EXT4-fs error (device loop3): ext4_mb_generate_buddy:1315: group 0, 
==================================================================
BUG: KCSAN: data-race in data_push_tail / string

write to 0xffffffff8936a0e0 of 1 bytes by task 28 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+0x30/0x2c0 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
 kauditd_printk_skb kernel/audit.c:587 [inline]
 kauditd_hold_skb+0x1b1/0x1c0 kernel/audit.c:622
 kauditd_send_queue+0x273/0x2c0 kernel/audit.c:807
 kauditd_thread+0x444/0x670 kernel/audit.c:931
 kthread+0x22a/0x280 kernel/kthread.c:467
 ret_from_fork+0x150/0x360 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffffff8936a0e0 of 8 bytes by task 16237 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_realloc kernel/printk/printk_ringbuffer.c:1193 [inline]
 prb_reserve_in_last+0x892/0xb30 kernel/printk/printk_ringbuffer.c:1495
 vprintk_store+0x457/0x910 kernel/printk/printk.c:2328
 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
 __ext4_grp_locked_error+0x5db/0x7c0 fs/ext4/super.c:1068
 ext4_mb_generate_buddy+0x3a0/0x430 fs/ext4/mballoc.c:1312
 ext4_mb_init_cache+0x887/0xbf0 fs/ext4/mballoc.c:1497
 ext4_mb_init_group+0x42d/0x580 fs/ext4/mballoc.c:1655
 ext4_mb_good_group_nolock fs/ext4/mballoc.c:2827 [inline]
 ext4_mb_scan_group+0x5f4/0xf20 fs/ext4/mballoc.c:2964
 ext4_mb_scan_groups_linear fs/ext4/mballoc.c:1176 [inline]
 ext4_mb_scan_groups fs/ext4/mballoc.c:1206 [inline]
 ext4_mb_regular_allocator+0x67f/0x16b0 fs/ext4/mballoc.c:3056
 ext4_mb_new_blocks+0x7db/0x1f00 fs/ext4/mballoc.c:6318
 ext4_ext_map_blocks+0xdc3/0x2f50 fs/ext4/extents.c:4438
 ext4_map_create_blocks+0xce/0x3a0 fs/ext4/inode.c:616
 ext4_map_blocks+0x594/0x970 fs/ext4/inode.c:809
 ext4_getblk+0x128/0x530 fs/ext4/inode.c:977
 ext4_bread+0x28/0x110 fs/ext4/inode.c:1040
 ext4_quota_write+0x166/0x360 fs/ext4/super.c:7367
 write_blk fs/quota/quota_tree.c:70 [inline]
 find_free_dqentry+0x53e/0x690 fs/quota/quota_tree.c:318
 do_insert_tree+0x54e/0xad0 fs/quota/quota_tree.c:400
 do_insert_tree+0x767/0xad0 fs/quota/quota_tree.c:402
 do_insert_tree+0x767/0xad0 fs/quota/quota_tree.c:402
 do_insert_tree+0x749/0xad0 fs/quota/quota_tree.c:402
 dq_insert_tree fs/quota/quota_tree.c:432 [inline]
 qtree_write_dquot+0x2cb/0x300 fs/quota/quota_tree.c:451
 v2_write_dquot+0xd9/0x130 fs/quota/quota_v2.c:372
 dquot_acquire+0x1c2/0x2b0 fs/quota/dquot.c:473
 ext4_acquire_dquot+0x15f/0x200 fs/ext4/super.c:6999
 dqget+0x527/0x8c0 fs/quota/dquot.c:980
 __dquot_initialize+0x20c/0x7c0 fs/quota/dquot.c:1508
 dquot_initialize+0x1a/0x30 fs/quota/dquot.c:1570
 ext4_process_orphan+0x32/0x1c0 fs/ext4/orphan.c:327
 ext4_orphan_cleanup+0x6a8/0xa00 fs/ext4/orphan.c:472
 __ext4_fill_super fs/ext4/super.c:5670 [inline]
 ext4_fill_super+0x3408/0x37c0 fs/ext4/super.c:5793
 get_tree_bdev_flags+0x291/0x300 fs/super.c:1694
 get_tree_bdev+0x1f/0x30 fs/super.c:1717
 ext4_get_tree+0x1c/0x30 fs/ext4/super.c:5825
 vfs_get_tree+0x57/0x1d0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]
 do_new_mount_fc fs/namespace.c:3760 [inline]
 do_new_mount+0x288/0x8d0 fs/namespace.c:3836
 path_mount+0x4d0/0xbc0 fs/namespace.c:4146
 do_mount fs/namespace.c:4159 [inline]
 __do_sys_mount fs/namespace.c:4348 [inline]
 __se_sys_mount+0x28c/0x2e0 fs/namespace.c:4325
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4325
 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: 0x00000000fffff829 -> 0x207b20206465696e

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 16237 Comm: syz.3.3754 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
==================================================================
block bitmap and bg descriptor inconsistent: 48 vs 41 free clusters
EXT4-fs (loop3): Remounting filesystem read-only
EXT4-fs (loop3): 1 truncate cleaned up
EXT4-fs (loop3): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: writeback.
syz.3.3754 (16237) used greatest stack depth: 6976 bytes left