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BUG: KCSAN: data-race in _prb_read_valid / prb_reserve_in_last

write to 0xffffffff86a796a0 of 8 bytes by task 4288 on cpu 1:
 data_realloc kernel/printk/printk_ringbuffer.c:1228 [inline]
 prb_reserve_in_last+0x9f1/0xb30 kernel/printk/printk_ringbuffer.c:1495
 vprintk_store+0x457/0x910 kernel/printk/printk.c:2276
 vprintk_emit+0x1a4/0x600 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
 show_free_areas mm/show_mem.c:299 [inline]
 __show_mem+0xce3/0x1470 mm/show_mem.c:408
 warn_alloc_show_mem mm/page_alloc.c:4004 [inline]
 warn_alloc+0x1a1/0x1c0 mm/page_alloc.c:4030
 __vmalloc_node_range_noprof+0x2b6/0x12b0 mm/vmalloc.c:4016
 __vmalloc_node_noprof mm/vmalloc.c:4111 [inline]
 vzalloc_noprof+0x82/0xb0 mm/vmalloc.c:4189
 n_tty_open+0x1b/0xd0 drivers/tty/n_tty.c:1890
 tty_ldisc_open drivers/tty/tty_ldisc.c:432 [inline]
 tty_ldisc_failto drivers/tty/tty_ldisc.c:477 [inline]
 tty_ldisc_restore+0x11c/0x440 drivers/tty/tty_ldisc.c:494
 tty_set_ldisc+0x209/0x380 drivers/tty/tty_ldisc.c:567
 tiocsetd+0x51/0x60 drivers/tty/tty_io.c:2429
 tty_ioctl+0xa78/0xb80 drivers/tty/tty_io.c:2728
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
 x64_sys_call+0x14b0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86a79698 of 16 bytes by task 2991 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:496 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1931 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1979 [inline]
 _prb_read_valid+0x1bc/0x950 kernel/printk/printk_ringbuffer.c:2170
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2242
 syslog_print+0x258/0x560 kernel/printk/printk.c:1626
 do_syslog+0x52b/0x7f0 kernel/printk/printk.c:1761
 __do_sys_syslog kernel/printk/printk.c:1853 [inline]
 __se_sys_syslog kernel/printk/printk.c:1851 [inline]
 __x64_sys_syslog+0x41/0x50 kernel/printk/printk.c:1851
 x64_sys_call+0x27ce/0x3000 arch/x86/include/generated/asm/syscalls_64.h:104
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 2991 Comm: klogd Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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