already were mapping the attached dma-bufs under
> the held lock during attachment, hence these drivers are updated to use
> the locked functions.
>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> ---
>   drivers/dma-buf/dma-buf.c                  | 115 ++++++++++++++-------
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c    |   4 +-
>   drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c |   8 +-
>   drivers/gpu/drm/i915/gem/i915_gem_object.c |  12 +++
>   include/linux/dma-buf.h                    |  20 ++--
>   5 files changed, 110 insertions(+), 49 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 4556a12bd741..f2a5a122da4a 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -559,7 +559,7 @@ static struct file *dma_buf_getfile(struct dma_buf *dmabuf, int flags)
>    * 2. Userspace passes this file-descriptors to all drivers it wants this buffer
>    *    to share with: First the file descriptor is converted to a &dma_buf using
>    *    dma_buf_get(). Then the buffer is attached to the device using
> - *    dma_buf_attach().
> + *    dma_buf_attach_unlocked().

Now I get why this is confusing me so much.

The _unlocked postfix implies that there is another function which 
should be called with the locks already held, but this is not the case 
for attach/detach (because they always need to grab the lock themselves).

So I suggest to drop the _unlocked postfix for the attach/detach 
functions. Another step would then be to unify attach/detach with 
dynamic_attach/dynamic_detach when both have the same locking convention 
anyway.

Sorry that this is going so much back and forth, it's really complicated 
to keep all the stuff in my head at the moment :)

Thanks a lot for looking into this,
Christian.

