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BUG: KCSAN: data-race in _prb_read_valid / prb_reserve

write to 0xffffffff86933230 of 88 bytes by task 3282 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
 show_free_areas mm/show_mem.c:349 [inline]
 __show_mem+0xcf9/0x1470 mm/show_mem.c:408
 warn_alloc_show_mem mm/page_alloc.c:4004 [inline]
 warn_alloc+0x187/0x1a0 mm/page_alloc.c:4030
 __vmalloc_node_range_noprof+0x2b3/0x1310 mm/vmalloc.c:4016
 __vmalloc_node_noprof mm/vmalloc.c:4111 [inline]
 vzalloc_noprof+0x82/0xc0 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_setup+0x83/0x220 drivers/tty/tty_ldisc.c:745
 tty_init_dev+0x183/0x320 drivers/tty/tty_io.c:1431
 tty_open_by_driver drivers/tty/tty_io.c:2073 [inline]
 tty_open+0x6c7/0xaf0 drivers/tty/tty_io.c:2120
 chrdev_open+0x2eb/0x3a0 fs/char_dev.c:414
 do_dentry_open+0x54b/0xa60 fs/open.c:962
 vfs_open+0x37/0x1e0 fs/open.c:1094
 do_open fs/namei.c:4637 [inline]
 path_openat+0x1ddd/0x23b0 fs/namei.c:4796
 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

read to 0xffffffff86933230 of 8 bytes by task 2994 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:500 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1931 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1979 [inline]
 _prb_read_valid+0x1c4/0x920 kernel/printk/printk_ringbuffer.c:2170
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2242
 syslog_print+0xeb/0x540 kernel/printk/printk.c:1609
 do_syslog+0x52b/0x7e0 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+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000007c2c -> 0x0000000000009c2c

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 2994 Comm: klogd Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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