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
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index c5a9138..63a9914 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 @@
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 @@
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;