loop2: detected capacity change from 0 to 512
==================================================================
BUG: KCSAN: data-race in data_push_tail / vsnprintf

write to 0xffffffff88e66cd0 of 1 bytes by task 7662 on cpu 0:
 vsnprintf+0x84d/0x8a0 lib/vsprintf.c:-1
 vscnprintf+0x42/0x90 lib/vsprintf.c:2917
 printk_sprint+0x30/0x2d0 kernel/printk/printk.c:2216
 vprintk_store+0x583/0x860 kernel/printk/printk.c:2336
 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
 set_capacity_and_notify+0x155/0x200 block/genhd.c:93
 loop_set_size+0x2e/0x70 drivers/block/loop.c:210
 loop_configure+0x89c/0xa30 drivers/block/loop.c:1120
 lo_ioctl+0x5fa/0x1570 drivers/block/loop.c:-1
 blkdev_ioctl+0x35b/0x450 block/ioctl.c:698
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0xc9/0x140 fs/ioctl.c:892
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:892
 x64_sys_call+0x168d/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff88e66cd0 of 8 bytes by task 7664 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
 set_capacity_and_notify+0x155/0x200 block/genhd.c:93
 loop_set_size+0x2e/0x70 drivers/block/loop.c:210
 loop_configure+0x89c/0xa30 drivers/block/loop.c:1120
 lo_ioctl+0x5fa/0x1570 drivers/block/loop.c:-1
 blkdev_ioctl+0x35b/0x450 block/ioctl.c:698
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0xc9/0x140 fs/ioctl.c:892
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:892
 x64_sys_call+0x168d/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000ffffe985 -> 0x00000000ffffe900

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 7664 Comm: syz.2.1303 Not tainted 6.14.0-syzkaller-13423-ga8662bcd2ff1 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
==================================================================
EXT4-fs (loop2): feature flags set on rev 0 fs, running e2fsck is recommended
EXT4-fs (loop2): mounting ext2 file system using the ext4 subsystem
EXT4-fs (loop2): warning: checktime reached, running e2fsck is recommended
[EXT4 FS bs=4096, gc=1, bpg=32768, ipg=32, mo=a042c01c, mo2=0002]
System zones: 0-2, 18-18, 34-34
EXT4-fs warning (device loop2): ext4_update_dynamic_rev:1132: updating to rev 1 because of new feature flag, running e2fsck is recommended
EXT4-fs (loop2): 1 truncate cleaned up
EXT4-fs (loop2): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: none.