Re: Kernel/driver hacking: panic: Assertion vm_object_busied((m->object)) failed at /usr/src/sys/vm/vm_page.c:5455

Hi Neel,

On 6/16/21 5:28 PM, Neel Chauhan wrote:
> Hi,
> 
> On 2021-06-16 00:35, Hans Petter Selasky wrote:
>> Do you have the full backtrace?
> 
> Yes.
> 
> I have attached a stack trace in the previous email, but if you didn't 
> get it, I have uploaded it to GitHub: 
> https://gist.github.com/neelchauhan/437bd10239f84c563aafb37ab440029a
> 
>> Doesn't this code work in the current DRM - kmod? What changed? Did
>> you perhaps miss a patch?
> 
> I think there is new code with Linux 5.6 which changes how this is done.
> 
> I have been attempting to make a FreeBSD equivalent, but it panics. It 
> is **not** from missing Linux commits since I believe I added them all.
> 
> The code in my GH repo: 
> https://github.com/neelchauhan/drm-kmod/blob/5.7-wip/drivers/gpu/drm/i915/gem/i915_gem_mman.c#L346 
> 

I think the following changes are needed. CC'ing Jeff.


> 	for_each_sg_page(pages->sgl, &sg_iter, pages->nents, 0) {
> 		pmap_t pmap = vm_map_pmap(map);
> 		struct vm_page *pa = sg_page_iter_page(&sg_iter);
> 		VM_OBJECT_RLOCK(pa->object);

Try adding this:
		vm_object_busy(pa->object);

> 		if (pmap_enter(pmap, va, pa, 0, flags, 0)) {

Try adding this:
		vm_object_unbusy(pa->object);
		VM_OBJECT_RUNLOCK(pa->object);

> 			err = -ENOMEM;
> 			break;
> 		}
Try adding this:
		vm_object_unbusy(pa->object);

> 		VM_OBJECT_RUNLOCK(pa->object);
> 		va += PAGE_SIZE;

--HPS