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

write to 0xffffffff86872500 of 8 bytes by task 17509 on cpu 0:
 data_alloc+0x290/0x2c0 kernel/printk/printk_ringbuffer.c:1096
 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+0x13a/0x1b0 fs/ext4/super.c:987
 ext4_parse_param+0x86e/0xf70 fs/ext4/super.c:2178
 vfs_parse_fs_param+0x13b/0x290 fs/fs_context.c:146
 vfs_parse_fs_string fs/fs_context.c:188 [inline]
 vfs_parse_monolithic_sep+0x19f/0x220 fs/fs_context.c:230
 generic_parse_monolithic+0x24/0x30 fs/fs_context.c:258
 parse_monolithic_mount_data+0x43/0x50 fs/fs_context.c:719
 do_new_mount+0x219/0x6b0 fs/namespace.c:3875
 path_mount+0x49b/0xb30 fs/namespace.c:4206
 do_mount fs/namespace.c:4219 [inline]
 __do_sys_mount fs/namespace.c:4430 [inline]
 __se_sys_mount+0x28f/0x2e0 fs/namespace.c:4407
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4407
 x64_sys_call+0xd11/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:166
 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 0xffffffff86872500 of 8 bytes by task 17524 on cpu 1:
 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+0x239/0xb80 kernel/printk/printk_ringbuffer.c:1619
 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: 0xfffffffffffd9a38 -> 0x00000000000861a0

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 17524 Comm: syz.5.5204 Not tainted 6.15.0-rc1-syzkaller-00288-ge618ee89561b #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
==================================================================
loop5: detected capacity change from 0 to 164
iso9660: Unknown parameter '18446744073709551615'