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BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff86e720e8 of 8 bytes by task 22487 on cpu 0:
 data_alloc+0x310/0x390 kernel/printk/printk_ringbuffer.c:1129
 prb_reserve+0x8d7/0xae0 kernel/printk/printk_ringbuffer.c:1724
 vprintk_store+0x54a/0x910 kernel/printk/printk.c:2354
 vprintk_emit+0x1a4/0x600 kernel/printk/printk.c:2455
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2494
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2504
 __ext4_msg+0x1aa/0x1c0 fs/ext4/super.c:995
 mpage_map_and_submit_extent fs/ext4/inode.c:2511 [inline]
 ext4_do_writepages+0x1d89/0x2840 fs/ext4/inode.c:2937
 ext4_writepages+0x18f/0x320 fs/ext4/inode.c:3031
 do_writepages+0x1c6/0x310 mm/page-writeback.c:2575
 __writeback_single_inode+0x80/0x720 fs/fs-writeback.c:1762
 writeback_sb_inodes+0x4fe/0xaf0 fs/fs-writeback.c:2054
 wb_writeback+0x25f/0x5d0 fs/fs-writeback.c:2239
 wb_do_writeback fs/fs-writeback.c:2386 [inline]
 wb_workfn+0x1a5/0x970 fs/fs-writeback.c:2426
 process_one_work kernel/workqueue.c:3288 [inline]
 process_scheduled_works+0x513/0xa10 kernel/workqueue.c:3371
 worker_thread+0x58a/0x780 kernel/workqueue.c:3452
 kthread+0x22a/0x280 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffffff86e720e8 of 16 bytes by task 2990 on cpu 1:
 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+0x164/0x560 kernel/printk/printk.c:1611
 do_syslog+0x52b/0x7f0 kernel/printk/printk.c:1763
 __do_sys_syslog kernel/printk/printk.c:1855 [inline]
 __se_sys_syslog kernel/printk/printk.c:1853 [inline]
 __x64_sys_syslog+0x41/0x50 kernel/printk/printk.c:1853
 x64_sys_call+0x2b9e/0x3020 arch/x86/include/generated/asm/syscalls_64.h:104
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 2990 Comm: klogd Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
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