gpu: nvgpu: fix synchronization in nvgpu_vm_map

The mapping early returned from nvgpu_vm_map might already
be unmapped during channel clean up. Increase refcount of
an already mapped buffer inside the scope of update_gmmu_lock
mutex to avoid this race.

Bug 200494150

Change-Id: I66d9272e42c40cd3aae7ba3bb8106ec37691bf8e
Signed-off-by: Shih-hsin Li <seasonl@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/2114163
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-by: Alex Waterman <alexw@nvidia.com>
Reviewed-by: Vinayak Pane <vpane@nvidia.com>
Reviewed-by: Daniel Fu <danifu@nvidia.com>
Reviewed-by: svc-mobile-coverity <svc-mobile-coverity@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/gpu/nvgpu/common/mm/vm.c b/drivers/gpu/nvgpu/common/mm/vm.c
index 7f0b3d10..4e221500 100644
--- a/drivers/gpu/nvgpu/common/mm/vm.c
+++ b/drivers/gpu/nvgpu/common/mm/vm.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2018, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2017-2019, NVIDIA CORPORATION.  All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -873,12 +873,13 @@ struct nvgpu_mapped_buf *nvgpu_vm_map(struct vm_gk20a *vm,
                                                       map_addr,
                                                       flags,
                                                       map_key_kind);
-                nvgpu_mutex_release(&vm->update_gmmu_lock);
 
                 if (mapped_buffer) {
                         nvgpu_ref_get(&mapped_buffer->ref);
+                        nvgpu_mutex_release(&vm->update_gmmu_lock);
                         return mapped_buffer;
                 }
+                nvgpu_mutex_release(&vm->update_gmmu_lock);
         }
 
         /*