>    *
>    *    Up to this stage the exporter is still free to migrate or reallocate the
>    *    backing storage.
> @@ -569,8 +569,8 @@ static struct file *dma_buf_getfile(struct dma_buf *dmabuf, int flags)
>    *    dma_buf_map_attachment() and dma_buf_unmap_attachment().
>    *
>    * 4. Once a driver is done with a shared buffer it needs to call
> - *    dma_buf_detach() (after cleaning up any mappings) and then release the
> - *    reference acquired with dma_buf_get() by calling dma_buf_put().
> + *    dma_buf_detach_unlocked() (after cleaning up any mappings) and then
> + *    release the reference acquired with dma_buf_get() by calling dma_buf_put().
>    *
>    * For the detailed semantics exporters are expected to implement see
>    * &dma_buf_ops.
> @@ -802,7 +802,7 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
>    * @importer_priv:	[in]	importer private pointer for the attachment
>    *
>    * Returns struct dma_buf_attachment pointer for this attachment. Attachments
> - * must be cleaned up by calling dma_buf_detach().
> + * must be cleaned up by calling dma_buf_detach_unlocked().
>    *
>    * Optionally this calls &dma_buf_ops.attach to allow device-specific attach
>    * functionality.
> @@ -858,8 +858,8 @@ dma_buf_dynamic_attach_unlocked(struct dma_buf *dmabuf, struct device *dev,
>   	    dma_buf_is_dynamic(dmabuf)) {
>   		struct sg_table *sgt;
>   
> +		dma_resv_lock(attach->dmabuf->resv, NULL);
>   		if (dma_buf_is_dynamic(attach->dmabuf)) {
> -			dma_resv_lock(attach->dmabuf->resv, NULL);
>   			ret = dmabuf->ops->pin(attach);
>   			if (ret)
>   				goto err_unlock;
> @@ -872,8 +872,7 @@ dma_buf_dynamic_attach_unlocked(struct dma_buf *dmabuf, struct device *dev,
>   			ret = PTR_ERR(sgt);
>   			goto err_unpin;
>   		}
> -		if (dma_buf_is_dynamic(attach->dmabuf))
> -			dma_resv_unlock(attach->dmabuf->resv);
> +		dma_resv_unlock(attach->dmabuf->resv);
>   		attach->sgt = sgt;
>   		attach->dir = DMA_BIDIRECTIONAL;
>   	}
> @@ -889,8 +888,7 @@ dma_buf_dynamic_attach_unlocked(struct dma_buf *dmabuf, struct device *dev,
>   		dmabuf->ops->unpin(attach);
>   
>   err_unlock:
> -	if (dma_buf_is_dynamic(attach->dmabuf))
> -		dma_resv_unlock(attach->dmabuf->resv);
> +	dma_resv_unlock(attach->dmabuf->resv);
>   
>   	dma_buf_detach_unlocked(dmabuf, attach);
>   	return ERR_PTR(ret);
> @@ -927,7 +925,7 @@ static void __unmap_dma_buf(struct dma_buf_attachment *attach,
>    * @dmabuf:	[in]	buffer to detach from.
>    * @attach:	[in]	attachment to be detached; is free'd after this call.
>    *
> - * Clean up a device attachment obtained by calling dma_buf_attach().
> + * Clean up a device attachment obtained by calling dma_buf_attach_unlocked().
>    *
>    * Optionally this calls &dma_buf_ops.detach for device-specific detach.
>    */
> @@ -937,21 +935,19 @@ void dma_buf_detach_unlocked(struct dma_buf *dmabuf,
>   	if (WARN_ON(!dmabuf || !attach))
>   		return;
>   
> +	dma_resv_lock(attach->dmabuf->resv, NULL);
> +
>   	if (attach->sgt) {
> -		if (dma_buf_is_dynamic(attach->dmabuf))
> -			dma_resv_lock(attach->dmabuf->resv, NULL);
>   
>   		__unmap_dma_buf(attach, attach->sgt, attach->dir);
>   
> -		if (dma_buf_is_dynamic(attach->dmabuf)) {
> +		if (dma_buf_is_dynamic(attach->dmabuf))
>   			dmabuf->ops->unpin(attach);
> -			dma_resv_unlock(attach->dmabuf->resv);
> -		}
>   	}
> -
> -	dma_resv_lock(dmabuf->resv, NULL);
>   	list_del(&attach->node);
> +
>   	dma_resv_unlock(dmabuf->resv);
> +
>   	if (dmabuf->ops->detach)
>   		dmabuf->ops->detach(dmabuf, attach);
>   
> @@ -1011,7 +1007,7 @@ void dma_buf_unpin(struct dma_buf_attachment *attach)
>   EXPORT_SYMBOL_NS_GPL(dma_buf_unpin, DMA_BUF);
>   
>   /**
> - * dma_buf_map_attachment_unlocked - Returns the scatterlist table of the attachment;
> + * dma_buf_map_attachment - Returns the scatterlist table of the attachment;
>    * mapped into _device_ address space. Is a wrapper for map_dma_buf() of the
>    * dma_buf_ops.
>    * @attach:	[in]	attachment whose scatterlist is to be returned
> @@ -1030,10 +1026,11 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_unpin, DMA_BUF);
>    *
>    * Important: Dynamic importers must wait for the exclusive fence of the struct
>    * dma_resv attached to the DMA-BUF first.
> + *
> + * Importer is responsible for holding dmabuf's reservation lock.
>    */
> -struct sg_table *
> -dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach,
> -				enum dma_data_direction direction)
> +struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
> +					enum dma_data_direction direction)
>   {
>   	struct sg_table *sg_table;
>   	int r;
> @@ -1043,8 +1040,7 @@ dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach,
>   	if (WARN_ON(!attach || !attach->dmabuf))
