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

write to 0xffffffff89395d70 of 1 bytes by task 7647 on cpu 1:
 string_nocheck lib/vsprintf.c:659 [inline]
 string+0x187/0x220 lib/vsprintf.c:737
 vsnprintf+0x532/0x860 lib/vsprintf.c:2948
 vscnprintf+0x41/0x90 lib/vsprintf.c:3013
 printk_sprint+0x30/0x2e0 kernel/printk/printk.c:2222
 vprintk_store+0x57b/0x910 kernel/printk/printk.c:2364
 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:12942
 netdev_info+0xa6/0xd0 net/core/dev.c:12989
 netif_set_allmulti+0x14c/0x220 net/core/dev.c:9643
 dev_set_allmulti+0xcc/0x170 net/core/dev_api.c:313
 nbp_delete_promisc net/bridge/br_if.c:252 [inline]
 del_nbp+0x67/0x720 net/bridge/br_if.c:340
 br_dev_delete+0x4e/0xe0 net/bridge/br_if.c:386
 br_del_bridge+0x97/0xc0 net/bridge/br_if.c:496
 br_ioctl_stub+0x58f/0x8f0 net/bridge/br_ioctl.c:-1
 br_ioctl_call net/socket.c:1227 [inline]
 sock_ioctl+0x39c/0x610 net/socket.c:1329
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
 x64_sys_call+0x1563/0x3020 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff89395d70 of 8 bytes by task 7656 on cpu 0:
 data_make_reusable kernel/printk/printk_ringbuffer.c:608 [inline]
 data_push_tail+0x100/0x470 kernel/printk/printk_ringbuffer.c:693
 data_alloc+0x11b/0x390 kernel/printk/printk_ringbuffer.c:1089
 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
 mnt_warn_timestamp_expiry+0x1c3/0x200 fs/namespace.c:3305
 do_new_mount_fc fs/namespace.c:3779 [inline]
 do_new_mount+0x354/0x8d0 fs/namespace.c:3839
 path_mount+0x4d0/0xbc0 fs/namespace.c:4159
 do_mount fs/namespace.c:4172 [inline]
 __do_sys_mount fs/namespace.c:4361 [inline]
 __se_sys_mount+0x28c/0x2e0 fs/namespace.c:4338
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4338
 x64_sys_call+0x2d61/0x3020 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000ffffe402 -> 0x735f656764697262

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 7656 Comm: syz.9.767 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================
EXT4-fs error (device loop9): htree_dirblock_to_tree:1080: inode #2: block 4: comm syz.9.767: bad entry in directory: directory entry overrun - offset=1012, inode=128, rec_len=65544, size=1024 fake=0
EXT4-fs (loop9): Remounting filesystem read-only