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BUG: KCSAN: data-race in br_fdb_update / br_fdb_update

read to 0xffff88811a5b4a40 of 8 bytes by interrupt on cpu 1:
 br_fdb_update+0x106/0x460 net/bridge/br_fdb.c:1005
 br_handle_frame_finish+0x34b/0x1040 net/bridge/br_input.c:144
 br_nf_hook_thresh net/bridge/br_netfilter_hooks.c:-1 [inline]
 br_nf_pre_routing_finish+0x867/0xb90 net/bridge/br_netfilter_hooks.c:425
 rcu_read_unlock include/linux/rcupdate.h:873 [inline]
 nf_hook include/linux/netfilter.h:275 [inline]
 NF_HOOK+0x1be/0x200 include/linux/netfilter.h:316
 br_nf_pre_routing+0xad8/0xbd0 net/bridge/br_netfilter_hooks.c:534
 nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
 nf_hook_bridge_pre net/bridge/br_input.c:291 [inline]
 br_handle_frame+0x4fa/0x9e0 net/bridge/br_input.c:442
 __netif_receive_skb_core+0xad3/0x2550 net/core/dev.c:5966
 __netif_receive_skb_one_core net/core/dev.c:6077 [inline]
 __netif_receive_skb+0x59/0x270 net/core/dev.c:6192
 process_backlog+0x229/0x420 net/core/dev.c:6544
 __napi_poll+0x66/0x310 net/core/dev.c:7594
 napi_poll net/core/dev.c:7657 [inline]
 net_rx_action+0x423/0x8c0 net/core/dev.c:7784
 handle_softirqs+0xb7/0x290 kernel/softirq.c:622
 do_softirq+0x5d/0x90 kernel/softirq.c:523
 __local_bh_enable_ip+0x70/0x80 kernel/softirq.c:450
 __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:167 [inline]
 _raw_spin_unlock_bh+0x36/0x40 kernel/locking/spinlock.c:210
 spin_unlock_bh include/linux/spinlock.h:396 [inline]
 batadv_tt_local_purge+0x1a8/0x1f0 net/batman-adv/translation-table.c:1315
 batadv_tt_purge+0x2b/0x610 net/batman-adv/translation-table.c:3509
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0x4cb/0x9d0 kernel/workqueue.c:3346
 worker_thread+0x582/0x770 kernel/workqueue.c:3427
 kthread+0x486/0x510 kernel/kthread.c:463
 ret_from_fork+0x11f/0x1b0 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

write to 0xffff88811a5b4a40 of 8 bytes by interrupt on cpu 0:
 br_fdb_update+0x13e/0x460 net/bridge/br_fdb.c:1006
 br_handle_frame_finish+0x34b/0x1040 net/bridge/br_input.c:144
 br_nf_hook_thresh+0x1e8/0x220 net/bridge/br_netfilter_hooks.c:-1
 br_nf_pre_routing_finish_ipv6+0x4d1/0x570 net/bridge/br_netfilter_ipv6.c:-1
 NF_HOOK include/linux/netfilter.h:318 [inline]
 br_nf_pre_routing_ipv6+0x1fa/0x2b0 net/bridge/br_netfilter_ipv6.c:184
 br_nf_pre_routing+0x52b/0xbd0 net/bridge/br_netfilter_hooks.c:508
 nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
 nf_hook_bridge_pre net/bridge/br_input.c:291 [inline]
 br_handle_frame+0x4fa/0x9e0 net/bridge/br_input.c:442
 __netif_receive_skb_core+0xad3/0x2550 net/core/dev.c:5966
 __netif_receive_skb_one_core net/core/dev.c:6077 [inline]
 __netif_receive_skb+0x59/0x270 net/core/dev.c:6192
 process_backlog+0x229/0x420 net/core/dev.c:6544
 __napi_poll+0x66/0x310 net/core/dev.c:7594
 napi_poll net/core/dev.c:7657 [inline]
 net_rx_action+0x423/0x8c0 net/core/dev.c:7784
 handle_softirqs+0xb7/0x290 kernel/softirq.c:622
 do_softirq+0x5d/0x90 kernel/softirq.c:523
 __local_bh_enable_ip+0x70/0x80 kernel/softirq.c:450
 __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:167 [inline]
 _raw_spin_unlock_bh+0x36/0x40 kernel/locking/spinlock.c:210
 spin_unlock_bh include/linux/spinlock.h:396 [inline]
 lock_sock_nested+0x112/0x140 net/core/sock.c:3727
 lock_sock include/net/sock.h:1679 [inline]
 tcp_recvmsg+0x10e/0x480 net/ipv4/tcp.c:2924
 inet_recvmsg+0xb7/0x290 net/ipv4/af_inet.c:885
 sock_recvmsg_nosec net/socket.c:1078 [inline]
 sock_recvmsg+0xf6/0x170 net/socket.c:1100
 sock_read_iter+0x152/0x1a0 net/socket.c:1170
 new_sync_read fs/read_write.c:491 [inline]
 vfs_read+0x649/0x770 fs/read_write.c:572
 ksys_read+0xda/0x1a0 fs/read_write.c:715
 __do_sys_read fs/read_write.c:724 [inline]
 __se_sys_read fs/read_write.c:722 [inline]
 __x64_sys_read+0x40/0x50 fs/read_write.c:722
 x64_sys_call+0x27c0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:1
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x000000010000263c -> 0x000000010000263d

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3288 Comm: syz-executor Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
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