[Intel-xe] [PATCH 2/2] drm/xe: Properly remove the vma from the vm::notifer::rebind_list when destroyed

[Thomas Hellström]

On 5/11/23 16:54, Matthew Brost wrote:
> On Wed, May 10, 2023 at 04:19:32PM +0200, Thomas Hellström wrote:
>> If a vma was destroyed with the bo evicted, it might happen that we forget
>> to remove it from the notifer::rebind_list. Fix to make sure that really
>> happens.
>>
>> Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
>> ---
>>   drivers/gpu/drm/xe/xe_vm.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
>> index 5f93d78c2e58..f54b3b7566c9 100644
>> --- a/drivers/gpu/drm/xe/xe_vm.c
>> +++ b/drivers/gpu/drm/xe/xe_vm.c
>> @@ -978,6 +978,15 @@ static void xe_vma_destroy(struct xe_vma *vma, struct dma_fence *fence)
>>   	} else {
>>   		xe_bo_assert_held(vma->bo);
>>   		list_del(&vma->bo_link);
>> +		/*
>> +		 * TODO: We can do an advisory check for list link empty here,
>> +		 * if this lock becomes too costly. Nobody can re-add to the
>> +		 * bo to the vm::notifier::rebind_list at this point since we
>> +		 * have the bo lock.
>> +		 */
> IMO grab isn't a big deal, not sure this is worth such a lengthly comment.

Ok, I'll remove it.


>
>> +		 spin_lock(&vm->notifier.list_lock);
>> +		 list_del(&vma->notifier.rebind_link);
> Can you safe call list_del on an empty list? I thought that call blows
> up hence we have a bunch of if (!list_empty()) checks before calling
> list_del all over the driver.

Good question. Looking at the implementation it definitely looks 
possible, and I have LIST_DEBUG turned on when testing, so I assume it 
would have blown up otherwise.

/Thomas


>
> Matt
>
>> +		 spin_unlock(&vm->notifier.list_lock);
>>   		if (!vma->bo->vm)
>>   			vm_remove_extobj(vma);
>>   	}
>> -- 
>> 2.39.2
>>