From aed44cbeae2b7674cd155ba5cc6506aafe46a94e Mon Sep 17 00:00:00 2001
From: Boris Brezillon <boris.brezillon@collabora.com>
Date: Fri, 29 Nov 2019 14:59:04 +0100
Subject: drm/panfrost: Fix a race in panfrost_gem_free_object()
Git-commit: aed44cbeae2b7674cd155ba5cc6506aafe46a94e
Patch-mainline: v5.5-rc2
References: bsc#1152489

panfrost_gem_shrinker_scan() might purge a BO (release the sgt and
kill the GPU mapping) that's being freed by panfrost_gem_free_object()
if we don't remove the BO from the shrinker list at the beginning of
panfrost_gem_free_object().

Fixes: 013b65101315 ("drm/panfrost: Add madvise and shrinker support")
Cc: <stable@vger.kernel.org>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Acked-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191129135908.2439529-5-boris.brezillon@collabora.com
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/panfrost/panfrost_gem.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
index deca0c30bbd4..fa1b2732a3a8 100644
--- a/drivers/gpu/drm/panfrost/panfrost_gem.c
+++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
@@ -19,6 +19,16 @@ static void panfrost_gem_free_object(struct drm_gem_object *obj)
 	struct panfrost_gem_object *bo = to_panfrost_bo(obj);
 	struct panfrost_device *pfdev = obj->dev->dev_private;
 
+	/*
+	 * Make sure the BO is no longer inserted in the shrinker list before
+	 * taking care of the destruction itself. If we don't do that we have a
+	 * race condition between this function and what's done in
+	 * panfrost_gem_shrinker_scan().
+	 */
+	mutex_lock(&pfdev->shrinker_lock);
+	list_del_init(&bo->base.madv_list);
+	mutex_unlock(&pfdev->shrinker_lock);
+
 	if (bo->sgts) {
 		int i;
 		int n_sgt = bo->base.base.size / SZ_2M;
@@ -33,11 +43,6 @@ static void panfrost_gem_free_object(struct drm_gem_object *obj)
 		kfree(bo->sgts);
 	}
 
-	mutex_lock(&pfdev->shrinker_lock);
-	if (!list_empty(&bo->base.madv_list))
-		list_del(&bo->base.madv_list);
-	mutex_unlock(&pfdev->shrinker_lock);
-
 	drm_gem_shmem_free_object(obj);
 }
 
-- 
2.28.0