>   		return ERR_PTR(-EINVAL);
>   
> -	if (dma_buf_attachment_is_dynamic(attach))
> -		dma_resv_assert_held(attach->dmabuf->resv);
> +	dma_resv_assert_held(attach->dmabuf->resv);
>   
>   	if (attach->sgt) {
>   		/*
> @@ -1059,7 +1055,6 @@ dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach,
>   	}
>   
>   	if (dma_buf_is_dynamic(attach->dmabuf)) {
> -		dma_resv_assert_held(attach->dmabuf->resv);
>   		if (!IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY)) {
>   			r = attach->dmabuf->ops->pin(attach);
>   			if (r)
> @@ -1099,10 +1094,38 @@ dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach,
>   #endif /* CONFIG_DMA_API_DEBUG */
>   	return sg_table;
>   }
> +EXPORT_SYMBOL_NS_GPL(dma_buf_map_attachment, DMA_BUF);
> +
> +/**
> + * dma_buf_map_attachment_unlocked - Returns the scatterlist table of the attachment;
> + * mapped into _device_ address space. Is a wrapper for map_dma_buf() of the
> + * dma_buf_ops.
> + * @attach:	[in]	attachment whose scatterlist is to be returned
> + * @direction:	[in]	direction of DMA transfer
> + *
> + * Unlocked variant of dma_buf_map_attachment().
> + */
> +struct sg_table *
> +dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach,
> +				enum dma_data_direction direction)
> +{
> +	struct sg_table *sg_table;
> +
> +	might_sleep();
> +
> +	if (WARN_ON(!attach || !attach->dmabuf))
> +		return ERR_PTR(-EINVAL);
> +
> +	dma_resv_lock(attach->dmabuf->resv, NULL);
> +	sg_table = dma_buf_map_attachment(attach, direction);
> +	dma_resv_unlock(attach->dmabuf->resv);
> +
> +	return sg_table;
> +}
>   EXPORT_SYMBOL_NS_GPL(dma_buf_map_attachment_unlocked, DMA_BUF);
>   
>   /**
> - * dma_buf_unmap_attachment_unlocked - unmaps and decreases usecount of the buffer;might
> + * dma_buf_unmap_attachment - unmaps and decreases usecount of the buffer;might
>    * deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf() of
>    * dma_buf_ops.
>    * @attach:	[in]	attachment to unmap buffer from
> @@ -1110,31 +1133,51 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_map_attachment_unlocked, DMA_BUF);
>    * @direction:  [in]    direction of DMA transfer
>    *
>    * This unmaps a DMA mapping for @attached obtained by dma_buf_map_attachment().
> + *
> + * Importer is responsible for holding dmabuf's reservation lock.
>    */
> -void dma_buf_unmap_attachment_unlocked(struct dma_buf_attachment *attach,
> -				       struct sg_table *sg_table,
> -				       enum dma_data_direction direction)
> +void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
> +			      struct sg_table *sg_table,
> +			      enum dma_data_direction direction)
>   {
>   	might_sleep();
>   
> -	if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
> -		return;
> -
> -	if (dma_buf_attachment_is_dynamic(attach))
> -		dma_resv_assert_held(attach->dmabuf->resv);
> +	dma_resv_assert_held(attach->dmabuf->resv);
>   
>   	if (attach->sgt == sg_table)
>   		return;
>   
> -	if (dma_buf_is_dynamic(attach->dmabuf))
> -		dma_resv_assert_held(attach->dmabuf->resv);
> -
>   	__unmap_dma_buf(attach, sg_table, direction);
>   
>   	if (dma_buf_is_dynamic(attach->dmabuf) &&
>   	    !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))
>   		dma_buf_unpin(attach);
>   }
> +EXPORT_SYMBOL_NS_GPL(dma_buf_unmap_attachment, DMA_BUF);
> +
> +/**
> + * dma_buf_unmap_attachment_unlocked - unmaps and decreases usecount of the buffer;might
> + * deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf() of
> + * dma_buf_ops.
> + * @attach:	[in]	attachment to unmap buffer from
> + * @sg_table:	[in]	scatterlist info of the buffer to unmap
> + * @direction:	[in]	direction of DMA transfer
> + *
> + * Unlocked variant of dma_buf_unmap_attachment().
> + */
> +void dma_buf_unmap_attachment_unlocked(struct dma_buf_attachment *attach,
> +				       struct sg_table *sg_table,
> +				       enum dma_data_direction direction)
> +{
> +	might_sleep();
> +
> +	if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
> +		return;
> +
> +	dma_resv_lock(attach->dmabuf->resv, NULL);
> +	dma_buf_unmap_attachment(attach, sg_table, direction);
> +	dma_resv_unlock(attach->dmabuf->resv);
> +}
>   EXPORT_SYMBOL_NS_GPL(dma_buf_unmap_attachment_unlocked, DMA_BUF);
>   
>   /**
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index ac1e2911b727..b1c455329023 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -885,7 +885,7 @@ static int amdgpu_ttm_backend_bind(struct ttm_device *bdev,
>   			struct sg_table *sgt;
>   
>   			attach = gtt->gobj->import_attach;
> -			sgt = dma_buf_map_attachment_unlocked(attach, DMA_BIDIRECTIONAL);
> +			sgt = dma_buf_map_attachment(attach, DMA_BIDIRECTIONAL);
>   			if (IS_ERR(sgt))
>   				return PTR_ERR(sgt);
>   
> @@ -1010,7 +1010,7 @@ static void amdgpu_ttm_backend_unbind(struct ttm_device *bdev,
