linux-kernel - [PATCH] drm/i915: Fix race in __i915_vma_remove

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Message-Id: <20220419234436.2638649-1-kherbst@redhat.com>
Date:   Wed, 20 Apr 2022 01:44:36 +0200
From:   Karol Herbst <kherbst@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Karol Herbst <kherbst@...hat.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: [PATCH] drm/i915: Fix race in __i915_vma_remove_closed

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.

Cc: Chris Wilson <chris@...is-wilson.co.uk>
Cc: intel-gfx@...ts.freedesktop.org
Cc: dri-devel@...ts.freedesktop.org
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5732
Signed-off-by: Karol Herbst <kherbst@...hat.com>
---
 drivers/gpu/drm/i915/i915_vma.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index 162e8d83691b..bb3b6e4bee8b 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)
@@ -1651,7 +1651,11 @@ static void release_references(struct i915_vma *vma, bool vm_ddestroy)
 
 	spin_unlock(&obj->vma.lock);
 
+	struct intel_gt *gt = vma->vm->gt;
+
+	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