If 2 threads change the MADVISE property of the same BO in parallel we
might end up with an shmem->madv value that's inconsistent with the
presence of the BO in the shrinker list.

The easiest solution to fix that is to protect the
drm_gem_shmem_madvise() call with the shrinker lock.

Fixes: 013b65101315 ("drm/panfrost: Add madvise and shrinker support")
Cc: <sta...@vger.kernel.org>
Signed-off-by: Boris Brezillon <boris.brezil...@collabora.com>
---
 drivers/gpu/drm/panfrost/panfrost_drv.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c 
b/drivers/gpu/drm/panfrost/panfrost_drv.c
index f21bc8a7ee3a..efc0a24d1f4c 100644
--- a/drivers/gpu/drm/panfrost/panfrost_drv.c
+++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
@@ -347,20 +347,19 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, 
void *data,
                return -ENOENT;
        }
 
+       mutex_lock(&pfdev->shrinker_lock);
        args->retained = drm_gem_shmem_madvise(gem_obj, args->madv);
 
        if (args->retained) {
                struct panfrost_gem_object *bo = to_panfrost_bo(gem_obj);
 
-               mutex_lock(&pfdev->shrinker_lock);
-
                if (args->madv == PANFROST_MADV_DONTNEED)
-                       list_add_tail(&bo->base.madv_list, 
&pfdev->shrinker_list);
+                       list_add_tail(&bo->base.madv_list,
+                                     &pfdev->shrinker_list);
                else if (args->madv == PANFROST_MADV_WILLNEED)
                        list_del_init(&bo->base.madv_list);
-
-               mutex_unlock(&pfdev->shrinker_lock);
        }
+       mutex_unlock(&pfdev->shrinker_lock);
 
        drm_gem_object_put_unlocked(gem_obj);
        return 0;
-- 
2.23.0

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