netdev: fix repeated netlink messages in queue stats

[ Upstream commit ecc391a541 ]

The context is supposed to record the next queue to dump,
not last dumped. If the dump doesn't fit we will restart
from the already-dumped queue, duplicating the message.

Before this fix and with the selftest improvements later
in this series we see:

  # ./run_kselftest.sh -t drivers/net:stats.py
  timeout set to 45
  selftests: drivers/net: stats.py
  KTAP version 1
  1..5
  ok 1 stats.check_pause
  ok 2 stats.check_fec
  ok 3 stats.pkt_byte_sum
  # Check| At /root/ksft-net-drv/drivers/net/./stats.py, line 125, in qstat_by_ifindex:
  # Check|     ksft_eq(len(queues[qtype]), len(set(queues[qtype])),
  # Check failed 45 != 44 repeated queue keys
  # Check| At /root/ksft-net-drv/drivers/net/./stats.py, line 127, in qstat_by_ifindex:
  # Check|     ksft_eq(len(queues[qtype]), max(queues[qtype]) + 1,
  # Check failed 45 != 44 missing queue keys
  # Check| At /root/ksft-net-drv/drivers/net/./stats.py, line 125, in qstat_by_ifindex:
  # Check|     ksft_eq(len(queues[qtype]), len(set(queues[qtype])),
  # Check failed 45 != 44 repeated queue keys
  # Check| At /root/ksft-net-drv/drivers/net/./stats.py, line 127, in qstat_by_ifindex:
  # Check|     ksft_eq(len(queues[qtype]), max(queues[qtype]) + 1,
  # Check failed 45 != 44 missing queue keys
  # Check| At /root/ksft-net-drv/drivers/net/./stats.py, line 125, in qstat_by_ifindex:
  # Check|     ksft_eq(len(queues[qtype]), len(set(queues[qtype])),
  # Check failed 103 != 100 repeated queue keys
  # Check| At /root/ksft-net-drv/drivers/net/./stats.py, line 127, in qstat_by_ifindex:
  # Check|     ksft_eq(len(queues[qtype]), max(queues[qtype]) + 1,
  # Check failed 103 != 100 missing queue keys
  # Check| At /root/ksft-net-drv/drivers/net/./stats.py, line 125, in qstat_by_ifindex:
  # Check|     ksft_eq(len(queues[qtype]), len(set(queues[qtype])),
  # Check failed 102 != 100 repeated queue keys
  # Check| At /root/ksft-net-drv/drivers/net/./stats.py, line 127, in qstat_by_ifindex:
  # Check|     ksft_eq(len(queues[qtype]), max(queues[qtype]) + 1,
  # Check failed 102 != 100 missing queue keys
  not ok 4 stats.qstat_by_ifindex
  ok 5 stats.check_down
  # Totals: pass:4 fail:1 xfail:0 xpass:0 skip:0 error:0

With the fix:

  # ./ksft-net-drv/run_kselftest.sh -t drivers/net:stats.py
  timeout set to 45
  selftests: drivers/net: stats.py
  KTAP version 1
  1..5
  ok 1 stats.check_pause
  ok 2 stats.check_fec
  ok 3 stats.pkt_byte_sum
  ok 4 stats.qstat_by_ifindex
  ok 5 stats.check_down
  # Totals: pass:5 fail:0 xfail:0 xpass:0 skip:0 error:0

Fixes: ab63a2387c ("netdev: add per-queue statistics")
Reviewed-by: Joe Damato <jdamato@fastly.com>
Link: https://patch.msgid.link/20241213152244.3080955-3-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

net/core/netdev-genl.c

@@ -597,7 +597,7 @@ netdev_nl_stats_by_queue(struct net_device *netdev, struct sk_buff *rsp,
 					    i, info);
 		if (err)
 			return err;
-		ctx->rxq_idx = i++;
+		ctx->rxq_idx = ++i;
 	}
 	i = ctx->txq_idx;
 	while (ops->get_queue_stats_tx && i < netdev->real_num_tx_queues) {
@@ -605,7 +605,7 @@ netdev_nl_stats_by_queue(struct net_device *netdev, struct sk_buff *rsp,
 					    i, info);
 		if (err)
 			return err;
-		ctx->txq_idx = i++;
+		ctx->txq_idx = ++i;
 	}
 
 	ctx->rxq_idx = 0;