On 2022/4/26 22:55, Andrey Grodzovsky wrote:
On 2022-04-25 22:54, Hangyu Hua wrote:
On 2022/4/25 23:42, Andrey Grodzovsky wrote:
On 2022-04-25 04:36, Hangyu Hua wrote:
When drm_sched_job_add_dependency() fails, dma_fence_put() will be
called
internally. Calling it again after drm_sched_job_add_dependency()
finishes
may result in a dangling pointer.
Fix this by removing redundant dma_fence_put().
Signed-off-by: Hangyu Hua <hbh25y@xxxxxxxxx>
---
drivers/gpu/drm/lima/lima_gem.c | 1 -
drivers/gpu/drm/scheduler/sched_main.c | 1 -
2 files changed, 2 deletions(-)
diff --git a/drivers/gpu/drm/lima/lima_gem.c
b/drivers/gpu/drm/lima/lima_gem.c
index 55bb1ec3c4f7..99c8e7f6bb1c 100644
--- a/drivers/gpu/drm/lima/lima_gem.c
+++ b/drivers/gpu/drm/lima/lima_gem.c
@@ -291,7 +291,6 @@ static int lima_gem_add_deps(struct drm_file
*file, struct lima_submit *submit)
err = drm_sched_job_add_dependency(&submit->task->base,
fence);
if (err) {
- dma_fence_put(fence);
return err;
Makes sense here
}
}
diff --git a/drivers/gpu/drm/scheduler/sched_main.c
b/drivers/gpu/drm/scheduler/sched_main.c
index b81fceb0b8a2..ebab9eca37a8 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -708,7 +708,6 @@ int
drm_sched_job_add_implicit_dependencies(struct drm_sched_job *job,
dma_fence_get(fence);
ret = drm_sched_job_add_dependency(job, fence);
if (ret) {
- dma_fence_put(fence);
Not sure about this one since if you look at the relevant commits -
'drm/scheduler: fix drm_sched_job_add_implicit_dependencies' and
'drm/scheduler: fix drm_sched_job_add_implicit_dependencies harder'
You will see that the dma_fence_put here balances the extra
dma_fence_get
above
Andrey
I don't think so. I checked the call chain and found no additional
dma_fence_get(). But dma_fence_get() needs to be called before
drm_sched_job_add_dependency() to keep the counter balanced.
I don't say there is an additional get, I just say that
drm_sched_job_add_dependency doesn't grab an extra reference to the
fences it stores so this needs to be done outside and for that
drm_sched_job_add_implicit_dependencies->dma_fence_get is called and, if
this addition fails you just call dma_fence_put to keep the counter
balanced.
drm_sched_job_add_implicit_dependencies() will call
drm_sched_job_add_dependency(). And drm_sched_job_add_dependency()
already call dma_fence_put() when it fails. Calling dma_fence_put()
twice doesn't make sense.
dma_fence_get() is in [2]. But dma_fence_put() will be called in [1] and
[3] when xa_alloc() fails.
int drm_sched_job_add_dependency(struct drm_sched_job *job,
struct dma_fence *fence)
{
...
ret = xa_alloc(&job->dependencies, &id, fence, xa_limit_32b, GFP_KERNEL);
if (ret != 0)
dma_fence_put(fence); <--- [1]
return ret;
}
EXPORT_SYMBOL(drm_sched_job_add_dependency);
int drm_sched_job_add_implicit_dependencies(struct drm_sched_job *job,
struct drm_gem_object *obj,
bool write)
{
struct dma_resv_iter cursor;
struct dma_fence *fence;
int ret;
dma_resv_for_each_fence(&cursor, obj->resv, write, fence) {
/* Make sure to grab an additional ref on the added fence */
dma_fence_get(fence); <--- [2]
ret = drm_sched_job_add_dependency(job, fence);
if (ret) {
dma_fence_put(fence); <--- [3]
return ret;
}
}
return 0;
}
On the other hand, dma_fence_get() and dma_fence_put() are meaningless
here if threre is an extra dma_fence_get() beacause counter will not
decrease to 0 during drm_sched_job_add_dependency().
I check the call chain as follows:
msm_ioctl_gem_submit()
-> submit_fence_sync()
-> drm_sched_job_add_implicit_dependencies()
Can you maybe trace or print one such example of problematic refcount
that you are trying to fix ? I still don't see where is the problem.
Andrey
I also wish I could. System logs can make this easy. But i don't have a
corresponding GPU physical device.
drm_sched_job_add_implicit_dependencies is only used in a few devices.
Thanks.
Thanks,
Hangyu
return ret;
}
}
