amdgpu: a NULL ->mm does not mean a thread is a kthread

Use the proper API instead.

Fixes: 70539bd7 ("drm/amd: Update MEC HQD loading code for KFD")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Cc: Felipe Balbi <balbi@kernel.org>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: http://lkml.kernel.org/r/20200404094101.672954-1-hch@lst.de
Link: http://lkml.kernel.org/r/20200404094101.672954-2-hch@lst.deSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h

@@ -196,7 +196,7 @@ uint8_t amdgpu_amdkfd_get_xgmi_hops_count(struct kgd_dev *dst, struct kgd_dev *s
 			pagefault_disable();				\
 			if ((mmptr) == current->mm) {			\
 				valid = !get_user((dst), (wptr));	\
-			} else if (current->mm == NULL) {		\
+			} else if (current->flags & PF_KTHREAD) {	\
 				kthread_use_mm(mmptr);			\
 				valid = !get_user((dst), (wptr));	\
 				kthread_unuse_mm(mmptr);		\