[PATCH net v3 0/2] bonding: fix TLB load-tracking overflow on high-speed NICs

[Hangbin Liu]

The bonding TLB (Transmit Load Balancing) mode tracks per-slave and
per-client transmit byte counts in u32 fields. At sustained throughput
above ~3.2 Gbit/s over the 10-second rebalance interval these counters
wrap, causing compute_gap() to produce incorrect gap values and
mis-select transmit slaves. Such speeds are routine on modern NICs
under heavy traffic.

This two-patch series fixes the overflow by widening the relevant
fields to u64.

Patch 1 converts the unbalanced_load counter to per-cpu state as a
preparatory step. The counter sits in the transmit hot path, so
converting it to per-cpu before widening avoids introducing cross-CPU
synchronization overhead for a u64.

Patch 2 widens tx_bytes, load_history, load, and the per-cpu
unbalanced_load tx_bytes from u32 to u64. It adds u64_stats_sync
protection for the per-cpu counter to prevent tearing on 32-bit
architectures, and reworks compute_gap() to use u64 arithmetic with
READ_ONCE() on slave->speed.

Note: In patch 2, I return 0 directly when the speed is unknown, because
I believe the comparison becomes meaningless if the NIC speed cannot be
determined. For example: a 1 G NIC and a 10 G NIC are bonded together,
yet both are marked as unknown. If you would prefer to retain the existing
logic, we could instead set the speed to `ULLONG_MAX` when speed is unknown.

Signed-off-by: Hangbin Liu <liuhangbin@xxxxxxxxxx>
---
Changes in v3:
- Add a preparatory patch to convert unbalanced_load to per-cpu first
- widens tlb counters to u64 and add helpers to prevent tearing on 32-bit
- Link to v2: https://lore.kernel.org/r/20260814-bond_overflow-v2-1-d3fe588ad167@xxxxxxxxxx

Changes in v2:
- update comment description, including AI-detected info.
- fix tx_bytes/load type detected by sashiko
- cast SPEED_UNKNOWN to 0 before shift, detected by sashiko
- Link to v1: https://lore.kernel.org/r/20260810-bond_overflow-v1-1-c9ff29d76770@xxxxxxxxxx

---
Hangbin Liu (2):
      bonding: convert unbalanced_load to per-cpu state
      bonding: fix u32 overflow in compute_gap()

 drivers/net/bonding/bond_alb.c  | 69 +++++++++++++++++++++++++++++++----------
 drivers/net/bonding/bond_main.c |  9 ++++++
 include/net/bond_alb.h          | 13 +++++---
 3 files changed, 71 insertions(+), 20 deletions(-)
---
base-commit: 21040c7f931502070dcc66bb0f1aeed07dec032b
change-id: 20260806-bond_overflow-ac6a6a78d6a0

Best regards,
-- 
Hangbin Liu <liuhangbin@xxxxxxxxxx>