[PATCH v2] drm/i915: Fix race in __i915_vma_remove_closed

[Karol Herbst]

i915_vma_reopen checked if the vma is closed before without taking the
lock. So multiple threads could attempt removing the vma.

Instead the lock needs to be taken before actually checking.

v2: move struct declaration

Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: intel-gfx at lists.freedesktop.org
Cc: dri-devel at lists.freedesktop.org
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5732
Signed-off-by: Karol Herbst <kherbst at redhat.com>
---
 drivers/gpu/drm/i915/i915_vma.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index 162e8d83691b..2efdad2b43fa 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -1615,17 +1615,17 @@ void i915_vma_close(struct i915_vma *vma)
 
 static void __i915_vma_remove_closed(struct i915_vma *vma)
 {
-	struct intel_gt *gt = vma->vm->gt;
-
-	spin_lock_irq(&gt->closed_lock);
 	list_del_init(&vma->closed_link);
-	spin_unlock_irq(&gt->closed_lock);
 }
 
 void i915_vma_reopen(struct i915_vma *vma)
 {
+	struct intel_gt *gt = vma->vm->gt;
+
+	spin_lock_irq(&gt->closed_lock);
 	if (i915_vma_is_closed(vma))
 		__i915_vma_remove_closed(vma);
+	spin_unlock_irq(&gt->closed_lock);
 }
 
 static void force_unbind(struct i915_vma *vma)
@@ -1641,6 +1641,7 @@ static void force_unbind(struct i915_vma *vma)
 static void release_references(struct i915_vma *vma, bool vm_ddestroy)
 {
 	struct drm_i915_gem_object *obj = vma->obj;
+	struct intel_gt *gt = vma->vm->gt;
 
 	GEM_BUG_ON(i915_vma_is_active(vma));
 
@@ -1651,7 +1652,9 @@ static void release_references(struct i915_vma *vma, bool vm_ddestroy)
 
 	spin_unlock(&obj->vma.lock);
 
+	spin_lock_irq(&gt->closed_lock);
 	__i915_vma_remove_closed(vma);
+	spin_unlock_irq(&gt->closed_lock);
 
 	if (vm_ddestroy)
 		i915_vm_resv_put(vma->vm);
-- 
2.35.1