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Subject[PATCH] dma-buf: add reference counting for exporter module
This patch adds reference counting on a module that exports dma-buf and
implements its operations. This prevents the module from being unloaded while
DMABUF file is in use.

Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com>
---
Documentation/dma-buf-sharing.txt | 3 ++-
drivers/base/dma-buf.c | 10 +++++++++-
drivers/gpu/drm/exynos/exynos_drm_dmabuf.c | 1 +
drivers/gpu/drm/i915/i915_gem_dmabuf.c | 1 +
drivers/gpu/drm/nouveau/nouveau_prime.c | 1 +
drivers/gpu/drm/radeon/radeon_prime.c | 1 +
drivers/staging/omapdrm/omap_gem_dmabuf.c | 1 +
include/linux/dma-buf.h | 2 ++
8 files changed, 18 insertions(+), 2 deletions(-)
diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
index ad86fb8..2613057 100644
--- a/Documentation/dma-buf-sharing.txt
+++ b/Documentation/dma-buf-sharing.txt
@@ -49,7 +49,8 @@ The dma_buf buffer sharing API usage contains the following steps:
The buffer exporter announces its wish to export a buffer. In this, it
connects its own private buffer data, provides implementation for operations
that can be performed on the exported dma_buf, and flags for the file
- associated with this buffer.
+ associated with this buffer. The operations structure has owner field.
+ You should initialize this to THIS_MODULE in most cases.

Interface:
struct dma_buf *dma_buf_export(void *priv, struct dma_buf_ops *ops,
diff --git a/drivers/base/dma-buf.c b/drivers/base/dma-buf.c
index c30f3e1..d14b2f5 100644
--- a/drivers/base/dma-buf.c
+++ b/drivers/base/dma-buf.c
@@ -27,6 +27,7 @@
#include <linux/dma-buf.h>
#include <linux/anon_inodes.h>
#include <linux/export.h>
+#include <linux/module.h>

static inline int is_dma_buf_file(struct file *);

@@ -40,6 +41,7 @@ static int dma_buf_release(struct inode *inode, struct file *file)
dmabuf = file->private_data;

dmabuf->ops->release(dmabuf);
+ module_put(dmabuf->ops->owner);
kfree(dmabuf);
return 0;
}
@@ -96,6 +98,7 @@ struct dma_buf *dma_buf_export(void *priv, const struct dma_buf_ops *ops,
struct file *file;

if (WARN_ON(!priv || !ops
+ || !ops->owner
|| !ops->map_dma_buf
|| !ops->unmap_dma_buf
|| !ops->release
@@ -105,9 +108,14 @@ struct dma_buf *dma_buf_export(void *priv, const struct dma_buf_ops *ops,
return ERR_PTR(-EINVAL);
}

+ if (!try_module_get(ops->owner))
+ return ERR_PTR(-ENOENT);
+
dmabuf = kzalloc(sizeof(struct dma_buf), GFP_KERNEL);
- if (dmabuf == NULL)
+ if (dmabuf == NULL) {
+ module_put(ops->owner);
return ERR_PTR(-ENOMEM);
+ }

dmabuf->priv = priv;
dmabuf->ops = ops;
diff --git a/drivers/gpu/drm/exynos/exynos_drm_dmabuf.c b/drivers/gpu/drm/exynos/exynos_drm_dmabuf.c
index 613bf8a..cf3bc6d 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_dmabuf.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_dmabuf.c
@@ -164,6 +164,7 @@ static void exynos_gem_dmabuf_kunmap(struct dma_buf *dma_buf,
}

static struct dma_buf_ops exynos_dmabuf_ops = {
+ .owner = THIS_MODULE,
.map_dma_buf = exynos_gem_map_dma_buf,
.unmap_dma_buf = exynos_gem_unmap_dma_buf,
.kmap = exynos_gem_dmabuf_kmap,
diff --git a/drivers/gpu/drm/i915/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
index aa308e1..07ff03b 100644
--- a/drivers/gpu/drm/i915/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
@@ -152,6 +152,7 @@ static int i915_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *
}

static const struct dma_buf_ops i915_dmabuf_ops = {
+ .owner = THIS_MODULE,
.map_dma_buf = i915_gem_map_dma_buf,
.unmap_dma_buf = i915_gem_unmap_dma_buf,
.release = i915_gem_dmabuf_release,
diff --git a/drivers/gpu/drm/nouveau/nouveau_prime.c b/drivers/gpu/drm/nouveau/nouveau_prime.c
index a25cf2c..8605033 100644
--- a/drivers/gpu/drm/nouveau/nouveau_prime.c
+++ b/drivers/gpu/drm/nouveau/nouveau_prime.c
@@ -127,6 +127,7 @@ static void nouveau_gem_prime_vunmap(struct dma_buf *dma_buf, void *vaddr)
}

static const struct dma_buf_ops nouveau_dmabuf_ops = {
+ .owner = THIS_MODULE,
.map_dma_buf = nouveau_gem_map_dma_buf,
.unmap_dma_buf = nouveau_gem_unmap_dma_buf,
.release = nouveau_gem_dmabuf_release,
diff --git a/drivers/gpu/drm/radeon/radeon_prime.c b/drivers/gpu/drm/radeon/radeon_prime.c
index 6bef46a..4061fd3 100644
--- a/drivers/gpu/drm/radeon/radeon_prime.c
+++ b/drivers/gpu/drm/radeon/radeon_prime.c
@@ -127,6 +127,7 @@ static void radeon_gem_prime_vunmap(struct dma_buf *dma_buf, void *vaddr)
mutex_unlock(&dev->struct_mutex);
}
const static struct dma_buf_ops radeon_dmabuf_ops = {
+ .owner = THIS_MODULE,
.map_dma_buf = radeon_gem_map_dma_buf,
.unmap_dma_buf = radeon_gem_unmap_dma_buf,
.release = radeon_gem_dmabuf_release,
diff --git a/drivers/staging/omapdrm/omap_gem_dmabuf.c b/drivers/staging/omapdrm/omap_gem_dmabuf.c
index 42728e0..6a4dd67 100644
--- a/drivers/staging/omapdrm/omap_gem_dmabuf.c
+++ b/drivers/staging/omapdrm/omap_gem_dmabuf.c
@@ -179,6 +179,7 @@ out_unlock:
}

struct dma_buf_ops omap_dmabuf_ops = {
+ .owner = THIS_MODULE,
.map_dma_buf = omap_gem_map_dma_buf,
.unmap_dma_buf = omap_gem_unmap_dma_buf,
.release = omap_gem_dmabuf_release,
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index eb48f38..22953de 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -37,6 +37,7 @@ struct dma_buf_attachment;

/**
* struct dma_buf_ops - operations possible on struct dma_buf
+ * @owner: the module that implements dma_buf operations
* @attach: [optional] allows different devices to 'attach' themselves to the
* given buffer. It might return -EBUSY to signal that backing storage
* is already allocated and incompatible with the requirements
@@ -70,6 +71,7 @@ struct dma_buf_attachment;
* @vunmap: [optional] unmaps a vmap from the buffer
*/
struct dma_buf_ops {
+ struct module *owner;
int (*attach)(struct dma_buf *, struct device *,
struct dma_buf_attachment *);

--
1.7.9.5

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