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, 3 insertions, 3 deletions

diff --git a/drivers/gpu/nvgpu/gp106/clk_arb_gp106.c b/drivers/gpu/nvgpu/gp106/clk_arb_gp106.c
index ce0c03b9..2dd5651c 100644
--- a/drivers/gpu/nvgpu/gp106/clk_arb_gp106.c
+++ b/drivers/gpu/nvgpu/gp106/clk_arb_gp106.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"),
@@ -730,8 +730,8 @@ exit_arb:
                 nvgpu_atomic_set(&dev->poll_mask,
                  NVGPU_POLLIN | NVGPU_POLLRDNORM);
                 nvgpu_clk_arb_event_post_event(dev);
-                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(&arb->requests_lock);
 
@@ -768,4 +768,4 @@ void gp106_clk_arb_cleanup(struct nvgpu_clk_arb *arb)
         nvgpu_kfree(g, g->clk_arb);
 
         g->clk_arb = NULL;
-}
\ No newline at end of file
+}