loop2: detected capacity change from 0 to 256
FAT-fs (loop2): Directory bread(block 64) failed
FAT-fs (loop2): Directory bread(block 65) failed
==================================================================
BUG: KCSAN: data-race in data_alloc / data_push_tail

write to 0xffffffff88e4d870 of 8 bytes by task 27471 on cpu 1:
 data_alloc+0x203/0x2b0 kernel/printk/printk_ringbuffer.c:1082
 prb_reserve+0x808/0xaf0 kernel/printk/printk_ringbuffer.c:1669
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2326
 vprintk_emit+0x178/0x650 kernel/printk/printk.c:2426
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2465
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2475
 __netdev_printk+0x321/0x3e0 net/core/dev.c:12588
 netdev_err+0x9b/0xd0 net/core/dev.c:12632
 netif_change_tx_queue_len+0x154/0x170 net/core/dev.c:9719
 dev_change_tx_queue_len+0xc0/0x170 net/core/dev_api.c:157
 dev_ifsioc+0x1a1/0xaa0 net/core/dev_ioctl.c:623
 dev_ioctl+0x70a/0x960 net/core/dev_ioctl.c:824
 sock_do_ioctl+0x197/0x220 net/socket.c:1252
 sock_ioctl+0x41b/0x610 net/socket.c:1359
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:598 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:584
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:584
 x64_sys_call+0x1816/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff88e4d870 of 8 bytes by task 27464 on cpu 0:
 data_make_reusable kernel/printk/printk_ringbuffer.c:594 [inline]
 data_push_tail+0xfd/0x420 kernel/printk/printk_ringbuffer.c:679
 data_alloc+0xbf/0x2b0 kernel/printk/printk_ringbuffer.c:1054
 prb_reserve+0x808/0xaf0 kernel/printk/printk_ringbuffer.c:1669
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2326
 vprintk_emit+0x178/0x650 kernel/printk/printk.c:2426
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2465
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2475
 _fat_msg+0xa4/0xd0 fs/fat/misc.c:62
 fat__get_entry fs/fat/dir.c:102 [inline]
 fat_get_entry+0x52b/0x5d0 fs/fat/dir.c:128
 fat_get_short_entry fs/fat/dir.c:885 [inline]
 fat_subdirs+0xf6/0x190 fs/fat/dir.c:951
 fat_read_root+0x316/0x360 fs/fat/inode.c:1347
 fat_fill_super+0x15bf/0x1ce0 fs/fat/inode.c:1816
 vfat_fill_super+0x24/0x30 fs/fat/namei_vfat.c:1197
 get_tree_bdev_flags+0x291/0x300 fs/super.c:1692
 get_tree_bdev+0x1f/0x30 fs/super.c:1715
 vfat_get_tree+0x1c/0x30 fs/fat/namei_vfat.c:1202
 vfs_get_tree+0x54/0x1d0 fs/super.c:1815
 do_new_mount+0x207/0x5e0 fs/namespace.c:3805
 path_mount+0x4a4/0xb20 fs/namespace.c:4120
 do_mount fs/namespace.c:4133 [inline]
 __do_sys_mount fs/namespace.c:4344 [inline]
 __se_sys_mount+0x28f/0x2e0 fs/namespace.c:4321
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4321
 x64_sys_call+0x2b4d/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000001000028ec -> 0x00000001000036f5

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 27464 Comm: syz.2.7483 Not tainted 6.16.0-syzkaller-12245-g2988dfed8a5d #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
==================================================================
FAT-fs (loop2): Directory bread(block 66) failed
FAT-fs (loop2): Directory bread(block 67) failed
FAT-fs (loop2): Directory bread(block 68) failed
FAT-fs (loop2): Directory bread(block 69) failed
FAT-fs (loop2): Directory bread(block 70) failed
FAT-fs (loop2): Directory bread(block 71) failed
FAT-fs (loop2): Directory bread(block 72) failed
FAT-fs (loop2): Directory bread(block 73) failed