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BUG: KCSAN: data-race in do_syslog / log_store

write to 0xffffffff89513200 of 8 bytes by task 5 on cpu 0:
 log_store+0x7a2/0x7d0 kernel/printk/printk.c:672
 log_output kernel/printk/printk.c:1932 [inline]
 vprintk_store+0x5ba/0x700 kernel/printk/printk.c:1983
 vprintk_emit+0x114/0x4f0 kernel/printk/printk.c:2011
 dev_vprintk_emit+0x337/0x36f drivers/base/core.c:4129
 dev_printk_emit+0x6a/0x8c drivers/base/core.c:4140
 __dev_printk+0xfa/0x103 drivers/base/core.c:4152
 _dev_info+0x76/0x96 drivers/base/core.c:4198
 show_string drivers/usb/core/hub.c:2268 [inline]
 announce_device drivers/usb/core/hub.c:2285 [inline]
 usb_new_device+0x7cb/0xc60 drivers/usb/core/hub.c:2534
 hub_port_connect drivers/usb/core/hub.c:5208 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5348 [inline]
 port_event drivers/usb/core/hub.c:5494 [inline]
 hub_event+0x1d78/0x2bd0 drivers/usb/core/hub.c:5576
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffffffff89513200 of 8 bytes by task 8285 on cpu 1:
 do_syslog+0x344/0x1480 kernel/printk/printk.c:1561
 kmsg_read+0x7a/0xa0 fs/proc/kmsg.c:40
 pde_read fs/proc/inode.c:306 [inline]
 proc_reg_read+0xde/0x1a0 fs/proc/inode.c:316
 vfs_read+0x16d/0x5e0 fs/read_write.c:479
 ksys_read+0xce/0x180 fs/read_write.c:615
 __do_sys_read fs/read_write.c:625 [inline]
 __se_sys_read fs/read_write.c:623 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:623
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8285 Comm: in:imklog Not tainted 5.9.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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