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

Gustavo Padovan
2018-06-22T10:04:16Z

Hi Akhil,

On Fri, 2018-06-22 at 15:10 +0530, Akhil P Oommen wrote:
> 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);

Do we still need to export the symbol, it won't be called from outside
anymore? Other than that looks good to me:

Reviewed-by: Gustavo Padovan <gustavo.padovan@collabora.com>

Gustavo