Re: [PATCH net v5 2/2] bonding: fix u32 overflow in compute_gap()

[Paolo Abeni <pabeni@redhat.com>]

On 8/25/26 3:01 AM, Hangbin Liu wrote:
> From: Hangbin Liu <liuhangbin@kylinos.cn>
> 
> The TLB load-tracking fields tx_bytes, load_history, load, and
> unbalanced_load are all u32. At sustained throughput above ~3.2 Gbit/s
> over the 10-second rebalance interval the byte counters wrap, causing
> compute_gap() to produce incorrect gap values and mis-select slaves.
> Such speeds are common on modern NICs under heavy traffic.
> 
> Widen these fields to u64. Use u64_stats_sync to protect the per-cpu
> unbalanced_load_stats against tearing on 32-bit architectures, and
> div_u64() for the 64-bit divisions. The tx_bytes and load_history
> are protected in spin_lock. Also protect the slave load writing in
> bond_alb_monitor() with spin_lock in case of tear on 32-bit.
> 
> Rework compute_gap() to use s64 arithmetic throughout. Return LLONG_MIN
> when the speed is unknown.
> 
> Detected by AI code review.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Hangbin Liu <liuhangbin@kylinos.cn>
> ---
>  drivers/net/bonding/bond_alb.c | 52 ++++++++++++++++++++++++++++++------------
>  include/net/bond_alb.h         | 11 +++++----
>  2 files changed, 44 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
> index 0afed2c39231..9a43a1f47893 100644
> --- a/drivers/net/bonding/bond_alb.c
> +++ b/drivers/net/bonding/bond_alb.c
> @@ -6,6 +6,7 @@
>  #include <linux/skbuff.h>
>  #include <linux/netdevice.h>
>  #include <linux/etherdevice.h>
> +#include <linux/ethtool.h>
>  #include <linux/pkt_sched.h>
>  #include <linux/spinlock.h>
>  #include <linux/slab.h>
> @@ -74,8 +75,8 @@ static inline u8 _simple_hash(const u8 *hash_start, int hash_size)
>  static inline void tlb_init_table_entry(struct tlb_client_info *entry, int save_load)
>  {
>  	if (save_load) {
> -		entry->load_history = 1 + entry->tx_bytes /
> -				      BOND_TLB_REBALANCE_INTERVAL;
> +		entry->load_history = 1 + div_u64(entry->tx_bytes,
> +				      BOND_TLB_REBALANCE_INTERVAL);
>  		entry->tx_bytes = 0;
>  	}
>  
> @@ -133,7 +134,7 @@ static int tlb_initialize(struct bonding *bond)
>  	if (!new_hashtbl)
>  		return -ENOMEM;
>  
> -	bond_info->unbalanced_load = alloc_percpu(struct unbalanced_load_stats);
> +	bond_info->unbalanced_load = netdev_alloc_pcpu_stats(struct unbalanced_load_stats);
>  	if (!bond_info->unbalanced_load)
>  		goto out;
>  
> @@ -170,8 +171,14 @@ static void tlb_deinitialize(struct bonding *bond)
>  
>  static long long compute_gap(struct slave *slave)
>  {
> -	return (s64) (slave->speed << 20) - /* Convert to Megabit per sec */
> -	       (s64) (SLAVE_TLB_INFO(slave).load << 3); /* Bytes to bits */
> +	u32 raw_speed = READ_ONCE(slave->speed);
> +
> +	/* It's meaningless to compare gap on unknown speed NIC */
> +	if (raw_speed == (u32)SPEED_UNKNOWN)
> +		return LLONG_MIN;

Sashiko noted the above could entirely disable:

https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260825-bond_overflow-v5-0-7a800de133f1%40kylinos.cn

I think the v2 code for the above should be fine.

All other comments look noise to me.

/P