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BUG: KCSAN: data-race in data_alloc / prb_reserve

write to 0xffffffff86c758d8 of 8 bytes by task 26795 on cpu 0:
 data_alloc+0x31c/0x390 kernel/printk/printk_ringbuffer.c:1130
 prb_reserve+0x8d7/0xae0 kernel/printk/printk_ringbuffer.c:1724
 vprintk_store+0x54a/0x910 kernel/printk/printk.c:2354
 vprintk_emit+0x1a4/0x600 kernel/printk/printk.c:2455
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2494
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2504
 __netdev_printk+0x310/0x370 net/core/dev.c:12992
 netdev_info+0xa6/0xd0 net/core/dev.c:13039
 __dev_set_promiscuity+0x1fb/0x3f0 net/core/dev.c:9622
 netif_set_promiscuity+0x39/0x90 net/core/dev.c:9657
 dev_set_promiscuity+0xc1/0x170 net/core/dev_api.c:287
 hsr_portdev_setup net/hsr/hsr_slave.c:155 [inline]
 hsr_add_port+0x3bc/0x600 net/hsr/hsr_slave.c:213
 hsr_dev_finalize+0x4f4/0x6d0 net/hsr/hsr_device.c:794
 hsr_newlink+0x5ba/0x650 net/hsr/hsr_netlink.c:128
 rtnl_newlink_create+0x1e4/0x650 net/core/rtnetlink.c:3862
 __rtnl_newlink net/core/rtnetlink.c:3993 [inline]
 rtnl_newlink+0x1185/0x1400 net/core/rtnetlink.c:4108
 rtnetlink_rcv_msg+0x64b/0x720 net/core/rtnetlink.c:6994
 netlink_rcv_skb+0x123/0x220 net/netlink/af_netlink.c:2550
 rtnetlink_rcv+0x1c/0x30 net/core/rtnetlink.c:7021
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x5a8/0x680 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x5c8/0x6f0 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec net/socket.c:787 [inline]
 __sock_sendmsg net/socket.c:802 [inline]
 __sys_sendto+0x42e/0x490 net/socket.c:2265
 __do_sys_sendto net/socket.c:2272 [inline]
 __se_sys_sendto net/socket.c:2268 [inline]
 __x64_sys_sendto+0x76/0x90 net/socket.c:2268
 x64_sys_call+0x2d35/0x3020 arch/x86/include/generated/asm/syscalls_64.h:45
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86c758d8 of 8 bytes by task 26884 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:496 [inline]
 desc_push_tail kernel/printk/printk_ringbuffer.c:792 [inline]
 desc_reserve kernel/printk/printk_ringbuffer.c:938 [inline]
 prb_reserve+0x207/0xae0 kernel/printk/printk_ringbuffer.c:1674
 vprintk_store+0x54a/0x910 kernel/printk/printk.c:2354
 vprintk_emit+0x1a4/0x600 kernel/printk/printk.c:2455
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2494
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2504
 caif_disconnect_client+0x13d/0x150 net/caif/cfcnfg.c:194
 caif_release+0xec/0x250 net/caif/caif_socket.c:918
 __sock_release net/socket.c:722 [inline]
 sock_close+0x6b/0x150 net/socket.c:1514
 __fput+0x29b/0x630 fs/file_table.c:510
 ____fput+0x1c/0x30 fs/file_table.c:538
 task_work_run+0x130/0x1a0 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
 exit_to_user_mode_loop+0x1f4/0x6f0 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:328 [inline]
 do_syscall_64+0x232/0x3b0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000000aee00 -> 0x000000000015c618

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 26884 Comm: syz.2.5528 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
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