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BUG: KCSAN: data-race in _prb_read_valid / prb_reserve

write to 0xffffffff86ac1c10 of 8 bytes by task 1918 on cpu 0:
 prb_reserve+0x769/0xbb0 kernel/printk/printk_ringbuffer.c:1538
 vprintk_store+0x3e9/0x9b0 kernel/printk/printk.c:2005
 vprintk_emit+0xca/0x360 kernel/printk/printk.c:2057
 vprintk_default+0x22/0x30 kernel/printk/printk.c:2091
 vprintk_func+0x11b/0x120 kernel/printk/printk_safe.c:393
 printk+0x62/0x82 kernel/printk/printk.c:2122
 __nla_validate_parse+0x1404/0x1730 lib/nlattr.c:600
 __nla_parse+0x3c/0x50 lib/nlattr.c:685
 nla_parse_nested_deprecated include/net/netlink.h:1231 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3292 [inline]
 rtnl_newlink+0x30d/0x12f0 net/core/rtnetlink.c:3491
 rtnetlink_rcv_msg+0x723/0x7c0 net/core/rtnetlink.c:5553
 netlink_rcv_skb+0x13e/0x240 net/netlink/af_netlink.c:2494
 rtnetlink_rcv+0x18/0x20 net/core/rtnetlink.c:5571
 netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
 netlink_unicast+0x5df/0x6b0 net/netlink/af_netlink.c:1330
 netlink_sendmsg+0x6f8/0x7c0 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg net/socket.c:672 [inline]
 ____sys_sendmsg+0x352/0x4c0 net/socket.c:2345
 ___sys_sendmsg net/socket.c:2399 [inline]
 __sys_sendmsg+0x1ed/0x270 net/socket.c:2432
 __do_sys_sendmsg net/socket.c:2441 [inline]
 __se_sys_sendmsg net/socket.c:2439 [inline]
 __x64_sys_sendmsg+0x42/0x50 net/socket.c:2439
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffffff86ac1c10 of 8 bytes by task 4877 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:480 [inline]
 prb_first_seq kernel/printk/printk_ringbuffer.c:1835 [inline]
 _prb_read_valid+0x763/0x8f0 kernel/printk/printk_ringbuffer.c:1881
 prb_first_valid_seq+0x32/0x70 kernel/printk/printk_ringbuffer.c:1985
 devkmsg_poll+0xd9/0x120 kernel/printk/printk.c:825
 vfs_poll include/linux/poll.h:90 [inline]
 ep_item_poll fs/eventpoll.c:840 [inline]
 ep_send_events fs/eventpoll.c:1677 [inline]
 ep_poll fs/eventpoll.c:1792 [inline]
 do_epoll_wait+0x6ad/0xf00 fs/eventpoll.c:2220
 __do_sys_epoll_wait fs/eventpoll.c:2232 [inline]
 __se_sys_epoll_wait fs/eventpoll.c:2227 [inline]
 __x64_sys_epoll_wait+0xf6/0x120 fs/eventpoll.c:2227
 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: 4877 Comm: systemd-journal Not tainted 5.11.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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