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

write to 0xffffffff868d64d8 of 88 bytes by task 13510 on cpu 1:
 prb_reserve+0x6e6/0xad0 kernel/printk/printk_ringbuffer.c:1690
 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
 batadv_mcast_querier_log net/batman-adv/multicast.c:-1 [inline]
 batadv_mcast_bridge_log net/batman-adv/multicast.c:817 [inline]
 batadv_mcast_mla_flags_update net/batman-adv/multicast.c:876 [inline]
 __batadv_mcast_mla_update net/batman-adv/multicast.c:920 [inline]
 batadv_mcast_mla_update+0x1761/0x1830 net/batman-adv/multicast.c:946
 process_one_work kernel/workqueue.c:3257 [inline]
 process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3340
 worker_thread+0x582/0x770 kernel/workqueue.c:3421
 kthread+0x489/0x510 kernel/kthread.c:463
 ret_from_fork+0x149/0x290 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

read to 0xffffffff868d64d8 of 8 bytes by task 28974 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:500 [inline]
 prb_first_seq kernel/printk/printk_ringbuffer.c:2014 [inline]
 _prb_read_valid+0x383/0x920 kernel/printk/printk_ringbuffer.c:2171
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2242
 printk_get_next_message+0xc8/0x510 kernel/printk/printk.c:2999
 console_emit_next_record kernel/printk/printk.c:3083 [inline]
 console_flush_one_record kernel/printk/printk.c:3215 [inline]
 console_flush_all+0x2c8/0x6c0 kernel/printk/printk.c:3289
 __console_flush_and_unlock kernel/printk/printk.c:3319 [inline]
 console_unlock+0x97/0x270 kernel/printk/printk.c:3359
 class_console_lock_destructor include/linux/console.h:737 [inline]
 do_con_write+0x28df/0x2940 drivers/tty/vt/vt.c:3243
 con_put_char+0x38/0x60 drivers/tty/vt/vt.c:3573
 tty_put_char+0x68/0xc0 drivers/tty/tty_io.c:3153
 do_output_char+0x4de/0x500 drivers/tty/n_tty.c:459
 process_output drivers/tty/n_tty.c:482 [inline]
 n_tty_write+0x8d5/0xbf0 drivers/tty/n_tty.c:2377
 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+0x2847/0x3000 arch/x86/include/generated/asm/syscalls_64.h:2
 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: 0x0000000000006b4b -> 0x0000000000008b4b

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 28974 Comm: syz.1.19086 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================