gpu: nvgpu: fix clk_arb completion file private data access race

clk_arb completion file descriptor can get closed immediately after
poll finishes in the work item gp10b_clk_arb_run_arbiter_cb. In
that case, the refcount for nvgpu_clk_dev can become zero in
the work item and can lead to invalid access while removing
nvgpu_clk_dev from the lists.

Remove nvgpu_clk_dev from the list before dropping the reference to
it.

Also, delete the nvgpu_clk_dev in completion file release handler
within the session and requests spinlocks to avoid race with
gp10b_clk_arb_run_arbiter_cb using it.

bug 200757277

Change-Id: I054eee547f2a6fa633d7ef55df216ec36647a826
Signed-off-by: Sagar Kamble <skamble@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvgpu/+/2569522
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>
Reviewed-by: Debarshi Dutta <ddutta@nvidia.com>
Reviewed-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-by: Bibek Basu <bbasu@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/gpu/nvgpu/clk/clk_arb.c b/drivers/gpu/nvgpu/clk/clk_arb.c
index 6cf005c8..8e9fb419 100644
--- a/drivers/gpu/nvgpu/clk/clk_arb.c
+++ b/drivers/gpu/nvgpu/clk/clk_arb.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2018, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2016-2021, 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"),
@@ -886,8 +886,8 @@ void nvgpu_clk_arb_free_session(struct nvgpu_ref *refcount)
         nvgpu_spinlock_acquire(&session->session_lock);
         nvgpu_list_for_each_entry_safe(dev, tmp, &session->targets,
                         nvgpu_clk_dev, node) {
-                nvgpu_ref_put(&dev->refcount, nvgpu_clk_arb_free_fd);
                 nvgpu_list_del(&dev->node);
+                nvgpu_ref_put(&dev->refcount, nvgpu_clk_arb_free_fd);
         }
         nvgpu_spinlock_release(&session->session_lock);