gpu: nvgpu: add support for refcount tracking

If enabled, track actions (gets and puts) on channel reference counters.
Dump the most recent actions to syslog when
gk20a_wait_until_counter_is_N gets stuck when closing a channel.
GK20A_CHANNEL_REFCOUNT_TRACKING specifies the size of the action
history. Default is to disable completely, as this has some runtime
overhead.

Bug 1826754

Change-Id: I880b0efe8881044d02ae224c243a51cb6c2db8c1
Signed-off-by: Konsta Holtta <kholtta@nvidia.com>
Reviewed-on: http://git-master/r/1262424
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

1 files changed, 47 insertions, 1 deletions

diff --git a/drivers/gpu/nvgpu/gk20a/channel_gk20a.h b/drivers/gpu/nvgpu/gk20a/channel_gk20a.h
index 697d1603..44a989da 100644
--- a/drivers/gpu/nvgpu/gk20a/channel_gk20a.h
+++ b/drivers/gpu/nvgpu/gk20a/channel_gk20a.h
@@ -1,7 +1,7 @@
 /*
  * GK20A graphics channel
  *
- * Copyright (c) 2011-2016, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2011-2017, NVIDIA CORPORATION.  All rights reserved.
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms and conditions of the GNU General Public License,
@@ -24,6 +24,7 @@
 #include <linux/semaphore.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
+#include <linux/stacktrace.h>
 #include <linux/wait.h>
 #include <uapi/linux/nvgpu.h>
 
@@ -115,6 +116,40 @@ struct channel_gk20a_clean_up {
         struct delayed_work wq;
 };
 
+/*
+ * Track refcount actions, saving their stack traces. This number specifies how
+ * many most recent actions are stored in a buffer. Set to 0 to disable. 128
+ * should be enough to track moderately hard problems from the start.
+ */
+#define GK20A_CHANNEL_REFCOUNT_TRACKING 0
+/* Stack depth for the saved actions. */
+#define GK20A_CHANNEL_REFCOUNT_TRACKING_STACKLEN 8
+
+/*
+ * Because the puts and gets are not linked together explicitly (although they
+ * should always come in pairs), it's not possible to tell which ref holder to
+ * delete from the list when doing a put. So, just store some number of most
+ * recent gets and puts in a ring buffer, to obtain a history.
+ *
+ * These are zeroed when a channel is closed, so a new one starts fresh.
+ */
+
+enum channel_gk20a_ref_action_type {
+        channel_gk20a_ref_action_get,
+        channel_gk20a_ref_action_put
+};
+
+struct channel_gk20a_ref_action {
+        enum channel_gk20a_ref_action_type type;
+        unsigned long jiffies;
+        /*
+         * Many of these traces will be similar. Simpler to just capture
+         * duplicates than to have a separate database for the entries.
+         */
+        struct stack_trace trace;
+        unsigned long trace_entries[GK20A_CHANNEL_REFCOUNT_TRACKING_STACKLEN];
+};
+
 /* this is the priv element of struct nvhost_channel */
 struct channel_gk20a {
         struct gk20a *g; /* set only when channel is active */
@@ -125,6 +160,17 @@ struct channel_gk20a {
         bool referenceable;
         atomic_t ref_count;
         wait_queue_head_t ref_count_dec_wq;
+#if GK20A_CHANNEL_REFCOUNT_TRACKING
+        /*
+         * Ring buffer for most recent refcount gets and puts. Protected by
+         * ref_actions_lock when getting or putting refs (i.e., adding
+         * entries), and when reading entries.
+         */
+        struct channel_gk20a_ref_action ref_actions[
+                GK20A_CHANNEL_REFCOUNT_TRACKING];
+        size_t ref_actions_put; /* index of next write */
+        spinlock_t ref_actions_lock;
+#endif
 
         struct gk20a_semaphore_int *hw_sema;