EXT4-fs (loop6): Total free blocks count 0
EXT4-fs (loop6): Free/Dirty block details
EXT4-fs (loop6): free_blocks=2415919104
EXT4-fs (loop6): dirty_blocks=8224
EXT4-fs (loop6): Block reservation details
EXT4-fs (loop6): i_reserved_data_blocks=514
==================================================================
BUG: KCSAN: data-race in data_alloc / data_push_tail

write to 0xffffffff88e6fc38 of 8 bytes by task 51 on cpu 0:
 data_alloc+0x215/0x2c0 kernel/printk/printk_ringbuffer.c:1082
 prb_reserve+0x86a/0xb80 kernel/printk/printk_ringbuffer.c:1669
 vprintk_store+0x552/0x860 kernel/printk/printk.c:2326
 vprintk_emit+0x1a0/0x6c0 kernel/printk/printk.c:2426
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2465
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x7f/0xb0 kernel/printk/printk.c:2475
 __ext4_grp_locked_error+0x5fa/0x810 fs/ext4/super.c:1058
 ext4_mb_generate_buddy+0x247/0x2d0 fs/ext4/mballoc.c:1217
 ext4_mb_init_cache+0x851/0xbd0 fs/ext4/mballoc.c:1406
 ext4_mb_init_group+0x245/0x3e0 fs/ext4/mballoc.c:1543
 ext4_mb_good_group_nolock fs/ext4/mballoc.c:2704 [inline]
 ext4_mb_regular_allocator+0xc3e/0x23f0 fs/ext4/mballoc.c:2903
 ext4_mb_new_blocks+0x81d/0x2020 fs/ext4/mballoc.c:6215
 ext4_ext_map_blocks+0x106c/0x36a0 fs/ext4/extents.c:4379
 ext4_map_create_blocks fs/ext4/inode.c:520 [inline]
 ext4_map_blocks+0x5c6/0xd00 fs/ext4/inode.c:706
 mpage_map_one_extent fs/ext4/inode.c:2224 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2277 [inline]
 ext4_do_writepages+0x14ef/0x21d0 fs/ext4/inode.c:2739
 ext4_writepages+0x183/0x320 fs/ext4/inode.c:2829
 do_writepages+0x1d8/0x480 mm/page-writeback.c:2656
 __writeback_single_inode+0x89/0x850 fs/fs-writeback.c:1680
 writeback_sb_inodes+0x458/0xa10 fs/fs-writeback.c:1976
 wb_writeback+0x264/0x650 fs/fs-writeback.c:2156
 wb_do_writeback fs/fs-writeback.c:2303 [inline]
 wb_workfn+0x1aa/0x960 fs/fs-writeback.c:2343
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0x4de/0xa20 kernel/workqueue.c:3319
 worker_thread+0x52c/0x710 kernel/workqueue.c:3400
 kthread+0x4b7/0x540 kernel/kthread.c:464
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffffff88e6fc38 of 8 bytes by task 110 on cpu 1:
 data_make_reusable kernel/printk/printk_ringbuffer.c:594 [inline]
 data_push_tail+0x107/0x440 kernel/printk/printk_ringbuffer.c:679
 data_alloc+0xbd/0x2c0 kernel/printk/printk_ringbuffer.c:1054
 prb_reserve+0x86a/0xb80 kernel/printk/printk_ringbuffer.c:1669
 vprintk_store+0x552/0x860 kernel/printk/printk.c:2326
 vprintk_emit+0x1a0/0x6c0 kernel/printk/printk.c:2426
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2465
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x7f/0xb0 kernel/printk/printk.c:2475
 __ext4_msg+0x198/0x1b0 fs/ext4/super.c:985
 ext4_print_free_blocks+0x17b/0x190 fs/ext4/inode.c:1641
 mpage_map_and_submit_extent fs/ext4/inode.c:2305 [inline]
 ext4_do_writepages+0x1a7f/0x21d0 fs/ext4/inode.c:2739
 ext4_writepages+0x183/0x320 fs/ext4/inode.c:2829
 do_writepages+0x1d8/0x480 mm/page-writeback.c:2656
 __writeback_single_inode+0x89/0x850 fs/fs-writeback.c:1680
 writeback_sb_inodes+0x458/0xa10 fs/fs-writeback.c:1976
 wb_writeback+0x264/0x650 fs/fs-writeback.c:2156
 wb_do_writeback fs/fs-writeback.c:2303 [inline]
 wb_workfn+0x1aa/0x960 fs/fs-writeback.c:2343
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0x4de/0xa20 kernel/workqueue.c:3319
 worker_thread+0x52c/0x710 kernel/workqueue.c:3400
 kthread+0x4b7/0x540 kernel/kthread.c:464
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x00000000ffffec85 -> 0x00000000fffff8ce

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 110 Comm: kworker/u8:4 Not tainted 6.15.0-rc2-syzkaller-00257-gb5c6891b2c5b #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Workqueue: writeback wb_workfn (flush-7:6)
==================================================================
EXT4-fs (loop6): Delayed block allocation failed for inode 15 at logical offset 18 with max blocks 2048 with error 28
EXT4-fs (loop6): This should not happen!! Data will be lost