==================================================================
BUG: KCSAN: data-race in do_syslog / log_store

write to 0xffffffff8950f200 of 8 bytes by task 3853 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
 disk_unlock_native_capacity block/partitions/core.c:619 [inline]
 blk_add_partition block/partitions/core.c:661 [inline]
 blk_add_partitions+0x992/0xc60 block/partitions/core.c:758
 bdev_disk_changed+0x270/0x320 fs/block_dev.c:1416
 loop_reread_partitions drivers/block/loop.c:658 [inline]
 loop_set_status+0x750/0x7d0 drivers/block/loop.c:1427
 lo_ioctl+0x757/0x1190 drivers/block/loop.c:1495
 __blkdev_driver_ioctl block/ioctl.c:224 [inline]
 blkdev_ioctl+0x1cf/0x410 block/ioctl.c:620
 block_ioctl+0x6d/0x80 fs/block_dev.c:1871
 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 0xffffffff8950f200 of 8 bytes by task 8368 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: 8368 Comm: in:imklog Not tainted 5.9.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================