linux-kernel - [PATCH 5.9 001/255] drm/i915: Hold onto an explicit ref to i915_vma

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Date:   Tue, 17 Nov 2020 14:02:21 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.9 001/255] drm/i915: Hold onto an explicit ref to i915_vma_work.pinned

From: Chris Wilson <chris@...is-wilson.co.uk>

[ Upstream commit 537457a979a02a410b555fab289dcb28b588f33b ]

Since __vma_release is run by a kworker after the fence has been
signaled, it is no longer protected by the active reference on the vma,
and so the alias of vw->pinned to vma->obj is also not protected by a
reference on the object. Add an explicit reference for vw->pinned so it
will always be safe.

Found by inspection.

Fixes: 54d7195f8c64 ("drm/i915: Unpin vma->obj on early error")
Reported-by: Tvrtko Ursulin <tvrtko.ursulin@...el.com>
Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@...el.com>
Cc: <stable@...r.kernel.org> # v5.6+
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@...el.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201102161931.30031-1-chris@chris-wilson.co.uk
(cherry picked from commit bc73e5d33048b7ab5f12b11b5d923700467a8e1d)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@...el.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/i915/i915_vma.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index bc64f773dcdb4..034d0a8d24c8c 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -315,8 +315,10 @@ static void __vma_release(struct dma_fence_work *work)
 {
 	struct i915_vma_work *vw = container_of(work, typeof(*vw), base);
 
-	if (vw->pinned)
+	if (vw->pinned) {
 		__i915_gem_object_unpin_pages(vw->pinned);
+		i915_gem_object_put(vw->pinned);
+	}
 }
 
 static const struct dma_fence_work_ops bind_ops = {
@@ -430,7 +432,7 @@ int i915_vma_bind(struct i915_vma *vma,
 
 		if (vma->obj) {
 			__i915_gem_object_pin_pages(vma->obj);
-			work->pinned = vma->obj;
+			work->pinned = i915_gem_object_get(vma->obj);
 		}
 	} else {
 		ret = vma->ops->bind_vma(vma->vm, vma, cache_level, bind_flags);
-- 
2.27.0