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BUG: KCSAN: data-race in desc_read_finalized_seq / prb_reserve

write to 0xffffffff868eff50 of 8 bytes by task 20016 on cpu 0:
 prb_reserve+0x750/0xb80 kernel/printk/printk_ringbuffer.c:-1
 vprintk_store+0x552/0x860 kernel/printk/printk.c:2326
 vprintk_emit+0x1a0/0x6c0 kernel/printk/printk.c:2426
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2465
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x7f/0xb0 kernel/printk/printk.c:2475
 bio_check_eod block/blk-core.c:563 [inline]
 submit_bio_noacct+0x82e/0x930 block/blk-core.c:796
 submit_bio+0x218/0x230 block/blk-core.c:916
 mpage_bio_submit_read fs/mpage.c:75 [inline]
 mpage_read_folio+0xd8/0x110 fs/mpage.c:391
 fat_read_folio+0x1c/0x30 fs/fat/inode.c:204
 filemap_read_folio+0x2a/0x110 mm/filemap.c:2412
 filemap_fault+0x628/0xb10 mm/filemap.c:3506
 __do_fault+0xb6/0x200 mm/memory.c:4989
 do_shared_fault mm/memory.c:5473 [inline]
 do_fault mm/memory.c:5547 [inline]
 do_pte_missing mm/memory.c:4059 [inline]
 handle_pte_fault mm/memory.c:5888 [inline]
 __handle_mm_fault mm/memory.c:6031 [inline]
 handle_mm_fault+0xc92/0x2b30 mm/memory.c:6200
 do_user_addr_fault arch/x86/mm/fault.c:1388 [inline]
 handle_page_fault arch/x86/mm/fault.c:1480 [inline]
 exc_page_fault+0x296/0x650 arch/x86/mm/fault.c:1538
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
 rep_movs_alternative+0x4a/0x70 arch/x86/lib/copy_user_64.S:68
 copy_user_generic arch/x86/include/asm/uaccess_64.h:126 [inline]
 raw_copy_to_user arch/x86/include/asm/uaccess_64.h:147 [inline]
 copy_to_user_iter lib/iov_iter.c:25 [inline]
 iterate_ubuf include/linux/iov_iter.h:30 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:300 [inline]
 iterate_and_advance include/linux/iov_iter.h:328 [inline]
 _copy_to_iter+0x144/0xd10 lib/iov_iter.c:185
 copy_to_iter include/linux/uio.h:220 [inline]
 get_random_bytes_user+0x131/0x290 drivers/char/random.c:472
 __do_sys_getrandom drivers/char/random.c:1414 [inline]
 __se_sys_getrandom drivers/char/random.c:1388 [inline]
 __x64_sys_getrandom+0xba/0x190 drivers/char/random.c:1388
 x64_sys_call+0x29cd/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:319
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff868eff50 of 8 bytes by task 2991 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:486 [inline]
 desc_read_finalized_seq+0x163/0x280 kernel/printk/printk_ringbuffer.c:1874
 prb_read kernel/printk/printk_ringbuffer.c:1922 [inline]
 _prb_read_valid+0x142/0x710 kernel/printk/printk_ringbuffer.c:2113
 prb_read_valid+0x42/0x70 kernel/printk/printk_ringbuffer.c:2185
 syslog_print+0x242/0x540 kernel/printk/printk.c:1650
 do_syslog+0x3ae/0x810 kernel/printk/printk.c:1785
 __do_sys_syslog kernel/printk/printk.c:1877 [inline]
 __se_sys_syslog kernel/printk/printk.c:1875 [inline]
 __x64_sys_syslog+0x43/0x50 kernel/printk/printk.c:1875
 x64_sys_call+0x2b8f/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:104
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000001010 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 2991 Comm: klogd Not tainted 6.14.0-syzkaller-07422-gacb4f33713b9 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
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