[PATCH v2] dma-buf/fence: Take refcount on the module that owns the fence

Akhil P Oommen
2018-06-22T09:40:07Z

Each fence object holds function pointers of the module that initialized
it. Allowing the module to unload before this fence's release is
catastrophic. So, keep a refcount on the module until the fence is
released.

Signed-off-by: Akhil P Oommen <akhilpo@codeaurora.org>
---
Changes in v2:
- added description for the new function parameter.

drivers/dma-buf/dma-fence.c | 16 +++++++++++++---
include/linux/dma-fence.h | 10 ++++++++--
2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index 4edb9fd..2aaa44e 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -18,6 +18,7 @@
* more details.
*/

+#include <linux/module.h>
#include <linux/slab.h>
#include <linux/export.h>
#include <linux/atomic.h>
@@ -168,6 +169,7 @@ void dma_fence_release(struct kref *kref)
{
struct dma_fence *fence =
container_of(kref, struct dma_fence, refcount);
+ struct module *module = fence->owner;

trace_dma_fence_destroy(fence);

@@ -178,6 +180,8 @@ void dma_fence_release(struct kref *kref)
fence->ops->release(fence);
else
dma_fence_free(fence);
+
+ module_put(module);
}
EXPORT_SYMBOL(dma_fence_release);

@@ -541,6 +545,7 @@ struct default_wait_cb {

/**
* dma_fence_init - Initialize a custom fence.
+ * @module: [in] the module that calls this API
* @fence: [in] the fence to initialize
* @ops: [in] the dma_fence_ops for operations on this fence
* @lock: [in] the irqsafe spinlock to use for locking this fence
@@ -556,8 +561,9 @@ struct default_wait_cb {
* to check which fence is later by simply using dma_fence_later.
*/
void
-dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
- spinlock_t *lock, u64 context, unsigned seqno)
+_dma_fence_init(struct module *module, struct dma_fence *fence,
+ const struct dma_fence_ops *ops, spinlock_t *lock,
+ u64 context, unsigned seqno)
{
BUG_ON(!lock);
BUG_ON(!ops || !ops->wait || !ops->enable_signaling ||
@@ -571,7 +577,11 @@ struct default_wait_cb {
fence->seqno = seqno;
fence->flags = 0UL;
fence->error = 0;
+ fence->owner = module;
+
+ if (!try_module_get(module))
+ fence->owner = NULL;

trace_dma_fence_init(fence);
}
-EXPORT_SYMBOL(dma_fence_init);
+EXPORT_SYMBOL(_dma_fence_init);
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index eb9b05a..8159125 100644
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -36,6 +36,8 @@

/**
* struct dma_fence - software synchronization primitive
+ * @owner: the module that contains fence_ops functions.
+ * Usually THIS_MODULE.
* @refcount: refcount for this fence
* @ops: dma_fence_ops associated with this fence
* @rcu: used for releasing fence with kfree_rcu
@@ -71,6 +73,7 @@
* been completed, or never called at all.
*/
struct dma_fence {
+ struct module *owner;
struct kref refcount;
const struct dma_fence_ops *ops;
struct rcu_head rcu;
@@ -249,8 +252,11 @@ struct dma_fence_ops {
char *str, int size);
};

-void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
- spinlock_t *lock, u64 context, unsigned seqno);
+#define dma_fence_init(fence, ops, lock, context, seqno) _dma_fence_init( \
+ THIS_MODULE, fence, ops, lock, context, seqno)
+void _dma_fence_init(struct module *module, struct dma_fence *fence,
+ const struct dma_fence_ops *ops, spinlock_t *lock, u64 context,
+ unsigned seqno);

void dma_fence_release(struct kref *kref);
void dma_fence_free(struct dma_fence *fence);
--
1.9.1