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 <AlexBin.Xie at amd.com>
>> ---
>> 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,
>
>
