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BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff86a76488 of 8 bytes by task 31 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:2302
 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
 __ext4_msg+0x1aa/0x1c0 fs/ext4/super.c:990
 ext4_print_free_blocks fs/ext4/inode.c:1786 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2510 [inline]
 ext4_do_writepages+0x1ef4/0x2800 fs/ext4/inode.c:2932
 ext4_writepages+0x18f/0x320 fs/ext4/inode.c:3026
 do_writepages+0x1c6/0x310 mm/page-writeback.c:2598
 __writeback_single_inode+0x80/0x7b0 fs/fs-writeback.c:1737
 writeback_sb_inodes+0x4f4/0xb70 fs/fs-writeback.c:2030
 wb_writeback+0x24e/0x5b0 fs/fs-writeback.c:2216
 wb_do_writeback fs/fs-writeback.c:2363 [inline]
 wb_workfn+0x194/0x960 fs/fs-writeback.c:2403
 process_one_work kernel/workqueue.c:3257 [inline]
 process_scheduled_works+0x4cd/0x9d0 kernel/workqueue.c:3340
 worker_thread+0x6bc/0x8b0 kernel/workqueue.c:3421
 kthread+0x488/0x510 kernel/kthread.c:463
 ret_from_fork+0x148/0x280 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

read to 0xffffffff86a76488 of 16 bytes by task 2991 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+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: 1 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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