dma-buf: add ref counting for module as exporter

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

1 files changed, 9 insertions, 1 deletions

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index c5a9138a6a8d..63a9914e42b8 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -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;