If we call into the shrinker for direct relcaim inside kmalloc, it will
retire the requests. If we retire the vma->last_active while a new
i915_vma_move_to_active() we can upset the delicate bookkeeping required
for the cache. After the possible invocation of the shrinker, we need to
double check the vma->last_active is still valid.

Fixes: 8b293eb53a7d ("drm/i915: Track the last-active inside the i915_vma")
Signed-off-by: Chris Wilson <[email protected]>
Cc: Tvrtko Ursulin <[email protected]>
---
 drivers/gpu/drm/i915/i915_vma.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index ed4e0fb558f7..11d834f94220 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -942,6 +942,14 @@ static struct i915_gem_active *active_instance(struct 
i915_vma *vma, u64 idx)
        }
 
        active = kmalloc(sizeof(*active), GFP_KERNEL);
+
+       /* kmalloc may retire the vma->last_active request (thanks shrinker)! */
+       if (unlikely(!i915_gem_active_raw(&vma->last_active,
+                                         &vma->vm->i915->drm.struct_mutex))) {
+               kfree(active);
+               goto out;
+       }
+
        if (unlikely(!active))
                return ERR_PTR(-ENOMEM);
 
-- 
2.18.0

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