tbv: data-credit leak reconciliation counters (localize 768-window stall)

The credit-return threshold fix is a no-op at the default window (768), so a
hang there is a slow leak (consumed-but-never-returned), not batch withholding.
Add two atomic64 counters per path and globally, exposed in debugfs:
  data_tx_credit_consumed  - every data frame charged a credit (TX charge site)
  data_rx_credit_eligible  - every received credit-consuming frame (RX)
Reconciliation: across a link, sender consumed == receiver eligible; locally,
eligible == credit_sent + rx_credit_pending. A persistent gap localizes the
leak (transit loss -> consumed > peer eligible; return-side drop -> eligible >
sent+pending). Read on 021/022 after a 16K ping-pong stall.

Author: doctorpangloss

drivers/thunderbolt_ibverbs/kernel/debugfs.c

@@ -193,6 +193,10 @@ static int tbv_debugfs_summary_show(struct seq_file *s, void *unused)
 		   atomic64_read(&state->data_tx_credit_stalls));
 	seq_printf(s, "data_tx_credit_received: %lld\n",
 		   atomic64_read(&state->data_tx_credit_received));
+	seq_printf(s, "data_tx_credit_consumed: %lld\n",
+		   atomic64_read(&state->data_tx_credit_consumed));
+	seq_printf(s, "data_rx_credit_eligible: %lld\n",
+		   atomic64_read(&state->data_rx_credit_eligible));
 	seq_printf(s, "data_rx_completed: %lld\n",
 		   atomic64_read(&state->data_rx_completed));
 	seq_printf(s, "data_rx_credit_sent: %lld\n",
@@ -400,12 +404,13 @@ static int tbv_debugfs_peers_show(struct seq_file *s, void *unused)
 				   rail->remote_tx_hop,
 				   rail->remote_rx_hop);
 			seq_printf(s,
-				   "    data_tx_enqueued=%lld data_tx_posted=%lld data_tx_completed=%lld data_tx_credit_stalls=%lld data_tx_credit_received=%lld tx_credits=%u/%u\n",
+				   "    data_tx_enqueued=%lld data_tx_posted=%lld data_tx_completed=%lld data_tx_credit_stalls=%lld data_tx_credit_received=%lld data_tx_credit_consumed=%lld tx_credits=%u/%u\n",
 				   atomic64_read(&rail->path.data_tx_enqueued),
 				   atomic64_read(&rail->path.data_tx_posted),
 				   atomic64_read(&rail->path.data_tx_completed),
 				   atomic64_read(&rail->path.data_tx_credit_stalls),
 				   atomic64_read(&rail->path.data_tx_credit_received),
+				   atomic64_read(&rail->path.data_tx_credit_consumed),
 				   rail->path.tx_remote_data_credits,
 				   rail->path.tx_remote_data_credit_max);
 			seq_printf(s,
@@ -425,9 +430,10 @@ static int tbv_debugfs_peers_show(struct seq_file *s, void *unused)
 				   rail->path.cfg.sof_mask,
 				   rail->path.cfg.eof_mask);
 				seq_printf(s,
-					   "    data_rx_completed=%lld data_rx_credit_sent=%lld data_rx_credit_send_error=%lld data_rx_repost_failed=%lld rx_credit_pending=%u\n",
+					   "    data_rx_completed=%lld data_rx_credit_sent=%lld data_rx_credit_eligible=%lld data_rx_credit_send_error=%lld data_rx_repost_failed=%lld rx_credit_pending=%u\n",
 					   atomic64_read(&rail->path.data_rx_completed),
 					   atomic64_read(&rail->path.data_rx_credit_sent),
+					   atomic64_read(&rail->path.data_rx_credit_eligible),
 					   atomic64_read(&rail->path.data_rx_credit_send_error),
 					   atomic64_read(&rail->path.data_rx_repost_failed),
 					   rail->path.rx_data_credit_pending);

drivers/thunderbolt_ibverbs/kernel/path.c

@@ -987,6 +987,12 @@ static void tbv_path_rx_complete(struct tb_ring *ring, struct ring_frame *frame,
 		atomic64_inc(&state->data_rx_bad_frame);
 	}
 
+	if (return_rx_credits) {
+		if (state)
+			atomic64_inc(&state->data_rx_credit_eligible);
+		atomic64_inc(&path->data_rx_credit_eligible);
+	}
+
 	if (path->state == TBV_PATH_RING_STARTED ||
 	    path->state == TBV_PATH_TUNNEL_ENABLED) {
 		int ret = tbv_path_post_rx_frame(f);
@@ -1864,6 +1870,9 @@ static void tbv_path_schedule_tx(struct tbv_path *path)
 			}
 			path->tx_remote_data_credits--;
 			charged_data_credit = true;
+			if (state)
+				atomic64_inc(&state->data_tx_credit_consumed);
+			atomic64_inc(&path->data_tx_credit_consumed);
 		}
 		packet->start_credit_group_frames = 0;
 

drivers/thunderbolt_ibverbs/kernel/tbv.h

@@ -218,6 +218,16 @@ struct tbv_path {
 	atomic64_t control_tx_queue_max_ms;
 	atomic64_t data_tx_credit_stalls;
 	atomic64_t data_tx_credit_received;
+	/*
+	 * Leak reconciliation for the software data-credit window. Across a link
+	 * the sender's consumed (every charged data frame) must equal the
+	 * receiver's eligible (every received credit-consuming frame); locally
+	 * the receiver's eligible must equal credit_sent + rx_data_credit_pending.
+	 * A persistent divergence localizes a credit leak (frames lost in transit
+	 * -> consumed > peer eligible; return-side drop -> eligible > sent+pending).
+	 */
+	atomic64_t data_tx_credit_consumed;
+	atomic64_t data_rx_credit_eligible;
 	atomic64_t data_rx_completed;
 	atomic64_t data_rx_credit_sent;
 	atomic64_t data_rx_credit_send_error;
@@ -578,6 +588,16 @@ struct tbv_state {
 	atomic64_t data_tx_errors;
 	atomic64_t data_tx_credit_stalls;
 	atomic64_t data_tx_credit_received;
+	/*
+	 * Leak reconciliation for the software data-credit window. Across a link
+	 * the sender's consumed (every charged data frame) must equal the
+	 * receiver's eligible (every received credit-consuming frame); locally
+	 * the receiver's eligible must equal credit_sent + rx_data_credit_pending.
+	 * A persistent divergence localizes a credit leak (frames lost in transit
+	 * -> consumed > peer eligible; return-side drop -> eligible > sent+pending).
+	 */
+	atomic64_t data_tx_credit_consumed;
+	atomic64_t data_rx_credit_eligible;
 	atomic64_t data_rx_completed;
 	atomic64_t data_rx_credit_sent;
 	atomic64_t data_rx_credit_send_error;