==================================================================
BUG: KCSAN: data-race in data_alloc / prb_reserve

write to 0xffffffff86877760 of 8 bytes by task 29909 on cpu 1:
 data_alloc+0x27d/0x2b0 kernel/printk/printk_ringbuffer.c:1096
 prb_reserve+0x808/0xaf0 kernel/printk/printk_ringbuffer.c:1669
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2326
 vprintk_emit+0x178/0x650 kernel/printk/printk.c:2426
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2465
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2475
 ext4_setup_super+0x572/0x580 fs/ext4/super.c:3108
 __ext4_fill_super fs/ext4/super.c:5524 [inline]
 ext4_fill_super+0x27d4/0x34e0 fs/ext4/super.c:5726
 get_tree_bdev_flags+0x28e/0x300 fs/super.c:1636
 get_tree_bdev+0x1f/0x30 fs/super.c:1659
 ext4_get_tree+0x1c/0x30 fs/ext4/super.c:5758
 vfs_get_tree+0x57/0x1d0 fs/super.c:1759
 do_new_mount+0x207/0x680 fs/namespace.c:3881
 path_mount+0x4a4/0xb20 fs/namespace.c:4208
 do_mount fs/namespace.c:4221 [inline]
 __do_sys_mount fs/namespace.c:4432 [inline]
 __se_sys_mount+0x28f/0x2e0 fs/namespace.c:4409
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4409
 x64_sys_call+0xd36/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86877760 of 8 bytes by task 29911 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:482 [inline]
 desc_push_tail kernel/printk/printk_ringbuffer.c:778 [inline]
 desc_reserve kernel/printk/printk_ringbuffer.c:924 [inline]
 prb_reserve+0x221/0xaf0 kernel/printk/printk_ringbuffer.c:1619
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2326
 vprintk_emit+0x178/0x650 kernel/printk/printk.c:2426
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2465
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2475
 set_capacity_and_notify+0x14c/0x1f0 block/genhd.c:93
 loop_set_size+0x2e/0x70 drivers/block/loop.c:210
 loop_configure+0x7ec/0x970 drivers/block/loop.c:1067
 lo_ioctl+0x559/0x15d0 drivers/block/loop.c:-1
 blkdev_ioctl+0x352/0x440 block/ioctl.c:704
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:892
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:892
 x64_sys_call+0x19a8/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffffffffffff5230 -> 0x00000000000b6978

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 29911 Comm: syz.2.8761 Not tainted 6.15.0-rc7-syzkaller-00014-gd608703fcdd9 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================
loop2: detected capacity change from 0 to 512
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.