[PATCH 1/4] dma-buf: change DMA-buf locking convention

Christian König
2019-08-29T14:29:24Z

This patch is a stripped down version of the locking changes
necessary to support dynamic DMA-buf handling.

For compatibility we cache the DMA-buf mapping as soon as
exporter/importer disagree on the dynamic handling.

Signed-off-by: Christian König <christian.koenig@amd.com>
---
drivers/dma-buf/dma-buf.c | 90 ++++++++++++++++++++++++++++++++++++---
include/linux/dma-buf.h | 51 +++++++++++++++++++++-
2 files changed, 133 insertions(+), 8 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 433d91d710e4..65052d52602b 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -525,6 +525,10 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
return ERR_PTR(-EINVAL);
}

+ if (WARN_ON(exp_info->ops->cache_sgt_mapping &&
+ exp_info->ops->dynamic_mapping))
+ return ERR_PTR(-EINVAL);
+
if (!try_module_get(exp_info->owner))
return ERR_PTR(-ENOENT);

@@ -645,10 +649,11 @@ void dma_buf_put(struct dma_buf *dmabuf)
EXPORT_SYMBOL_GPL(dma_buf_put);

/**
- * dma_buf_attach - Add the device to dma_buf's attachments list; optionally,
+ * dma_buf_dynamic_attach - Add the device to dma_buf's attachments list; optionally,
* calls attach() of dma_buf_ops to allow device-specific attach functionality
- * @dmabuf: [in] buffer to attach device to.
- * @dev: [in] device to be attached.
+ * @dmabuf: [in] buffer to attach device to.
+ * @dev: [in] device to be attached.
+ * @dynamic_mapping: [in] calling convention for map/unmap
*
* Returns struct dma_buf_attachment pointer for this attachment. Attachments
* must be cleaned up by calling dma_buf_detach().
@@ -662,8 +667,9 @@ EXPORT_SYMBOL_GPL(dma_buf_put);
* accessible to @dev, and cannot be moved to a more suitable place. This is
* indicated with the error code -EBUSY.
*/
-struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
- struct device *dev)
+struct dma_buf_attachment *
+dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
+ bool dynamic_mapping)
{
struct dma_buf_attachment *attach;
int ret;
@@ -677,6 +683,7 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,

attach->dev = dev;
attach->dmabuf = dmabuf;
+ attach->dynamic_mapping = dynamic_mapping;

mutex_lock(&dmabuf->lock);

@@ -685,16 +692,64 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
if (ret)
goto err_attach;
}
+ dma_resv_lock(dmabuf->resv, NULL);
list_add(&attach->node, &dmabuf->attachments);
+ dma_resv_unlock(dmabuf->resv);

mutex_unlock(&dmabuf->lock);

+ /* When either the importer or the exporter can't handle dynamic
+ * mappings we cache the mapping here to avoid issues with the
+ * reservation object lock.
+ */
+ if (dma_buf_attachment_is_dynamic(attach) !=
+ dma_buf_is_dynamic(dmabuf)) {
+ struct sg_table *sgt;
+
+ if (dma_buf_is_dynamic(attach->dmabuf))
+ dma_resv_lock(attach->dmabuf->resv, NULL);
+
+ sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL);
+ if (!sgt)
+ sgt = ERR_PTR(-ENOMEM);
+ if (IS_ERR(sgt)) {
+ ret = PTR_ERR(sgt);
+ goto err_unlock;
+ }
+ if (dma_buf_is_dynamic(attach->dmabuf))
+ dma_resv_unlock(attach->dmabuf->resv);
+ attach->sgt = sgt;
+ attach->dir = DMA_BIDIRECTIONAL;
+ }
+
return attach;

err_attach:
kfree(attach);
mutex_unlock(&dmabuf->lock);
return ERR_PTR(ret);
+
+err_unlock:
+ if (dma_buf_is_dynamic(attach->dmabuf))
+ dma_resv_unlock(attach->dmabuf->resv);
+
+ dma_buf_detach(dmabuf, attach);
+ return ERR_PTR(ret);
+}
+EXPORT_SYMBOL_GPL(dma_buf_dynamic_attach);
+
+/**
+ * dma_buf_attach - Wrapper for dma_buf_dynamic_attach
+ * @dmabuf: [in] buffer to attach device to.
+ * @dev: [in] device to be attached.
+ *
+ * Wrapper to call dma_buf_dynamic_attach() for drivers which still use a static
+ * mapping.
+ */
+struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
+ struct device *dev)
+{
+ return dma_buf_dynamic_attach(dmabuf, dev, false);
}
EXPORT_SYMBOL_GPL(dma_buf_attach);

@@ -711,11 +766,20 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
if (WARN_ON(!dmabuf || !attach))
return;

