drm/amdgpu: Fix sigsev when accessing MMIO on hot unplug.

Protect with drm_dev_enter/exit
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c

@@ -23,6 +23,7 @@
  */
 
 #include <drm/drm_auth.h>
+#include <drm/drm_drv.h>
 #include "amdgpu.h"
 #include "amdgpu_sched.h"
 #include "amdgpu_ras.h"
@@ -339,7 +340,7 @@ static void amdgpu_ctx_fini(struct kref *ref)
 {
 	struct amdgpu_ctx *ctx = container_of(ref, struct amdgpu_ctx, refcount);
 	struct amdgpu_device *adev = ctx->adev;
-	unsigned i, j;
+	unsigned i, j, idx;
 
 	if (!adev)
 		return;
@@ -350,7 +351,12 @@ static void amdgpu_ctx_fini(struct kref *ref)
 			ctx->entities[i][j] = NULL;
 		}
 	}
-	amdgpu_ctx_set_stable_pstate(ctx, AMDGPU_CTX_STABLE_PSTATE_NONE);
+
+	if (drm_dev_enter(&adev->ddev, &idx)) {
+		amdgpu_ctx_set_stable_pstate(ctx, AMDGPU_CTX_STABLE_PSTATE_NONE);
+		drm_dev_exit(idx);
+	}
+
 	kfree(ctx);
 }