This was been fixed in 4.20.x  upstream:


commit c393e9b2d51540b74e18e555df14706098dbf2cc
Author: Randy Dunlap <rdunlap@infradead.org>
Date:   Mon Nov 13 18:08:48 2017 +0200

   drm/amdkfd: fix amdkfd use-after-free GP fault

   Fix GP fault caused by dev_info() reference to a struct device*
   after the device has been freed (use after free).
   kfd_chardev_exit() frees the device so 'kfd_device' should not
   be used after calling kfd_chardev_exit().

   Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
   Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_module.c
b/drivers/gpu/drm/amd/amdkfd/kfd_module.c
index 6c5a9ca..f744cae 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_module.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_module.c
@@ -24,6 +24,7 @@
#include <linux/sched.h>
#include <linux/moduleparam.h>
#include <linux/device.h>
+#include <linux/printk.h>
#include "kfd_priv.h"

#define KFD_DRIVER_AUTHOR      "AMD Inc. and others"
@@ -132,7 +133,7 @@ static void __exit kfd_module_exit(void)
       kfd_process_destroy_wq();
       kfd_topology_shutdown();
       kfd_chardev_exit();
-       dev_info(kfd_device, "Removed module\n");
+       pr_info("amdkfd: Removed module\n");
}




[root@jpd-vmbase02 ~]# modprobe  amdkfd
[  132.453287] AMD IOMMUv2 driver by Joerg Roedel <jroedel@suse.de>
[  132.454004] AMD IOMMUv2 functionality not available on this system
[  132.507733] CRAT table not found
[  132.508139] Finished initializing topology ret=0
[  132.508802] kfd kfd: Initialized module
[root@jpd-vmbase02 ~]# modprobe  -r amdkfd
[  137.447829] amdkfd: Removed module
[root@jpd-vmbase02 ~]#
[root@jpd-vmbase02 ~]#