>   		struct dma_buf_attachment *attach;
>   
>   		attach = gtt->gobj->import_attach;
> -		dma_buf_unmap_attachment_unlocked(attach, ttm->sg, DMA_BIDIRECTIONAL);
> +		dma_buf_unmap_attachment(attach, ttm->sg, DMA_BIDIRECTIONAL);
>   		ttm->sg = NULL;
>   	}
>   
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> index cc54a5b1d6ae..276a74bc7fd1 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> @@ -241,8 +241,8 @@ static int i915_gem_object_get_pages_dmabuf(struct drm_i915_gem_object *obj)
>   
>   	assert_object_held(obj);
>   
> -	pages = dma_buf_map_attachment_unlocked(obj->base.import_attach,
> -						DMA_BIDIRECTIONAL);
> +	pages = dma_buf_map_attachment(obj->base.import_attach,
> +				       DMA_BIDIRECTIONAL);
>   	if (IS_ERR(pages))
>   		return PTR_ERR(pages);
>   
> @@ -270,8 +270,8 @@ static int i915_gem_object_get_pages_dmabuf(struct drm_i915_gem_object *obj)
>   static void i915_gem_object_put_pages_dmabuf(struct drm_i915_gem_object *obj,
>   					     struct sg_table *pages)
>   {
> -	dma_buf_unmap_attachment_unlocked(obj->base.import_attach, pages,
> -					  DMA_BIDIRECTIONAL);
> +	dma_buf_unmap_attachment(obj->base.import_attach, pages,
> +				 DMA_BIDIRECTIONAL);
>   }
>   
>   static const struct drm_i915_gem_object_ops i915_gem_object_dmabuf_ops = {
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> index 389e9f157ca5..9fbef3aea7b1 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> @@ -331,7 +331,19 @@ static void __i915_gem_free_objects(struct drm_i915_private *i915,
>   			continue;
>   		}
>   
> +		/*
> +		 * dma_buf_unmap_attachment() requires reservation to be
> +		 * locked. The imported GEM should share reservation lock,
> +		 * so it's safe to take the lock.
> +		 */
> +		if (obj->base.import_attach)
> +			i915_gem_object_lock(obj, NULL);
> +
>   		__i915_gem_object_pages_fini(obj);
> +
> +		if (obj->base.import_attach)
> +			i915_gem_object_unlock(obj);
> +
>   		__i915_gem_free_object(obj);
>   
>   		/* But keep the pointer alive for RCU-protected lookups */
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index da2057569101..d48d534dc55c 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -46,7 +46,7 @@ struct dma_buf_ops {
>   	/**
>   	 * @attach:
>   	 *
> -	 * This is called from dma_buf_attach() to make sure that a given
> +	 * This is called from dma_buf_attach_unlocked() to make sure that a given
>   	 * &dma_buf_attachment.dev can access the provided &dma_buf. Exporters
>   	 * which support buffer objects in special locations like VRAM or
>   	 * device-specific carveout areas should check whether the buffer could
> @@ -74,7 +74,7 @@ struct dma_buf_ops {
>   	/**
>   	 * @detach:
>   	 *
> -	 * This is called by dma_buf_detach() to release a &dma_buf_attachment.
> +	 * This is called by dma_buf_detach_unlocked() to release a &dma_buf_attachment.
>   	 * Provided so that exporters can clean up any housekeeping for an
>   	 * &dma_buf_attachment.
>   	 *
> @@ -94,7 +94,7 @@ struct dma_buf_ops {
>   	 * exclusive with @cache_sgt_mapping.
>   	 *
>   	 * This is called automatically for non-dynamic importers from
> -	 * dma_buf_attach().
> +	 * dma_buf_attach_unlocked().
>   	 *
>   	 * Note that similar to non-dynamic exporters in their @map_dma_buf
>   	 * callback the driver must guarantee that the memory is available for
> @@ -509,10 +509,10 @@ struct dma_buf_attach_ops {
>    * and its user device(s). The list contains one attachment struct per device
>    * attached to the buffer.
>    *
> - * An attachment is created by calling dma_buf_attach(), and released again by
> - * calling dma_buf_detach(). The DMA mapping itself needed to initiate a
> - * transfer is created by dma_buf_map_attachment() and freed again by calling
> - * dma_buf_unmap_attachment().
> + * An attachment is created by calling dma_buf_attach_unlocked(), and released
> + * again by calling dma_buf_detach_unlocked(). The DMA mapping itself needed to
> + * initiate a transfer is created by dma_buf_map_attachment() and freed
> + * again by calling dma_buf_unmap_attachment().
>    */
>   struct dma_buf_attachment {
>   	struct dma_buf *dmabuf;
> @@ -626,6 +626,12 @@ void dma_buf_unmap_attachment_unlocked(struct dma_buf_attachment *,
>   				       struct sg_table *,
>   				       enum dma_data_direction);
>   
> +struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
> +					enum dma_data_direction);
> +void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
> +			      struct sg_table *sg_table,
> +			      enum dma_data_direction direction);
> +
>   void dma_buf_move_notify(struct dma_buf *dma_buf);
>   int dma_buf_begin_cpu_access(struct dma_buf *dma_buf,
>   			     enum dma_data_direction dir);

