syzbot

loop4: detected capacity change from 0 to 1024
EXT4-fs: Ignoring removed nobh option
EXT4-fs: Ignoring removed bh option
==================================================================
BUG: KCSAN: data-race in data_push_tail / string

write to 0xffffffff88e42230 of 1 bytes by task 17063 on cpu 0:
 string_nocheck lib/vsprintf.c:643 [inline]
 string+0x187/0x220 lib/vsprintf.c:721
 vsnprintf+0x532/0x890 lib/vsprintf.c:2874
 vscnprintf+0x41/0x90 lib/vsprintf.c:2939
 printk_sprint+0x30/0x2d0 kernel/printk/printk.c:2216
 vprintk_store+0x599/0x860 kernel/printk/printk.c:2336
 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:1345
 fat_fill_super+0x15bf/0x1ce0 fs/fat/inode.c:1814
 vfat_fill_super+0x24/0x30 fs/fat/namei_vfat.c:1197
 get_tree_bdev_flags+0x28e/0x300 fs/super.c:1681
 get_tree_bdev+0x1f/0x30 fs/super.c:1704
 vfat_get_tree+0x1c/0x30 fs/fat/namei_vfat.c:1202
 vfs_get_tree+0x57/0x1d0 fs/super.c:1804
 do_new_mount+0x207/0x680 fs/namespace.c:3885
 path_mount+0x4a4/0xb20 fs/namespace.c:4209
 do_mount fs/namespace.c:4222 [inline]
 __do_sys_mount fs/namespace.c:4433 [inline]
 __se_sys_mount+0x28f/0x2e0 fs/namespace.c:4410
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4410
 x64_sys_call+0xd36/0x2fb0 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

read to 0xffffffff88e42230 of 8 bytes by task 17073 on cpu 1:
 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
 __ext4_msg+0x135/0x1a0 fs/ext4/super.c:983
 ext4_parse_param+0x7c1/0xf10 fs/ext4/super.c:2173
 vfs_parse_fs_param+0x142/0x2a0 fs/fs_context.c:146
 vfs_parse_fs_string fs/fs_context.c:188 [inline]
 vfs_parse_monolithic_sep+0x18a/0x200 fs/fs_context.c:230
 generic_parse_monolithic+0x24/0x30 fs/fs_context.c:258
 parse_monolithic_mount_data+0x43/0x60 fs/fs_context.c:723
 do_new_mount+0x1da/0x680 fs/namespace.c:3881
 path_mount+0x4a4/0xb20 fs/namespace.c:4209
 do_mount fs/namespace.c:4222 [inline]
 __do_sys_mount fs/namespace.c:4433 [inline]
 __se_sys_mount+0x28f/0x2e0 fs/namespace.c:4410
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4410
 x64_sys_call+0xd36/0x2fb0 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: 0x00000000ffffe4c1 -> 0x282073662d544146

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 17073 Comm: syz.4.6057 Not tainted 6.16.0-rc2-syzkaller-00269-g11313e2f7812 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================
EXT4-fs warning (device loop4): ext4_multi_mount_protect:398: Unable to create kmmpd thread for loop4.