[Intel-gfx] [PATCH] drm/i915/gem: Avoid waiting inside mmu_notifier_invalidate_range

[Chris Wilson]

Since the userptr may be invalidated from inside a reclaim path, we
cannot wait on unbinding the object as we may hold any number of locks,
including the active reference of the object we are trying to
invalidate. E.g.

[<0>] __i915_active_wait+0x70/0xc0 [i915]
[<0>] i915_vma_unbind+0x2f/0x110 [i915]
[<0>] i915_gem_object_unbind+0x17c/0x350 [i915]
[<0>] userptr_mn_invalidate_range_start+0xb6/0x140 [i915]
[<0>] __mmu_notifier_invalidate_range_start+0x105/0x150
[<0>] try_to_unmap_one+0x7fb/0x900
[<0>] rmap_walk_file+0xe4/0x240
[<0>] try_to_unmap+0x85/0xc0
[<0>] shrink_page_list+0x885/0xe80
[<0>] shrink_inactive_list+0x155/0x260
[<0>] shrink_lruvec+0x4ec/0x5f0
[<0>] shrink_node+0x15b/0x410
[<0>] try_to_free_pages+0x169/0x3a0
[<0>] __alloc_pages_slowpath.constprop.0+0x251/0xa00
[<0>] __alloc_pages_nodemask+0x144/0x170
[<0>] new_slab+0x259/0x280
[<0>] ___slab_alloc.isra.0.constprop.0+0x3dd/0x460
[<0>] __slab_alloc.isra.0.constprop.0+0x9/0x10
[<0>] kmem_cache_alloc+0x11a/0x130
[<0>] alloc_pd+0x17/0x60 [i915]
[<0>] __gen8_ppgtt_alloc+0x2d7/0x350 [i915]
[<0>] gen8_ppgtt_alloc+0x35/0x70 [i915]
[<0>] ppgtt_bind_vma+0x29/0x70 [i915]

This situation only occurs when the lru page shrinker tries to sacrifice
one the objects it is trying to allocate for. However, we do have to
wait for an active object so that we can revoke access to the page
range.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/1702
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index 8b0708708671..a398d817543e 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -126,9 +126,11 @@ userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
 		}
 		spin_unlock(&mn->lock);
 
-		ret = i915_gem_object_unbind(obj,
-					     I915_GEM_OBJECT_UNBIND_ACTIVE |
-					     I915_GEM_OBJECT_UNBIND_BARRIER);
+		ret = i915_gem_object_wait(obj,
+					   I915_WAIT_ALL,
+					   MAX_SCHEDULE_TIMEOUT);
+		if (ret == 0)
+			ret = i915_gem_object_unbind(obj, 0);
 		if (ret == 0)
 			ret = __i915_gem_object_put_pages(obj);
 		i915_gem_object_put(obj);
-- 
2.20.1