On Fri, Jun 22, 2018 at 11:08:48AM +0100, Chris Wilson wrote:
Quoting Gustavo Padovan (2018-06-22 11:04:16)
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:
There's a big drawback in that a module reference is often insufficient, and that a reference on the driver (or whatever is required for the lifetime of the fence) will already hold the module reference.
Considering that we want a few 100k fences in flight per second, is there no other way to only export a fence with a module reference?
We'd need to make the timeline a full-blown object (Maarten owes me one for that design screw-up), and then we could stuff all these things in there.
And I think that's the right fix, since try_module_get for every dma_fence_init just ain't cool really :-) -Daniel