Re: [PATCH 03/12] dma-buf: lock the reservation object during (un)map_dma_buf v3

From: Christian KÃnig
Date: Wed Apr 17 2019 - 13:10:50 EST

Am 17.04.19 um 16:26 schrieb Daniel Vetter:
On Wed, Apr 17, 2019 at 04:14:32PM +0200, Christian KÃnig wrote:
Am 17.04.19 um 16:08 schrieb Daniel Vetter:
On Tue, Apr 16, 2019 at 08:38:32PM +0200, Christian KÃnig wrote:
Make it mandatory for dynamic dma-buf callbacks to be called with the
reservation lock held.

For static dma-buf exporters we still have the fallback of using cached sgt.

v2: reordered
v3: rebased on sgt caching
v4: use the cached sgt when possible

Signed-off-by: Christian KÃnig <christian.koenig@xxxxxxx>
I think there's a bit a rebase chaos going on:
- some comments left behind with no_sgt_cache, which I can't find anymore
- the function signature rework of dma_buf_attach should imo be split out
Ah, crap thought I've got all of those. Going to fix that.

Next issue is that the reservation object locking is still in the path of
dma_buf_map, so probably still going to result in tons of lockdep splats.
Except the i915+amdgpu path should now work due to the fastpath.
I actually found a solution for that :)

The idea is now that we always cache the sgt in the attachment unless the
dynamic flag (previously no_sgt_cache flag) is set. And this cached sgt is
created without holding the lock.
Yeah I think that idea works.

We either need to document that really well or maybe split the mapping
callbacks into map/unmap and map_lock/unmap_locked. Opinions?
I think the implementation doesn't. Exporter can't decide on its own
whether dynamic/static is what's needed, we need to decide that for each
attachment, taking both exporter and importer capabilities into account.

Well that's what the pin/unpin callbacks are good for :)

Essentially we have to handle the following cases:
a) dynamic exporter and dynamic importer
ÂÂÂ ÂÂÂ Nothing special here and we don't need the sgt caching nor pinning.

b) dynamic exporter and static importer
ÂÂÂ ÂÂÂ The pin/unpin callbacks are used to inform the exporter that it needs to keep the buffer in the current place.

c) static exporter and dynamic importer
ÂÂÂ ÂÂÂ We use the sgt caching to avoid calling the exporter with the common lock held.

d) static exporter and static importer
ÂÂÂ ÂÂÂ We use the sgt caching, but that is actually only optional.

I think if we do that, then it should work out. I replied on the pin/unpin
interface patch with some more concrete thoughts. Maybe best to continue
that discussion there, with more context.

Yeah, that is probably a good idea.

Regards,
Christian.


-Daniel

Not sure that's a solution that really works, just hides that
fundamentally we still have that issue of incompatible locking chains
between different drivers.
We can now make a slow transition between static and dynamic DMA-buf
handling, so only driver who can do the locking will be affected.

Christian.

