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BUG: KCSAN: data-race in _prb_read_valid / prb_reserve

write to 0xffffffff86b1a418 of 8 bytes by task 11630 on cpu 1:
 prb_reserve+0x769/0xbb0 kernel/printk/printk_ringbuffer.c:1541
 log_store kernel/printk/printk.c:506 [inline]
 log_output kernel/printk/printk.c:1935 [inline]
 vprintk_store+0x3c1/0x620 kernel/printk/printk.c:1986
 vprintk_emit+0xd6/0x370 kernel/printk/printk.c:2011
 dev_vprintk_emit+0x1c6/0x1ea drivers/base/core.c:4128
 dev_printk_emit+0x6a/0x8c drivers/base/core.c:4139
 __dev_printk+0xfa/0x103 drivers/base/core.c:4151
 _dev_warn+0x76/0x96 drivers/base/core.c:4195
 usb_parse_interface drivers/usb/core/config.c:593 [inline]
 usb_parse_configuration drivers/usb/core/config.c:795 [inline]
 usb_get_configuration+0x2519/0x29f0 drivers/usb/core/config.c:944
 usb_enumerate_device drivers/usb/core/hub.c:2387 [inline]
 usb_new_device+0xb3/0xc80 drivers/usb/core/hub.c:2523
 hub_port_connect drivers/usb/core/hub.c:5222 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5362 [inline]
 port_event drivers/usb/core/hub.c:5508 [inline]
 hub_event+0x1d25/0x2b60 drivers/usb/core/hub.c:5590
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2272
 worker_thread+0x635/0xb90 kernel/workqueue.c:2418
 kthread+0x1fa/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffffffff86b1a418 of 8 bytes by task 8017 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:480 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1756 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1804 [inline]
 _prb_read_valid+0x1c9/0x8f0 kernel/printk/printk_ringbuffer.c:1884
 prb_read_valid+0x39/0x60 kernel/printk/printk_ringbuffer.c:1933
 do_syslog+0x228/0x1400 kernel/printk/printk.c:1611
 kmsg_read+0x7a/0xa0 fs/proc/kmsg.c:40
 pde_read fs/proc/inode.c:321 [inline]
 proc_reg_read+0xe1/0x1b0 fs/proc/inode.c:331
 vfs_read+0x154/0x5c0 fs/read_write.c:494
 ksys_read+0xce/0x180 fs/read_write.c:634
 __do_sys_read fs/read_write.c:644 [inline]
 __se_sys_read fs/read_write.c:642 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:642
 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: 0 PID: 8017 Comm: in:imklog Not tainted 5.10.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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