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dma-buf: add ref counting for module as exporter

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Add reference counting on a kernel module that exports dma-buf and
implements its operations. This prevents the module from being unloaded
while DMABUF file is in use.

The original patch [1] was submitted by Tomasz Stanislawski, but this
is a simpler way to do it.

v3: call module_put() as late as possible, per gregkh's comment.
v2: move owner to struct dma_buf, and use DEFINE_DMA_BUF_EXPORT_INFO
    macro to simplify the change.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>

[1]: https://lkml.org/lkml/2012/8/8/163
This commit is contained in:
Sumit Semwal 2015-05-05 14:56:15 +05:30
parent 5ebe6afaf0
commit 9abdffe286
2 changed files with 17 additions and 3 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

10
drivers/dma-buf/dma-buf.c
View file

@ -29,6 +29,7 @@
#include <linux/anon_inodes.h>
#include <linux/export.h>
#include <linux/debugfs.h>
#include <linux/module.h>
#include <linux/seq_file.h>
#include <linux/poll.h>
#include <linux/reservation.h>
@ -72,6 +73,7 @@ static int dma_buf_release(struct inode *inode, struct file *file)
if (dmabuf->resv == (struct reservation_object *)&dmabuf[1])
reservation_object_fini(dmabuf->resv);
module_put(dmabuf->owner);
kfree(dmabuf);
return 0;
}
@ -302,14 +304,20 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
return ERR_PTR(-EINVAL);
}
if (!try_module_get(exp_info->owner))
return ERR_PTR(-ENOENT);
dmabuf = kzalloc(alloc_size, GFP_KERNEL);
if (dmabuf == NULL)
if (!dmabuf) {
module_put(exp_info->owner);
return ERR_PTR(-ENOMEM);
}
dmabuf->priv = exp_info->priv;
dmabuf->ops = exp_info->ops;
dmabuf->size = exp_info->size;
dmabuf->exp_name = exp_info->exp_name;
dmabuf->owner = exp_info->owner;
init_waitqueue_head(&dmabuf->poll);
dmabuf->cb_excl.poll = dmabuf->cb_shared.poll = &dmabuf->poll;
dmabuf->cb_excl.active = dmabuf->cb_shared.active = 0;

10
include/linux/dma-buf.h
View file

@ -115,6 +115,8 @@ struct dma_buf_ops {
* @attachments: list of dma_buf_attachment that denotes all devices attached.
* @ops: dma_buf_ops associated with this buffer object.
* @exp_name: name of the exporter; useful for debugging.
* @owner: pointer to exporter module; used for refcounting when exporter is a
* kernel module.
* @list_node: node for dma_buf accounting and debugging.
* @priv: exporter specific private data for this buffer object.
* @resv: reservation object linked to this dma-buf
@ -129,6 +131,7 @@ struct dma_buf {
unsigned vmapping_counter;
void *vmap_ptr;
const char *exp_name;
struct module *owner;
struct list_head list_node;
void *priv;
struct reservation_object *resv;
@ -164,7 +167,8 @@ struct dma_buf_attachment {
/**
* struct dma_buf_export_info - holds information needed to export a dma_buf
* @exp_name: name of the exporting module - useful for debugging.
* @exp_name: name of the exporter - useful for debugging.
* @owner: pointer to exporter module - used for refcounting kernel module
* @ops: Attach allocator-defined dma buf ops to the new buffer
* @size: Size of the buffer
* @flags: mode flags for the file
@ -176,6 +180,7 @@ struct dma_buf_attachment {
*/
struct dma_buf_export_info {
const char *exp_name;
struct module *owner;
const struct dma_buf_ops *ops;
size_t size;
int flags;
@ -187,7 +192,8 @@ struct dma_buf_export_info {
* helper macro for exporters; zeros and fills in most common values
*/
#define DEFINE_DMA_BUF_EXPORT_INFO(a) \
struct dma_buf_export_info a = { .exp_name = KBUILD_MODNAME }
struct dma_buf_export_info a = { .exp_name = KBUILD_MODNAME, \
.owner = THIS_MODULE }
/**
* get_dma_buf - convenience wrapper for get_file.