On 7/14/26 5:59 AM, Simon Horman wrote:

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---
ibmveth: Add per-queue RX and TX statistics collection and reporting

This commit introduces per-queue statistics tracking for both receive and
transmit paths in the ibmveth driver. The counters are aggregated for legacy
interfaces and exposed individually via ethtool stringsets.

quoted

diff --git a/drivers/net/ethernet/ibm/ibmveth.c b/drivers/net/ethernet/ibm/ibmveth.c
index 863e5c68b42c7..4e3f49b6346fd 100644
--- a/drivers/net/ethernet/ibm/ibmveth.c
+++ b/drivers/net/ethernet/ibm/ibmveth.c

[ ... ]

quoted

@@ -1655,6 +1655,10 @@ static int ibmveth_open(struct net_device *netdev)
  	if (rc)
  		goto out_cleanup_rx_interrupts;
  
+	rc = ibmveth_alloc_tx_qstats(adapter);
+	if (rc)
+		goto out_free_tx_resources;
+
  	netif_tx_start_all_queues(netdev);
  
  	netdev_dbg(netdev, "open complete\n");

[ ... ]

quoted

  out_cleanup_rx_interrupts:
  	ibmveth_cleanup_rx_interrupts(adapter);
  out_free_tx_resources:
  	ibmveth_free_tx_resources(adapter);

[Severity: High]
Does the goto out_free_tx_resources on ibmveth_alloc_tx_qstats() failure
bypass the cleanup for RX interrupts?

Since out_free_tx_resources is physically below out_cleanup_rx_interrupts in
ibmveth_open(), failing here leaves the IRQs requested and NAPI enabled. If
an interrupt subsequently fires, could the handler access the freed RX queue
memory and cause a kernel panic?

[ ... ]

*

  Confirmed — that goto skips RX interrupt cleanup. Will fix the

  open() unwind order in v4 so TX-stat allocation failure still

  disables NAPI and frees IRQs before tearing down queues.

*

quoted

@@ -1699,6 +1699,7 @@ static int ibmveth_close(struct net_device *netdev)
  		}
  	}
  
+	ibmveth_free_tx_qstats(adapter);
  	ibmveth_free_tx_resources(adapter);
  	ibmveth_cleanup_rx_interrupts(adapter);
  	ibmveth_update_rx_no_buffer(adapter);

[ ... ]

quoted

  	ibmveth_free_rx_qstats(adapter);

[Severity: High]
If ibmveth_close() is called to bring down the interface, does this
unconditionally free adapter->tx_qstats and adapter->rx_qstats without a
grace period?

Confirmed.

Since ibmveth_get_stats64() can be called concurrently under RCU, and
ibmveth_start_xmit() can run concurrently if the datapath is not completely
synchronized, could this lead to a use-after-free or NULL pointer dereference
when these functions access the freed arrays?

[ ... ]

*

  Good point. ndo_get_stats64 can run without RTNL. In v4 I’ll give

  the qstat arrays adapter lifetime (probe/remove) instead of

  open/close, so close cannot free them under concurrent readers.

*

quoted

@@ -1967,22 +1967,107 @@ static int ibmveth_set_features(struct net_device *dev,

[ ... ]

quoted

+static void ibmveth_aggregate_rx_qstats(struct ibmveth_adapter *adapter)
+{
+	u64 total_invalid = 0;
+	u64 total_large = 0;
+	int i;
+
+	if (!adapter->rx_qstats)
+		return;
+
+	for (i = 0; i < adapter->num_rx_queues; i++) {
+		total_invalid += adapter->rx_qstats[i].invalid_buffers;
+		total_large += adapter->rx_qstats[i].large_packets;
+	}
+
+	adapter->rx_invalid_buffer = total_invalid;
+	adapter->rx_large_packets = total_large;
+}

[Severity: High]
Does overwriting adapter->rx_invalid_buffer and other persistent global
counters with the dynamically allocated adapter->rx_qstats values cause a
permanent loss of interface statistics?

yes

When the interface is brought down and back up, ibmveth_close() frees the
queue stats arrays and ibmveth_open() reallocates them as zeroed. Will this
cause all historical statistics to be wiped out on every interface reset,
breaking standard persistence behavior?

[ ... ]

*

  Agreed this regresses persistence vs pre-MQ.

**

In v4 per-queue qstats will stay for the adapter lifetime, and adapter-level

ethtool strings are summed on read (ibmvnic-style). No dual-updating

globals on the hot path, and no aggregate_* that wipes history on reopen.

*

quoted

+static void ibmveth_get_strings(struct net_device *dev, u32 stringset, u8 *data)
+{

[ ... ]

quoted

+	for (i = 0; i < adapter->num_rx_queues; i++) {
+		ethtool_sprintf(&p, "rx%d_packets", i);
+		ethtool_sprintf(&p, "rx%d_bytes", i);

[Severity: Low]
Are these private ethtool stringsets duplicating standard kernel statistics?

According to the subsystem guidelines, per-queue packet and byte statistics
that have a standard UAPI representation (like struct netdev_queue_stats_rx
exported via netlink) should not be duplicated as private ethtool strings.

*

  Thanks — **

*I can move those to standard*

*

netdev queue stats and drop the ethtool duplicates in a follow-up. For

now I'll keep device-specific counters (interrupts, polls, invalid, …)

as private ethtool strings.

*


*

quoted

diff --git a/drivers/net/ethernet/ibm/ibmveth.h b/drivers/net/ethernet/ibm/ibmveth.h
index f7b20fd01acb5..390c660af979e 100644
--- a/drivers/net/ethernet/ibm/ibmveth.h
+++ b/drivers/net/ethernet/ibm/ibmveth.h

@@ -316,9 +316,21 @@ struct ibmveth_rx_queue_stats {
  	u64 no_buffer_drops;
  };
  
+struct ibmveth_tx_queue_stats {
+	u64 packets;
+	u64 bytes;
+	u64 large_packets;
+	u64 dropped_packets;
+	u64 send_failures;
+	u64 checksum_offload;
+};

[Severity: Medium]
Will this structure layout prevent cache line false sharing?

The commit message mentions tracking transmit counters per TX queue to avoid
cache line contention, but struct ibmveth_tx_queue_stats appears to be
exactly 48 bytes and lacks cacheline alignment annotations like
____cacheline_aligned. When allocated as a contiguous array, will multiple
CPUs processing different queues end up writing to the same hardware
cacheline?

*Will add cacheline alignment for the per-queue stats structs in v4*

*Thanks again for your valuable feedback!*

*Mingming*