-Daniel

---
drivers/dma-buf/dma-buf.c | 24 ++++++++++---------
drivers/gpu/drm/armada/armada_gem.c | 6 ++++-
drivers/gpu/drm/drm_prime.c | 6 ++++-
drivers/gpu/drm/i915/i915_gem_dmabuf.c | 6 ++++-
drivers/gpu/drm/tegra/gem.c | 6 ++++-
drivers/gpu/drm/udl/udl_dmabuf.c | 6 ++++-
.../common/videobuf2/videobuf2-dma-contig.c | 6 ++++-
.../media/common/videobuf2/videobuf2-dma-sg.c | 6 ++++-
drivers/staging/media/tegra-vde/tegra-vde.c | 6 ++++-
include/linux/dma-buf.h | 23 ++++++++++++++++--
10 files changed, 74 insertions(+), 21 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index ef480e5fb239..83c92bfd964c 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -532,8 +532,9 @@ EXPORT_SYMBOL_GPL(dma_buf_put);
/**
* dma_buf_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.
+ * @info: [in] holds all the attach related information provided
+ * by the importer. see &struct dma_buf_attach_info
+ * for further details.
*
* Returns struct dma_buf_attachment pointer for this attachment. Attachments
* must be cleaned up by calling dma_buf_detach().
@@ -547,20 +548,20 @@ 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_attach(const struct dma_buf_attach_info *info)
{
+ struct dma_buf *dmabuf = info->dmabuf;
struct dma_buf_attachment *attach;
int ret;
- if (WARN_ON(!dmabuf || !dev))
+ if (WARN_ON(!dmabuf || !info->dev))
return ERR_PTR(-EINVAL);
attach = kzalloc(sizeof(*attach), GFP_KERNEL);
if (!attach)
return ERR_PTR(-ENOMEM);
- attach->dev = dev;
+ attach->dev = info->dev;
attach->dmabuf = dmabuf;
mutex_lock(&dmabuf->lock);
@@ -688,9 +689,9 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
if (attach->sgt)
return attach->sgt;
- sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
- if (!sg_table)
- sg_table = ERR_PTR(-ENOMEM);
+ reservation_object_lock(attach->dmabuf->resv, NULL);
+ sg_table = dma_buf_map_attachment_locked(attach, direction);
+ reservation_object_unlock(attach->dmabuf->resv);
return sg_table;
}
@@ -744,8 +745,9 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
if (attach->sgt == sg_table)
return;
- attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
- direction);
+ reservation_object_lock(attach->dmabuf->resv, NULL);
+ dma_buf_unmap_attachment_locked(attach, sg_table, direction);
+ reservation_object_unlock(attach->dmabuf->resv);
}
EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
diff --git a/drivers/gpu/drm/armada/armada_gem.c b/drivers/gpu/drm/armada/armada_gem.c
index 642d0e70d0f8..19c47821032f 100644
--- a/drivers/gpu/drm/armada/armada_gem.c
+++ b/drivers/gpu/drm/armada/armada_gem.c
@@ -501,6 +501,10 @@ armada_gem_prime_export(struct drm_device *dev, struct drm_gem_object *obj,
struct drm_gem_object *
armada_gem_prime_import(struct drm_device *dev, struct dma_buf *buf)
{
+ struct dma_buf_attach_info attach_info = {
+ .dev = dev->dev,
+ .dmabuf = buf
+ };
struct dma_buf_attachment *attach;
struct armada_gem_object *dobj;
@@ -516,7 +520,7 @@ armada_gem_prime_import(struct drm_device *dev, struct dma_buf *buf)
}
}
- attach = dma_buf_attach(buf, dev->dev);
+ attach = dma_buf_attach(&attach_info);
if (IS_ERR(attach))
return ERR_CAST(attach);
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 231e3f6d5f41..1fadf5d5ed33 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -709,6 +709,10 @@ struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
struct dma_buf *dma_buf,
struct device *attach_dev)
{
+ struct dma_buf_attach_info attach_info = {
+ .dev = attach_dev,
+ .dmabuf = dma_buf
+ };
struct dma_buf_attachment *attach;
struct sg_table *sgt;
