gpu: nvgpu: Fix PMU destroy sequence

A call to exit the PMU state machine/kthread must
be prioritized over any other state change.
It was possible to set the state as PMU_STATE_EXIT,
signal the kthread and overwrite the state before
the kthread has had the chance to exit its loop.
This may lead to a "lost" signal, resulting in
indefinite wait during the destroy sequence.

Faulting sequence:
1. pmu_state = PMU_STATE_EXIT in nvgpu_pmu_destroy()
2. cond_signal()
3. pmu_state = PMU_STATE_LOADING_PG_BUF
4. PMU kthread wakes up
5. PMU kthread processes PMU_STATE_LOADING_PG_BUF
6. PMU kthread sleeps
7. nvgpu_pmu_destroy() waits indefinitely

This patch adds a sticky flag to indicate PMU_STATE_EXIT,
irrespective of any subsequent changes to pmu_state.

The PMU PG init kthread may wait on a call to
NVGPU_COND_WAIT_INTERRUPTIBLE, which requires a
corresponding call to nvgpu_cond_signal_interruptible()
as the core kernel code requires this task mask to
wake-up an interruptible task.

Bug 2658750
Bug 200532122

Change-Id: I61beae80673486f83bf60c703a8af88b066a1c36
Signed-off-by: Abhiroop Kaginalkar <akaginalkar@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/2177112
(cherry picked from commit afa49fb073a324c49a820e142aaaf80e4656dcc6)
Reviewed-on: https://git-master.nvidia.com/r/2190733
Tested-by: Divya Singhatwaria <dsinghatwari@nvidia.com>
Reviewed-by: Debarshi Dutta <ddutta@nvidia.com>
Reviewed-by: Alex Waterman <alexw@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Bibek Basu <bbasu@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/gpu/nvgpu/include/nvgpu/pmu.h b/drivers/gpu/nvgpu/include/nvgpu/pmu.h
index 00194ec0..dcd49481 100644
--- a/drivers/gpu/nvgpu/include/nvgpu/pmu.h
+++ b/drivers/gpu/nvgpu/include/nvgpu/pmu.h
@@ -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"),
@@ -301,6 +301,7 @@ struct pmu_sequence {
 
 struct nvgpu_pg_init {
         bool state_change;
+        bool state_destroy;
         struct nvgpu_cond wq;
         struct nvgpu_thread state_task;
 };