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BUG: KCSAN: data-race in br_fdb_update / br_fdb_update

read to 0xffff888103a56b40 of 8 bytes by interrupt on cpu 0:
 br_fdb_update+0x106/0x460 net/bridge/br_fdb.c:903
 br_handle_frame_finish+0x31a/0xf50 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+0x4c6/0x570 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:283 [inline]
 br_handle_frame+0x4fa/0x9e0 net/bridge/br_input.c:434
 __netif_receive_skb_core+0xad3/0x23b0 net/core/dev.c:5878
 __netif_receive_skb_one_core net/core/dev.c:5989 [inline]
 __netif_receive_skb+0x59/0x270 net/core/dev.c:6104
 process_backlog+0x229/0x420 net/core/dev.c:6456
 __napi_poll+0x66/0x310 net/core/dev.c:7506
 napi_poll net/core/dev.c:7569 [inline]
 net_rx_action+0x391/0x830 net/core/dev.c:7696
 handle_softirqs+0xb7/0x290 kernel/softirq.c:579
 run_ksoftirqd+0x1c/0x30 kernel/softirq.c:968
 smpboot_thread_fn+0x32b/0x530 kernel/smpboot.c:160
 kthread+0x489/0x510 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 0xffff888103a56b40 of 8 bytes by interrupt on cpu 1:
 br_fdb_update+0x13e/0x460 net/bridge/br_fdb.c:904
 br_handle_frame_finish+0x31a/0xf50 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+0x4c6/0x570 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:283 [inline]
 br_handle_frame+0x4fa/0x9e0 net/bridge/br_input.c:434
 __netif_receive_skb_core+0xad3/0x23b0 net/core/dev.c:5878
 __netif_receive_skb_one_core net/core/dev.c:5989 [inline]
 __netif_receive_skb+0x59/0x270 net/core/dev.c:6104
 process_backlog+0x229/0x420 net/core/dev.c:6456
 __napi_poll+0x66/0x310 net/core/dev.c:7506
 napi_poll net/core/dev.c:7569 [inline]
 net_rx_action+0x391/0x830 net/core/dev.c:7696
 handle_softirqs+0xb7/0x290 kernel/softirq.c:579
 do_softirq+0x5d/0x90 kernel/softirq.c:480
 __local_bh_enable_ip+0x70/0x80 kernel/softirq.c:407
 __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]
 nsim_dev_trap_report drivers/net/netdevsim/dev.c:835 [inline]
 nsim_dev_trap_report_work+0x52b/0x630 drivers/net/netdevsim/dev.c:866
 process_one_work kernel/workqueue.c:3236 [inline]
 process_scheduled_works+0x4cb/0x9d0 kernel/workqueue.c:3319
 worker_thread+0x582/0x770 kernel/workqueue.c:3400
 kthread+0x489/0x510 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

value changed: 0x0000000100001113 -> 0x0000000100001114

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 5790 Comm: kworker/u8:38 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Workqueue: events_unbound nsim_dev_trap_report_work
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