==================================================================
BUG: KCSAN: data-race in data_alloc / prb_reserve

write to 0xffffffff8606a968 of 8 bytes by task 19345 on cpu 0:
 data_alloc+0x291/0x2c0 kernel/printk/printk_ringbuffer.c:1096
 prb_reserve+0x85e/0xb60 kernel/printk/printk_ringbuffer.c:1669
 vprintk_store+0x53f/0x810 kernel/printk/printk.c:2266
 vprintk_emit+0x10c/0x5e0 kernel/printk/printk.c:2326
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2360
 vprintk+0x75/0x80 kernel/printk/printk_safe.c:45
 _printk+0x7a/0xa0 kernel/printk/printk.c:2370
 set_capacity_and_notify+0xff/0x160 block/genhd.c:86
 loop_set_size+0x2e/0x70 drivers/block/loop.c:235
 loop_configure+0xae8/0xc80 drivers/block/loop.c:1121
 lo_ioctl+0x682/0x1330
 blkdev_ioctl+0x35f/0x450 block/ioctl.c:676
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xd3/0x150 fs/ioctl.c:893
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:893
 x64_sys_call+0x1581/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff8606a968 of 8 bytes by task 19347 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:482 [inline]
 desc_push_tail kernel/printk/printk_ringbuffer.c:778 [inline]
 desc_reserve kernel/printk/printk_ringbuffer.c:924 [inline]
 prb_reserve+0x235/0xb60 kernel/printk/printk_ringbuffer.c:1619
 vprintk_store+0x53f/0x810 kernel/printk/printk.c:2266
 vprintk_emit+0x10c/0x5e0 kernel/printk/printk.c:2326
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2360
 vprintk+0x75/0x80 kernel/printk/printk_safe.c:45
 _printk+0x7a/0xa0 kernel/printk/printk.c:2370
 __ip6_tnl_rcv+0x936/0x950 net/ipv6/ip6_tunnel.c:860
 ip6_tnl_rcv+0x64/0x80 net/ipv6/ip6_tunnel.c:900
 gre_rcv+0x81d/0x950
 ip6_protocol_deliver_rcu+0xae6/0x1050 net/ipv6/ip6_input.c:438
 ip6_input_finish net/ipv6/ip6_input.c:483 [inline]
 NF_HOOK include/linux/netfilter.h:314 [inline]
 ip6_input+0xbd/0x1b0 net/ipv6/ip6_input.c:492
 ip6_mc_input+0x34a/0x480 net/ipv6/ip6_input.c:586
 dst_input include/net/dst.h:460 [inline]
 ip6_rcv_finish+0x320/0x330 net/ipv6/ip6_input.c:79
 NF_HOOK include/linux/netfilter.h:314 [inline]
 ipv6_rcv+0x74/0x150 net/ipv6/ip6_input.c:310
 __netif_receive_skb_one_core net/core/dev.c:5625 [inline]
 __netif_receive_skb+0xa2/0x280 net/core/dev.c:5739