[5.12 regression] ttm->pages NULL dereference with radeon driver

[Takashi Iwai]

Hi,

we've received a regression report showing NULL dereference Oops with
radeon driver on 5.12 kernel:
  https://bugzilla.opensuse.org/show_bug.cgi?id=1185516

It turned out that the recent TTM cleanup / refactoring via commit
0575ff3d33cd ("drm/radeon: stop using pages with
drm_prime_sg_to_page_addr_arrays v2") is the culprit.  On 5.12 kernel,
ttm->pages is no longer allocated / set up, while the radeon driver
still has a few places assuming the valid ttm->pages, and for the
reporter (running the modesettig driver), radeon_gart_bind() hits the
problem.

A hackish patch below was confirmed to work, at least, but obviously
we need a proper fix.

Could you take a look at it?


thanks,

Takashi

--- a/drivers/gpu/drm/radeon/radeon_gart.c
+++ b/drivers/gpu/drm/radeon/radeon_gart.c
@@ -253,7 +253,7 @@ void radeon_gart_unbind(struct radeon_de
 	t = offset / RADEON_GPU_PAGE_SIZE;
 	p = t / (PAGE_SIZE / RADEON_GPU_PAGE_SIZE);
 	for (i = 0; i < pages; i++, p++) {
-		if (rdev->gart.pages[p]) {
+		if (1 /*rdev->gart.pages[p]*/) {
 			rdev->gart.pages[p] = NULL;
 			for (j = 0; j < (PAGE_SIZE / RADEON_GPU_PAGE_SIZE); j++, t++) {
 				rdev->gart.pages_entry[t] = rdev->dummy_page.entry;
@@ -301,7 +301,7 @@ int radeon_gart_bind(struct radeon_devic
 	p = t / (PAGE_SIZE / RADEON_GPU_PAGE_SIZE);
 
 	for (i = 0; i < pages; i++, p++) {
-		rdev->gart.pages[p] = pagelist[i];
+		/* rdev->gart.pages[p] = pagelist[i]; */
 		page_base = dma_addr[i];
 		for (j = 0; j < (PAGE_SIZE / RADEON_GPU_PAGE_SIZE); j++, t++) {
 			page_entry = radeon_gart_get_page_entry(page_base, flags);
--- a/drivers/gpu/drm/radeon/radeon_ttm.c
+++ b/drivers/gpu/drm/radeon/radeon_ttm.c
@@ -360,6 +360,8 @@ static int radeon_ttm_tt_pin_userptr(str
 
 	if (current->mm != gtt->usermm)
 		return -EPERM;
+	if (!ttm->pages)
+		return -EPERM;
 
 	if (gtt->userflags & RADEON_GEM_USERPTR_ANONONLY) {
 		/* check that we only pin down anonymous memory