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

write to 0xffffffff868870b8 of 8 bytes by task 25745 on cpu 1:
 data_alloc+0x31c/0x390 kernel/printk/printk_ringbuffer.c:1130
 prb_reserve+0x8d7/0xad0 kernel/printk/printk_ringbuffer.c:1724
 vprintk_store+0x53c/0x830 kernel/printk/printk.c:2302
 vprintk_emit+0x15a/0x5c0 kernel/printk/printk.c:2402
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2441
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2451
 logfc+0x2cb/0x2e0 fs/fs_context.c:-1
 fs_param_bad_value fs/fs_parser.c:196 [inline]
 fs_param_is_u32+0x121/0x150 fs/fs_parser.c:-1
 __fs_parse+0x29a/0x420 fs/fs_parser.c:129
 fs_parse include/linux/fs_parser.h:76 [inline]
 v9fs_parse_param+0x63/0x900 fs/9p/v9fs.c:223
 vfs_parse_fs_param+0x142/0x2a0 fs/fs_context.c:146
 vfs_parse_fs_qstr fs/fs_context.c:187 [inline]
 vfs_parse_fs_string include/linux/fs_context.h:142 [inline]
 vfs_parse_monolithic_sep+0x1a3/0x220 fs/fs_context.c:227
 generic_parse_monolithic+0x24/0x30 fs/fs_context.c:255
 parse_monolithic_mount_data+0x46/0x60 fs/fs_context.c:720
 do_new_mount+0x216/0x6a0 fs/namespace.c:3708
 path_mount+0x4ab/0xb80 fs/namespace.c:4022
 do_mount fs/namespace.c:4035 [inline]
 __do_sys_mount fs/namespace.c:4224 [inline]
 __se_sys_mount+0x28c/0x2e0 fs/namespace.c:4201
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4201
 x64_sys_call+0x2cca/0x3000 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff868870b8 of 8 bytes by task 25751 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:496 [inline]
 desc_push_tail kernel/printk/printk_ringbuffer.c:792 [inline]
 desc_reserve kernel/printk/printk_ringbuffer.c:938 [inline]
 prb_reserve+0x207/0xad0 kernel/printk/printk_ringbuffer.c:1674
 vprintk_store+0x53c/0x830 kernel/printk/printk.c:2302
 vprintk_emit+0x15a/0x5c0 kernel/printk/printk.c:2402
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2441
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2451
 __ext4_error_inode+0x2ca/0x3f0 fs/ext4/super.c:853
 __ext4_ext_check+0x4b8/0x720 fs/ext4/extents.c:507
 ext4_ext_check_inode+0x46/0x60 fs/ext4/extents.c:523
 __ext4_iget+0x2039/0x2350 fs/ext4/inode.c:5424
 ext4_lookup+0x15e/0x390 fs/ext4/namei.c:1785
 lookup_open fs/namei.c:4422 [inline]
 open_last_lookups fs/namei.c:4549 [inline]
 path_openat+0xed5/0x23b0 fs/namei.c:4793
 do_filp_open+0x109/0x230 fs/namei.c:4823
 do_sys_openat2+0xa6/0x150 fs/open.c:1430
 do_sys_open fs/open.c:1436 [inline]
 __do_sys_openat fs/open.c:1452 [inline]
 __se_sys_openat fs/open.c:1447 [inline]
 __x64_sys_openat+0xf2/0x120 fs/open.c:1447
 x64_sys_call+0x2b07/0x3000 arch/x86/include/generated/asm/syscalls_64.h:258
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x000000000018d478 -> 0x00000000002494e8

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 25751 Comm: syz.1.15680 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================
EXT4-fs error (device loop1): ext4_ext_check_inode:523: inode #16: comm syz.1.15680: pblk 0 bad header/extent: invalid eh_max - magic f30a, entries 7, max 0(0), depth 0(0)
EXT4-fs (loop1): Remounting filesystem read-only