- if (attach->sgt)
+ if (attach->sgt) {
+ if (dma_buf_is_dynamic(attach->dmabuf))
+ dma_resv_lock(attach->dmabuf->resv, NULL);
+
dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);

+ if (dma_buf_is_dynamic(attach->dmabuf))
+ dma_resv_unlock(attach->dmabuf->resv);
+ }
+
mutex_lock(&dmabuf->lock);
+ dma_resv_lock(dmabuf->resv, NULL);
list_del(&attach->node);
+ dma_resv_unlock(dmabuf->resv);
if (dmabuf->ops->detach)
dmabuf->ops->detach(dmabuf, attach);

@@ -749,6 +813,9 @@ struct sg_table *dma_buf_map_attachment(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);
+
if (attach->sgt) {
/*
* Two mappings with different directions for the same
@@ -761,6 +828,9 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
return attach->sgt;
}

+ if (dma_buf_is_dynamic(attach->dmabuf))
+ dma_resv_assert_held(attach->dmabuf->resv);
+
sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
if (!sg_table)
sg_table = ERR_PTR(-ENOMEM);
@@ -793,9 +863,15 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
return;

+ if (dma_buf_attachment_is_dynamic(attach))
+ 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);
+
attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
}
EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
@@ -1219,10 +1295,12 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
seq_puts(s, "\tAttached Devices:\n");
attach_count = 0;

+ dma_resv_lock(buf_obj->resv, NULL);
list_for_each_entry(attach_obj, &buf_obj->attachments, node) {
seq_printf(s, "\t%s\n", dev_name(attach_obj->dev));
attach_count++;
}
+ dma_resv_unlock(buf_obj->resv);

seq_printf(s, "Total %d devices attached\n\n",
attach_count);
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index ec212cb27fdc..a8f8b2b812fd 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -42,6 +42,17 @@ struct dma_buf_ops {
*/
bool cache_sgt_mapping;

+ /**
+ * @dynamic_mapping:
+ *
+ * If true the framework makes sure that the map/unmap_dma_buf
+ * callbacks are always called with the dma_resv object locked.
+ *
+ * If false the framework makes ure that the map/unmap_dma_buf
+ * callbacks are always called without the dma_resv object locked.
+ */
+ bool dynamic_mapping;
+
/**
* @attach:
*
@@ -109,6 +120,9 @@ struct dma_buf_ops {
* any other kind of sharing that the exporter might wish to make
* available to buffer-users.
*
+ * This is always called with the dmabuf->resv object locked when
+ * the dynamic_mapping flag is true.
+ *
* Returns:
*
* A &sg_table scatter list of or the backing storage of the DMA buffer,
@@ -327,6 +341,8 @@ struct dma_buf {
* @sgt: cached mapping.
* @dir: direction of cached mapping.
* @priv: exporter specific attachment data.
+ * @dynamic_mapping: true if dma_buf_map/unmap_attachment() is called with the
+ * dma_resv lock held.
*
* This structure holds the attachment information between the dma_buf buffer
* and its user device(s). The list contains one attachment struct per device
@@ -343,6 +359,7 @@ struct dma_buf_attachment {
struct list_head node;
struct sg_table *sgt;
enum dma_data_direction dir;
+ bool dynamic_mapping;
void *priv;
};

@@ -394,10 +411,39 @@ static inline void get_dma_buf(struct dma_buf *dmabuf)
get_file(dmabuf->file);
}

+/**
+ * dma_buf_is_dynamic - check if a DMA-buf uses dynamic mappings.
+ * @dmabuf: the DMA-buf to check
+ *
+ * Returns true if a DMA-buf exporter wants to be called with the dma_resv
+ * locked, false if it doesn't wants to be called with the lock held.
+ */
+static inline bool dma_buf_is_dynamic(struct dma_buf *dmabuf)
+{
+ return dmabuf->ops->dynamic_mapping;
+}
+
+/**
+ * dma_buf_attachment_is_dynamic - check if a DMA-buf attachment uses dynamic
+ * mappinsg
+ * @attach: the DMA-buf attachment to check
+ *
+ * Returns true if a DMA-buf importer wants to call the map/unmap functions with
+ * the dma_resv lock held.
+ */
+static inline bool
+dma_buf_attachment_is_dynamic(struct dma_buf_attachment *attach)
+{
+ return attach->dynamic_mapping;
+}
+
struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
- struct device *dev);
+ struct device *dev);
+struct dma_buf_attachment *
+dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
+ bool dynamic_mapping);
void dma_buf_detach(struct dma_buf *dmabuf,
- struct dma_buf_attachment *dmabuf_attach);
+ struct dma_buf_attachment *attach);

struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info);

@@ -409,6 +455,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
enum dma_data_direction);
void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
enum dma_data_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);
int dma_buf_end_cpu_access(struct dma_buf *dma_buf,
--
2.17.1