struct drm_gem_object *obj;
@@ -729,7 +733,7 @@ struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
if (!dev->driver->gem_prime_import_sg_table)
return ERR_PTR(-EINVAL);
- attach = dma_buf_attach(dma_buf, attach_dev);
+ attach = dma_buf_attach(&attach_info);
if (IS_ERR(attach))
return ERR_CAST(attach);
diff --git a/drivers/gpu/drm/i915/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
index 82e2ca17a441..aa7f685bd6ca 100644
--- a/drivers/gpu/drm/i915/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
@@ -277,6 +277,10 @@ static const struct drm_i915_gem_object_ops i915_gem_object_dmabuf_ops = {
struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev,
struct dma_buf *dma_buf)
{
+ struct dma_buf_attach_info attach_info = {
+ .dev = dev->dev,
+ .dmabuf = dma_buf
+ };
struct dma_buf_attachment *attach;
struct drm_i915_gem_object *obj;
int ret;
@@ -295,7 +299,7 @@ struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev,
}
/* need to attach */
- attach = dma_buf_attach(dma_buf, dev->dev);
+ attach = dma_buf_attach(&attach_info);
if (IS_ERR(attach))
return ERR_CAST(attach);
diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
index 4f80100ff5f3..8e6b6c879add 100644
--- a/drivers/gpu/drm/tegra/gem.c
+++ b/drivers/gpu/drm/tegra/gem.c
@@ -332,6 +332,10 @@ struct tegra_bo *tegra_bo_create_with_handle(struct drm_file *file,
static struct tegra_bo *tegra_bo_import(struct drm_device *drm,
struct dma_buf *buf)
{
+ struct dma_buf_attach_info attach_info = {
+ .dev = drm->dev,
+ .dmabuf = buf
+ };
struct tegra_drm *tegra = drm->dev_private;
struct dma_buf_attachment *attach;
struct tegra_bo *bo;
@@ -341,7 +345,7 @@ static struct tegra_bo *tegra_bo_import(struct drm_device *drm,
if (IS_ERR(bo))
return bo;
- attach = dma_buf_attach(buf, drm->dev);
+ attach = dma_buf_attach(&attach_info);
if (IS_ERR(attach)) {
err = PTR_ERR(attach);
goto free;
diff --git a/drivers/gpu/drm/udl/udl_dmabuf.c b/drivers/gpu/drm/udl/udl_dmabuf.c
index 556f62662aa9..86b928f9742f 100644
--- a/drivers/gpu/drm/udl/udl_dmabuf.c
+++ b/drivers/gpu/drm/udl/udl_dmabuf.c
@@ -226,6 +226,10 @@ static int udl_prime_create(struct drm_device *dev,
struct drm_gem_object *udl_gem_prime_import(struct drm_device *dev,
struct dma_buf *dma_buf)
{
+ struct dma_buf_attach_info attach_info = {
+ .dev = dev->dev,
+ .dmabuf = dma_buf
+ };
struct dma_buf_attachment *attach;
struct sg_table *sg;
struct udl_gem_object *uobj;
@@ -233,7 +237,7 @@ struct drm_gem_object *udl_gem_prime_import(struct drm_device *dev,
/* need to attach */
get_device(dev->dev);
- attach = dma_buf_attach(dma_buf, dev->dev);
+ attach = dma_buf_attach(&attach_info);
if (IS_ERR(attach)) {
put_device(dev->dev);
return ERR_CAST(attach);
diff --git a/drivers/media/common/videobuf2/videobuf2-dma-contig.c b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
index aff0ab7bf83d..1f2687b5eb0e 100644
--- a/drivers/media/common/videobuf2/videobuf2-dma-contig.c
+++ b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
@@ -676,6 +676,10 @@ static void vb2_dc_detach_dmabuf(void *mem_priv)
static void *vb2_dc_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
unsigned long size, enum dma_data_direction dma_dir)
{
+ struct dma_buf_attach_info attach_info = {
+ .dev = dev,
+ .dmabuf = dbuf
+ };
struct vb2_dc_buf *buf;
struct dma_buf_attachment *dba;
@@ -691,7 +695,7 @@ static void *vb2_dc_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
buf->dev = dev;
/* create attachment for the dmabuf with the user device */
- dba = dma_buf_attach(dbuf, buf->dev);
