syzbot

loop5: detected capacity change from 0 to 1024
==================================================================
BUG: KCSAN: data-race in data_alloc / data_push_tail

write to 0xffffffff893b8248 of 8 bytes by task 22508 on cpu 0:
 data_alloc+0x240/0x380 kernel/printk/printk_ringbuffer.c:1116
 prb_reserve+0x8e3/0xaf0 kernel/printk/printk_ringbuffer.c:1727
 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
 fserror_report+0x423/0x500 fs/fserror.c:182
 fserror_report_metadata include/linux/fserror.h:67 [inline]
 __ext4_error+0x152/0x2e0 fs/ext4/super.c:834
 ext4_read_block_bitmap_nowait+0x1d5/0x670 fs/ext4/balloc.c:482
 ext4_mb_prefetch+0x156/0x220 fs/ext4/mballoc.c:2878
 ext4_mb_might_prefetch fs/ext4/mballoc.c:2918 [inline]
 ext4_mb_scan_group+0x177/0xf50 fs/ext4/mballoc.c:2963
 ext4_mb_scan_groups_linear fs/ext4/mballoc.c:1176 [inline]
 ext4_mb_scan_groups fs/ext4/mballoc.c:1208 [inline]
 ext4_mb_regular_allocator+0x5bc/0x1550 fs/ext4/mballoc.c:3062
 ext4_mb_new_blocks+0x7c7/0x1e70 fs/ext4/mballoc.c:6310
 ext4_ext_map_blocks+0xde9/0x2f30 fs/ext4/extents.c:4461
 ext4_map_create_blocks+0xd1/0x390 fs/ext4/inode.c:631
 ext4_map_blocks+0x57f/0x950 fs/ext4/inode.c:824
 ext4_getblk+0x135/0x540 fs/ext4/inode.c:992
 ext4_bread+0x28/0x110 fs/ext4/inode.c:1055
 ext4_quota_write+0x166/0x360 fs/ext4/super.c:7396
 write_blk+0x8a/0x100 fs/quota/quota_tree.c:70
 do_insert_tree+0x954/0xad0 fs/quota/quota_tree.c:407
 do_insert_tree+0x751/0xad0 fs/quota/quota_tree.c:402
 do_insert_tree+0x751/0xad0 fs/quota/quota_tree.c:402
 do_insert_tree+0x751/0xad0 fs/quota/quota_tree.c:402
 dq_insert_tree fs/quota/quota_tree.c:432 [inline]
 qtree_write_dquot+0x2b7/0x2e0 fs/quota/quota_tree.c:451
 v2_write_dquot+0xcb/0x130 fs/quota/quota_v2.c:372
 dquot_acquire+0x1bc/0x2b0 fs/quota/dquot.c:498
 ext4_acquire_dquot+0x15f/0x200 fs/ext4/super.c:7028
 dqget+0x51f/0x8b0 fs/quota/dquot.c:1002
 __dquot_initialize+0x212/0x7c0 fs/quota/dquot.c:1530
 dquot_initialize+0x1a/0x30 fs/quota/dquot.c:1592
 ext4_process_orphan+0x2d/0x1c0 fs/ext4/orphan.c:327
 ext4_orphan_cleanup+0x6a6/0xa10 fs/ext4/orphan.c:472
 __ext4_fill_super fs/ext4/super.c:5701 [inline]
 ext4_fill_super+0x33d5/0x3780 fs/ext4/super.c:5824
 get_tree_bdev_flags+0x291/0x300 fs/super.c:1634
 get_tree_bdev+0x1f/0x30 fs/super.c:1657
 ext4_get_tree+0x1c/0x30 fs/ext4/super.c:5856
 vfs_get_tree+0x57/0x1d0 fs/super.c:1694
 fc_mount fs/namespace.c:1198 [inline]
 do_new_mount_fc fs/namespace.c:3765 [inline]
 do_new_mount+0x288/0x8d0 fs/namespace.c:3841
 path_mount+0x4ad/0xb90 fs/namespace.c:4161
 do_mount fs/namespace.c:4174 [inline]
 __do_sys_mount fs/namespace.c:4390 [inline]
 __se_sys_mount+0x28c/0x2e0 fs/namespace.c:4367
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4367
 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+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff893b8248 of 8 bytes by task 22510 on cpu 1:
 data_make_reusable kernel/printk/printk_ringbuffer.c:608 [inline]
 data_push_tail+0x104/0x440 kernel/printk/printk_ringbuffer.c:693
 data_alloc+0x111/0x380 kernel/printk/printk_ringbuffer.c:1089
 prb_reserve+0x8e3/0xaf0 kernel/printk/printk_ringbuffer.c:1727
 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
 set_capacity_and_notify+0x1d5/0x230 block/genhd.c:93
 loop_set_size+0x2e/0x70 drivers/block/loop.c:220
 loop_configure+0x826/0x9c0 drivers/block/loop.c:1075
 lo_ioctl+0x1e1/0x1390 drivers/block/loop.c:1530
 blkdev_ioctl+0x387/0x460 block/ioctl.c:797
 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+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000000010d4 -> 0x0000000000001c73

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 22510 Comm: syz.5.4489 Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
==================================================================
EXT4-fs warning (device loop5): ext4_multi_mount_protect:393: Unable to create kmmpd thread for loop5.