loop8: detected capacity change from 0 to 1024
EXT4-fs: Ignoring removed nomblk_io_submit option
EXT4-fs (loop8): mounted filesystem 00000000-0000-0006-0000-000000000000 r/w without journal. Quota mode: none.
==================================================================
BUG: KCSAN: data-race in data_alloc / data_push_tail

write to 0xffffffff8938a120 of 8 bytes by task 13774 on cpu 0:
 data_alloc+0x259/0x390 kernel/printk/printk_ringbuffer.c:1116
 prb_reserve+0x8d6/0xad0 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+0x1dd/0x230 block/genhd.c:93
 loop_set_size+0x2e/0x70 drivers/block/loop.c:220
 loop_configure+0x828/0x9c0 drivers/block/loop.c:1079
 lo_ioctl+0x1e1/0x13a0 drivers/block/loop.c:1534
 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+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff8938a120 of 8 bytes by task 13776 on cpu 1:
 data_make_reusable kernel/printk/printk_ringbuffer.c:608 [inline]
 data_push_tail+0x100/0x470 kernel/printk/printk_ringbuffer.c:693
 data_alloc+0x11b/0x390 kernel/printk/printk_ringbuffer.c:1089
 prb_reserve+0x8d6/0xad0 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
 __ext4_msg+0x1aa/0x1c0 fs/ext4/super.c:1001
 ext4_fill_super+0x2f90/0x37c0 fs/ext4/super.c:5839
 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:5856
 vfs_get_tree+0x57/0x1d0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]
 do_new_mount_fc fs/namespace.c:3761 [inline]
 do_new_mount+0x288/0x8d0 fs/namespace.c:3837
 path_mount+0x4d0/0xbc0 fs/namespace.c:4157
 do_mount fs/namespace.c:4170 [inline]
 __do_sys_mount fs/namespace.c:4386 [inline]
 __se_sys_mount+0x28c/0x2e0 fs/namespace.c:4363
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4363
 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/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x3ffffffffffff163 -> 0x3ffffffffffffca0

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 13776 Comm: syz.8.2706 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
==================================================================
ext4 filesystem being mounted at /236/file1 supports timestamps until 2038-01-19 (0x7fffffff)
xt_addrtype: ipv6 PROHIBIT (THROW, NAT ..) matching not supported
EXT4-fs error (device loop8): ext4_map_blocks:833: inode #15: comm syz.8.2706: lblock 0 mapped to illegal pblock 0 (length 1)