On 2017-06-12 07:00 PM, Christian König wrote:
Am 12.06.2017 um 22:31 schrieb Alex Xie:
This patch is to move a loop of unref BOs and
several memory free function calls out of
critical sections.
Signed-off-by: Alex Xie <[email protected]>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
index a664987..02c138f 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
@@ -75,9 +75,12 @@ static void amdgpu_bo_list_destroy(struct
amdgpu_fpriv *fpriv, int id)
/* Another user may have a reference to this list still */
mutex_lock(&list->lock);
mutex_unlock(&list->lock);
+ mutex_unlock(&fpriv->bo_list_lock);
amdgpu_bo_list_free(list);
}
- mutex_unlock(&fpriv->bo_list_lock);
+ else {
+ mutex_unlock(&fpriv->bo_list_lock);
+ }
You could move the unlock of bo_list_lock even before the if.
But since you pointed it out there is quite a bug in this function:
/* Another user may have a reference to this list
still */
mutex_lock(&list->lock);
mutex_unlock(&list->lock);
Not sure if that is still up to date, but that use case used to be
illegal with mutexes.
As I understand this piece of code, these mutex_lock and mutex_unlock
pair are used to make sure all other tasks have finished
access of the bo list. Another side of this story is in function
amdgpu_bo_list_get. These two piece of codes together make sure
we can safely destroy bo list.
Otherwise we can easily simplify these lockings.
Let me give an example here.
In function amdgpu_bo_list_get, assuming we change the code like this:
...
down_read(&fpriv->bo_list_lock);
result = idr_find(&fpriv->bo_list_handles, id);
up_read(&fpriv->bo_list_lock);
/**Line 1. Task A was scheduled away from CPU**/
if (result)
mutex_lock(&result->lock);
...
In function amdgpu_bo_list_destroy, assuming we change the code like this:
...
down_write(&fpriv->bo_list_lock);
list = idr_remove(&fpriv->bo_list_handles, id);
up_write(&fpriv->bo_list_lock);
if (list) {
/* Another user may have a reference to this list still */
mutex_lock(&list->lock);
mutex_unlock(&list->lock);
amdgpu_bo_list_free(list);
}
}
When task A is running in function amdgpu_bo_list_get in line 1, CPU
scheduler takes CPU away from task A.
Then Task B run function amdgpu_bo_list_destroy. Task B can run all the
way to destroy and free mutex.
Later Task A is back to run. The mutex result->lock has been destroyed
by task B. Now task A try to lock a mutex
which has been destroyed and freed.
Christian.
}
static int amdgpu_bo_list_set(struct amdgpu_device *adev,
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