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BUG: KCSAN: data-race in do_syslog / log_store

write to 0xffffffff86040010 of 8 bytes by task 9097 on cpu 1:
 log_store+0x2a9/0x430 kernel/printk/printk.c:660
 log_output kernel/printk/printk.c:1899 [inline]
 vprintk_store+0x297/0x430 kernel/printk/printk.c:1950
 vprintk_emit+0x146/0x4e0 kernel/printk/printk.c:1978
 vprintk_default+0x31/0x50 kernel/printk/printk.c:2023
 vprintk_func+0x85/0x140 kernel/printk/printk_safe.c:386
 printk+0x69/0x91 kernel/printk/printk.c:2056
 br_set_state net/bridge/br_stp.c:45 [inline]
 br_set_state.cold+0x7c/0xf5 net/bridge/br_stp.c:29
 br_make_forwarding+0xb9/0x190 net/bridge/br_stp.c:417
 br_port_state_selection+0x2cb/0x330 net/bridge/br_stp.c:449
 br_stp_enable_port+0x30/0x50 net/bridge/br_stp_if.c:94
 br_port_carrier_check+0x14f/0x250 net/bridge/br_if.c:80
 br_device_event+0x241/0x570 net/bridge/br.c:86
 notifier_call_chain+0xd7/0x160 kernel/notifier.c:95
 __raw_notifier_call_chain kernel/notifier.c:396 [inline]
 raw_notifier_call_chain+0x37/0x50 kernel/notifier.c:403

read to 0xffffffff86040010 of 8 bytes by task 7112 on cpu 0:
 do_syslog kernel/printk/printk.c:1525 [inline]
 do_syslog+0x12dc/0x13f0 kernel/printk/printk.c:1503
 kmsg_read+0x80/0xa0 fs/proc/kmsg.c:40
 proc_reg_read+0xe9/0x140 fs/proc/inode.c:223
 __vfs_read+0x67/0xc0 fs/read_write.c:425
 vfs_read fs/read_write.c:461 [inline]
 vfs_read+0x143/0x2c0 fs/read_write.c:446
 ksys_read+0xd5/0x1b0 fs/read_write.c:587
 __do_sys_read fs/read_write.c:597 [inline]
 __se_sys_read fs/read_write.c:595 [inline]
 __x64_sys_read+0x4c/0x60 fs/read_write.c:595
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7112 Comm: rsyslogd Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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