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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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