[PATCH net v4 2/2] bonding: fix u32 overflow in compute_gap()
From: Hangbin Liu
Date: Thu Aug 20 2026 - 01:57:23 EST
From: Hangbin Liu <liuhangbin@xxxxxxxxxx>
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 u64 arithmetic throughout. Return 0 when the
speed is unknown or the slave is already overloaded.
Detected by AI code review.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Hangbin Liu <liuhangbin@xxxxxxxxxx>
---
drivers/net/bonding/bond_alb.c | 65 ++++++++++++++++++++++++++++++------------
include/net/bond_alb.h | 11 +++----
2 files changed, 53 insertions(+), 23 deletions(-)
diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
index 0afed2c39231..372db54803d3 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;
@@ -168,27 +169,38 @@ static void tlb_deinitialize(struct bonding *bond)
spin_unlock_bh(&bond->mode_lock);
}
-static long long compute_gap(struct slave *slave)
+static u64 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 */
+ u64 slave_load = SLAVE_TLB_INFO(slave).load << 3; /* Bytes to bits */
+ u32 raw_speed = READ_ONCE(slave->speed);
+ u64 speed = (u64)raw_speed << 20; /* Convert to bits per sec */
+
+ /* It's meaningless to compare gap on unknown speed NIC */
+ if (raw_speed == (u32)SPEED_UNKNOWN)
+ return 0;
+
+ /* Skip slave which is over loaded */
+ if (speed <= slave_load)
+ return 0;
+
+ return speed - slave_load;
}
static struct slave *tlb_get_least_loaded_slave(struct bonding *bond)
{
struct slave *slave, *least_loaded;
struct list_head *iter;
- long long max_gap;
+ u64 max_gap = 0;
least_loaded = NULL;
- max_gap = LLONG_MIN;
/* Find the slave with the largest gap */
bond_for_each_slave_rcu(bond, slave, iter) {
if (bond_slave_can_tx(slave)) {
- long long gap = compute_gap(slave);
+ u64 gap = compute_gap(slave);
- if (max_gap < gap) {
+ /* Make sure we have one available slave */
+ if (max_gap <= gap) {
least_loaded = slave;
max_gap = gap;
}
@@ -1354,8 +1366,14 @@ static netdev_tx_t bond_do_alb_xmit(struct sk_buff *skb, struct bonding *bond,
if (!tx_slave) {
/* unbalanced or unassigned, send through primary */
tx_slave = rcu_dereference(bond->curr_active_slave);
- if (bond->params.tlb_dynamic_lb)
- this_cpu_add(bond_info->unbalanced_load->tx_bytes, skb->len);
+ if (bond->params.tlb_dynamic_lb) {
+ struct unbalanced_load_stats *pcpu_load;
+
+ pcpu_load = this_cpu_ptr(bond_info->unbalanced_load);
+ u64_stats_update_begin(&pcpu_load->syncp);
+ u64_stats_add(&pcpu_load->tx_bytes, skb->len);
+ u64_stats_update_end(&pcpu_load->syncp);
+ }
}
if (tx_slave && bond_slave_can_tx(tx_slave)) {
@@ -1539,21 +1557,27 @@ netdev_tx_t bond_alb_xmit(struct sk_buff *skb, struct net_device *bond_dev)
return bond_do_alb_xmit(skb, bond, tx_slave);
}
-static u32 reset_unbalanced_load(struct alb_bond_info *bond_info)
+static u64 reset_unbalanced_load(struct alb_bond_info *bond_info)
{
+ u64 delta, tx_bytes, total_bytes = 0;
struct unbalanced_load_stats *p;
- u32 delta, total_bytes = 0;
+ unsigned int start;
int i;
for_each_possible_cpu(i) {
p = per_cpu_ptr(bond_info->unbalanced_load, i);
- total_bytes += READ_ONCE(p->tx_bytes);
+ do {
+ start = u64_stats_fetch_begin(&p->syncp);
+ tx_bytes = u64_stats_read(&p->tx_bytes);
+ } while (u64_stats_fetch_retry(&p->syncp, start));
+
+ total_bytes += tx_bytes;
}
delta = total_bytes - bond_info->prev_total_unbalanced;
bond_info->prev_total_unbalanced = total_bytes;
- return delta / BOND_TLB_REBALANCE_INTERVAL;
+ return div_u64(delta, BOND_TLB_REBALANCE_INTERVAL);
}
void bond_alb_monitor(struct work_struct *work)
@@ -1597,8 +1621,13 @@ void bond_alb_monitor(struct work_struct *work)
if (atomic_read(&bond_info->tx_rebalance_counter) >= BOND_TLB_REBALANCE_TICKS) {
bond_for_each_slave_rcu(bond, slave, iter) {
tlb_clear_slave(bond, slave, 1);
- if (slave == rcu_access_pointer(bond->curr_active_slave))
- SLAVE_TLB_INFO(slave).load = reset_unbalanced_load(bond_info);
+ if (slave == rcu_access_pointer(bond->curr_active_slave)) {
+ u64 new_load = reset_unbalanced_load(bond_info);
+
+ spin_lock_bh(&bond->mode_lock);
+ SLAVE_TLB_INFO(slave).load = new_load;
+ spin_unlock_bh(&bond->mode_lock);
+ }
}
atomic_set(&bond_info->tx_rebalance_counter, 0);
}
diff --git a/include/net/bond_alb.h b/include/net/bond_alb.h
index 6fb09b4fc7e2..32f1981033e4 100644
--- a/include/net/bond_alb.h
+++ b/include/net/bond_alb.h
@@ -57,12 +57,12 @@ struct tlb_client_info {
* packets to a Client that the Hash function
* gave this entry index.
*/
- u32 tx_bytes; /* Each Client accumulates the BytesTx that
+ u64 tx_bytes; /* Each Client accumulates the BytesTx that
* were transmitted to it, and after each
* CallBack the LoadHistory is divided
* by the balance interval
*/
- u32 load_history; /* This field contains the amount of Bytes
+ u64 load_history; /* This field contains the amount of Bytes
* that were transmitted to this client by
* the server on the previous balance
* interval in Bps.
@@ -118,19 +118,20 @@ struct tlb_slave_info {
* are the entries that were assigned to use this
* slave for transmit.
*/
- u32 load; /* Each slave sums the loadHistory of all clients
+ u64 load; /* Each slave sums the loadHistory of all clients
* assigned to it
*/
};
struct unbalanced_load_stats {
- u32 tx_bytes;
+ u64_stats_t tx_bytes;
+ struct u64_stats_sync syncp;
};
struct alb_bond_info {
struct tlb_client_info *tx_hashtbl; /* Dynamically allocated */
struct unbalanced_load_stats __percpu *unbalanced_load;
- u32 prev_total_unbalanced;
+ u64 prev_total_unbalanced;
atomic_t tx_rebalance_counter;
int lp_counter;
/* -------- rlb parameters -------- */
--
2.55.0