==================================================================
BUG: KCSAN: data-race in data_push_tail / vsnprintf

write to 0xffffffff870b98bf of 1 bytes by task 28308 on cpu 1:
 vsnprintf+0xdd0/0xe20
 va_format lib/vsprintf.c:1683 [inline]
 pointer+0x8a1/0xd10 lib/vsprintf.c:2455
 vsnprintf+0x861/0xe20 lib/vsprintf.c:2828
 vscnprintf+0x42/0x80 lib/vsprintf.c:2930
 printk_sprint+0x30/0x2d0 kernel/printk/printk.c:2124
 vprintk_store+0x56f/0x800 kernel/printk/printk.c:2238
 vprintk_emit+0xd0/0x5d0 kernel/printk/printk.c:2284
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2318
 vprintk+0x71/0x80 kernel/printk/printk_safe.c:45
 _printk+0x7a/0xa0 kernel/printk/printk.c:2328
 __ext4_msg+0x18a/0x1a0 fs/ext4/super.c:1006
 ext4_group_desc_init+0x13e0/0x1400 fs/ext4/super.c:4892
 __ext4_fill_super fs/ext4/super.c:5305 [inline]
 ext4_fill_super+0x23c6/0x39a0 fs/ext4/super.c:5703
 get_tree_bdev+0x250/0x2d0 fs/super.c:1619
 ext4_get_tree+0x1c/0x20 fs/ext4/super.c:5735
 vfs_get_tree+0x51/0x1b0 fs/super.c:1784
 do_new_mount+0x227/0x690 fs/namespace.c:3352
 path_mount+0x496/0xb30 fs/namespace.c:3679
 do_mount fs/namespace.c:3692 [inline]
 __do_sys_mount fs/namespace.c:3898 [inline]
 __se_sys_mount+0x27f/0x2d0 fs/namespace.c:3875
 __x64_sys_mount+0x67/0x80 fs/namespace.c:3875
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x59/0x120 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffffffff870b98b8 of 8 bytes by task 28320 on cpu 0:
 data_make_reusable kernel/printk/printk_ringbuffer.c:590 [inline]
 data_push_tail+0x102/0x430 kernel/printk/printk_ringbuffer.c:675
 data_alloc+0xbe/0x2c0 kernel/printk/printk_ringbuffer.c:1046
 prb_reserve+0x893/0xbc0 kernel/printk/printk_ringbuffer.c:1555
 vprintk_store+0x53e/0x800 kernel/printk/printk.c:2228
 vprintk_emit+0xd0/0x5d0 kernel/printk/printk.c:2284
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2318
 vprintk+0x71/0x80 kernel/printk/printk_safe.c:45
 _printk+0x7a/0xa0 kernel/printk/printk.c:2328
 caif_disconnect_client+0x133/0x140 net/caif/cfcnfg.c:194
 chnl_net_open+0x4ff/0x5a0 net/caif/chnl_net.c:327
 __dev_open+0x281/0x3a0 net/core/dev.c:1446
 __dev_change_flags+0x153/0x400 net/core/dev.c:8648
 dev_change_flags+0x59/0xd0 net/core/dev.c:8720
 do_setlink+0x839/0x2440 net/core/rtnetlink.c:2903
 rtnl_setlink+0x255/0x300 net/core/rtnetlink.c:3206
 rtnetlink_rcv_msg+0x80a/0x8c0 net/core/rtnetlink.c:6615
 netlink_rcv_skb+0x126/0x220 net/netlink/af_netlink.c:2543
 rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:6633
 netlink_unicast_kernel net/netlink/af_netlink.c:1341 [inline]
 netlink_unicast+0x589/0x650 net/netlink/af_netlink.c:1367
 netlink_sendmsg+0x66e/0x770 net/netlink/af_netlink.c:1908
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg net/socket.c:745 [inline]
 sock_write_iter+0x1aa/0x230 net/socket.c:1160
 do_iter_readv_writev+0x2b0/0x330
 vfs_writev+0x2e9/0x860 fs/read_write.c:971
 do_writev+0xf8/0x220 fs/read_write.c:1018
 __do_sys_writev fs/read_write.c:1091 [inline]
 __se_sys_writev fs/read_write.c:1088 [inline]
 __x64_sys_writev+0x45/0x50 fs/read_write.c:1088
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x59/0x120 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0x000000010000107c -> 0x0a21642164657470

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 28320 Comm: syz-executor.1 Not tainted 6.8.0-rc1-syzkaller-00026-g7ed2632ec7d7 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
==================================================================
syz-executor.1 (28320) used greatest stack depth: 8320 bytes left