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BUG: KCSAN: data-race in do_syslog / log_store

write to 0xffffffff89513200 of 8 bytes by task 14638 on cpu 1:
 log_store+0x7a2/0x7d0 kernel/printk/printk.c:672
 cont_flush kernel/printk/printk.c:1869 [inline]
 cont_add kernel/printk/printk.c:1898 [inline]
 log_output kernel/printk/printk.c:1914 [inline]
 vprintk_store+0x6cc/0x700 kernel/printk/printk.c:1983
 vprintk_emit+0x114/0x4f0 kernel/printk/printk.c:2011
 vprintk_default+0x24/0x30 kernel/printk/printk.c:2047
 vprintk_func+0x13d/0x140 kernel/printk/printk_safe.c:393
 printk+0x62/0x82 kernel/printk/printk.c:2078
 log_ctrl drivers/media/v4l2-core/v4l2-ctrls.c:3022 [inline]
 v4l2_ctrl_handler_log_status+0x263/0x2a0 drivers/media/v4l2-core/v4l2-ctrls.c:3043
 v4l2_ctrl_log_status+0x92/0xb0 drivers/media/v4l2-core/v4l2-ctrls.c:4591
 vidioc_log_status+0x48/0xc0 drivers/media/test-drivers/vivid/vivid-core.c:417
 v4l_log_status+0x5a/0xc0 drivers/media/v4l2-core/v4l2-ioctl.c:2502
 __video_do_ioctl+0x65b/0x870 drivers/media/v4l2-core/v4l2-ioctl.c:2990
 video_usercopy+0x6d8/0xfe0 drivers/media/v4l2-core/v4l2-ioctl.c:3306
 video_ioctl2+0x25/0x30 drivers/media/v4l2-core/v4l2-ioctl.c:3343
 v4l2_ioctl+0xc2/0xd0 drivers/media/v4l2-core/v4l2-dev.c:360
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffffff89513200 of 8 bytes by task 8284 on cpu 0:
 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:607
 __do_sys_read fs/read_write.c:617 [inline]
 __se_sys_read fs/read_write.c:615 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:615
 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: 8284 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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