+ dba = dma_buf_attach(&attach_info);
if (IS_ERR(dba)) {
pr_err("failed to attach dmabuf\n");
kfree(buf);
diff --git a/drivers/media/common/videobuf2/videobuf2-dma-sg.c b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
index 015e737095cd..cbd626d2393a 100644
--- a/drivers/media/common/videobuf2/videobuf2-dma-sg.c
+++ b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
@@ -608,6 +608,10 @@ static void vb2_dma_sg_detach_dmabuf(void *mem_priv)
static void *vb2_dma_sg_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
unsigned long size, enum dma_data_direction dma_dir)
{
+ struct dma_buf_attach_info attach_info = {
+ .dev = dev,
+ .dmabuf = dbuf
+ };
struct vb2_dma_sg_buf *buf;
struct dma_buf_attachment *dba;
@@ -623,7 +627,7 @@ static void *vb2_dma_sg_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
buf->dev = dev;
/* create attachment for the dmabuf with the user device */
- dba = dma_buf_attach(dbuf, buf->dev);
+ dba = dma_buf_attach(&attach_info);
if (IS_ERR(dba)) {
pr_err("failed to attach dmabuf\n");
kfree(buf);
diff --git a/drivers/staging/media/tegra-vde/tegra-vde.c b/drivers/staging/media/tegra-vde/tegra-vde.c
index aa6c6bba961e..5a10c1facc27 100644
--- a/drivers/staging/media/tegra-vde/tegra-vde.c
+++ b/drivers/staging/media/tegra-vde/tegra-vde.c
@@ -568,6 +568,10 @@ static int tegra_vde_attach_dmabuf(struct device *dev,
size_t *size,
enum dma_data_direction dma_dir)
{
+ struct dma_buf_attach_info attach_info = {
+ .dev = dev,
+ .dmabuf = dmabuf
+ };
struct dma_buf_attachment *attachment;
struct dma_buf *dmabuf;
struct sg_table *sgt;
@@ -591,7 +595,7 @@ static int tegra_vde_attach_dmabuf(struct device *dev,
return -EINVAL;
}
- attachment = dma_buf_attach(dmabuf, dev);
+ attachment = dma_buf_attach(&attach_info);
if (IS_ERR(attachment)) {
dev_err(dev, "Failed to attach dmabuf\n");
err = PTR_ERR(attachment);
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 18a78be53541..7e23758db3a4 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -128,6 +128,9 @@ 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
+ * no_sgt_cache is true.
+ *
* Returns:
*
* A &sg_table scatter list of or the backing storage of the DMA buffer,
@@ -148,6 +151,9 @@ struct dma_buf_ops {
* It should also unpin the backing storage if this is the last mapping
* of the DMA buffer, it the exporter supports backing storage
* migration.
+ *
+ * This is always called with the dmabuf->resv object locked when
+ * no_sgt_cache is true.
*/
void (*unmap_dma_buf)(struct dma_buf_attachment *,
struct sg_table *,
@@ -370,6 +376,19 @@ struct dma_buf_export_info {
struct dma_buf_export_info name = { .exp_name = KBUILD_MODNAME, \
.owner = THIS_MODULE }
+/**
+ * struct dma_buf_attach_info - holds information needed to attach to a dma_buf
+ * @dmabuf: the exported dma_buf
+ * @dev: the device which wants to import the attachment
+ *
+ * This structure holds the information required to attach to a buffer. Used
+ * with dma_buf_attach() only.
+ */
+struct dma_buf_attach_info {
+ struct dma_buf *dmabuf;
+ struct device *dev;
+};
+
/**
* get_dma_buf - convenience wrapper for get_file.
* @dmabuf: [in] pointer to dma_buf
@@ -384,8 +403,8 @@ static inline void get_dma_buf(struct dma_buf *dmabuf)
get_file(dmabuf->file);
}
-struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
- struct device *dev);
+struct dma_buf_attachment *
+dma_buf_attach(const struct dma_buf_attach_info *info);
void dma_buf_detach(struct dma_buf *dmabuf,
struct dma_buf_attachment *dmabuf_attach);
--
2.17.1

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