[Intel-gfx] [PATCH] drm/i915: Handle recursive shrinker for vma->last_active allocation

[Chris Wilson]

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 <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 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