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Re: [Linaro-mm-sig] [PATCH v3 6/9] dma-buf: Move dma-buf attachment to dynamic locking specification

[Christian König via Virtualization]

Am 24.08.22 um 17:49 schrieb Dmitry Osipenko:
> On 8/24/22 18:24, Christian König wrote:
>> Am 24.08.22 um 12:22 schrieb Dmitry Osipenko:
>>> Move dma-buf attachment API functions to the dynamic locking
>>> specification.
>>> The strict locking convention prevents deadlock situations for dma-buf
>>> importers and exporters.
>>>
>>> Previously, the "unlocked" versions of the attachment API functions
>>> weren't taking the reservation lock and this patch makes them to take
>>> the lock.
>>>
>>> Intel and AMD GPU drivers already were mapping the attached dma-bufs
>>> under
>>> the held lock during attachment, hence these drivers are updated to use
>>> the locked functions.
>>>
>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
>>> ---
>>>    drivers/dma-buf/dma-buf.c                  | 115 ++++++++++++++-------
>>>    drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c    |   4 +-
>>>    drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c |   8 +-
>>>    drivers/gpu/drm/i915/gem/i915_gem_object.c |  12 +++
>>>    include/linux/dma-buf.h                    |  20 ++--
>>>    5 files changed, 110 insertions(+), 49 deletions(-)
>>>
>>> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
>>> index 4556a12bd741..f2a5a122da4a 100644
>>> --- a/drivers/dma-buf/dma-buf.c
>>> +++ b/drivers/dma-buf/dma-buf.c
>>> @@ -559,7 +559,7 @@ static struct file *dma_buf_getfile(struct dma_buf
>>> *dmabuf, int flags)
>>>     * 2. Userspace passes this file-descriptors to all drivers it wants
>>> this buffer
>>>     *    to share with: First the file descriptor is converted to a
>>> &dma_buf using
>>>     *    dma_buf_get(). Then the buffer is attached to the device using
>>> - *    dma_buf_attach().
>>> + *    dma_buf_attach_unlocked().
>> Now I get why this is confusing me so much.
>>
>> The _unlocked postfix implies that there is another function which
>> should be called with the locks already held, but this is not the case
>> for attach/detach (because they always need to grab the lock themselves).
> That's correct. The attach/detach ops of exporter can take the lock
> (like i915 exporter does it), hence importer must not grab the lock
> around dma_buf_attach() invocation.
>
>> So I suggest to drop the _unlocked postfix for the attach/detach
>> functions. Another step would then be to unify attach/detach with
>> dynamic_attach/dynamic_detach when both have the same locking convention
>> anyway.
> It's not a problem to change the name, but it's unclear to me why we
> should do it. The _unlocked postfix tells importer that reservation must
> be unlocked and it must be unlocked in case of dma_buf_attach().
>
> Dropping the postfix will make dma_buf_attach() inconsistent with the
> rest of the _unlocked functions(?). Are you sure we need to rename it?

The idea of the postfix was to distinguish between two different 
versions of the same function, e.g. dma_buf_vmap_unlocked() vs normal 
dma_buf_vmap().

When we don't have those two types of the same function I don't think it 
makes to much sense to keep that. We should just properly document which 
functions expect what and that's what your documentation patch does.

Regards,
Christian.

>
>> Sorry that this is going so much back and forth, it's really complicated
>> to keep all the stuff in my head at the moment :)
> Not a problem at all, I expected that it will take some time for this
> patchset to settle down.
>

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