syzbot

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BUG: KCSAN: data-race in _prb_read_valid / prb_reserve

write to 0xffffffff869184a8 of 88 bytes by task 28683 on cpu 1:
 prb_reserve+0x695/0xaf0 kernel/printk/printk_ringbuffer.c:1651
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2299
 vprintk_emit+0x10d/0x580 kernel/printk/printk.c:2399
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2438
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2448
 __ext4_msg+0x135/0x1a0 fs/ext4/super.c:992
 ext4_parse_param+0x7c1/0xf10 fs/ext4/super.c:2191
 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+0x216/0x660 fs/namespace.c:3723
 path_mount+0x4a5/0xb70 fs/namespace.c:4037
 do_mount fs/namespace.c:4050 [inline]
 __do_sys_mount fs/namespace.c:4238 [inline]
 __se_sys_mount+0x28c/0x2e0 fs/namespace.c:4215
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4215
 x64_sys_call+0x2b51/0x3000 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff869184a8 of 8 bytes by task 28664 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:483 [inline]
 prb_first_seq kernel/printk/printk_ringbuffer.c:1975 [inline]
 _prb_read_valid+0x383/0x920 kernel/printk/printk_ringbuffer.c:2132
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2203
 __console_flush_and_unlock kernel/printk/printk.c:3277 [inline]
 console_unlock+0x164/0x2e0 kernel/printk/printk.c:3298
 class_console_lock_destructor include/linux/console.h:669 [inline]
 con_flush_chars+0xb2/0x1b0 drivers/tty/vt/vt.c:3636
 n_tty_write+0x93d/0xb40 drivers/tty/n_tty.c:2393
 iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
 file_tty_write+0x378/0x690 drivers/tty/tty_io.c:1081
 tty_write+0x25/0x30 drivers/tty/tty_io.c:1102
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x52a/0x960 fs/read_write.c:686
 ksys_write+0xda/0x1a0 fs/read_write.c:738
 __do_sys_write fs/read_write.c:749 [inline]
 __se_sys_write fs/read_write.c:746 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:746
 x64_sys_call+0x2802/0x3000 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x000000000000374d -> 0x000000000000574d

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 28664 Comm: syz.2.7516 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
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