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Subject[PATCH 5.4 45/80] drm/panfrost: Fix a race in panfrost_gem_free_object()
Date
From: Boris Brezillon <boris.brezillon@collabora.com>

commit aed44cbeae2b7674cd155ba5cc6506aafe46a94e upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/gpu/drm/panfrost/panfrost_gem.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)

--- 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(str
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(str
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);
}


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