syzbot

BUG: KCSAN: data-race in _prb_read_valid / prb_reserve

write to 0xffffffff868c8ac8 of 8 bytes by task 14835 on cpu 1:
 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
 printk_stack_address arch/x86/kernel/dumpstack.c:72 [inline]
 show_trace_log_lvl+0x300/0x3d0 arch/x86/kernel/dumpstack.c:284
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0xf6/0x150 lib/dump_stack.c:120
 dump_stack+0x15/0x1a lib/dump_stack.c:129
 fail_dump lib/fault-inject.c:73 [inline]
 should_fail_ex+0x261/0x270 lib/fault-inject.c:174
 should_fail+0xb/0x10 lib/fault-inject.c:184
 should_fail_usercopy+0x1a/0x20 lib/fault-inject-usercopy.c:37
 strncpy_from_user+0x25/0x230 lib/strncpy_from_user.c:118
 alloc_name mm/memfd.c:405 [inline]
 __do_sys_memfd_create mm/memfd.c:470 [inline]
 __se_sys_memfd_create+0x218/0x5a0 mm/memfd.c:458
 __x64_sys_memfd_create+0x31/0x40 mm/memfd.c:458
 x64_sys_call+0x1163/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:320
 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 0xffffffff868c8ac8 of 8 bytes by task 14831 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:486 [inline]
 prb_first_seq kernel/printk/printk_ringbuffer.c:1957 [inline]
 _prb_read_valid+0x471/0x710 kernel/printk/printk_ringbuffer.c:2114
 prb_read_valid_info+0x6c/0x90 kernel/printk/printk_ringbuffer.c:2219
 find_first_fitting_seq+0x1c1/0x320 kernel/printk/printk.c:1589
 syslog_print_all+0x122/0x3f0 kernel/printk/printk.c:1721
 do_syslog+0x44a/0x810 kernel/printk/printk.c:1799
 __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: 0x000000000000088d -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 14831 Comm: syz.1.3899 Not tainted 6.14.0-syzkaller-12456-gacc4d5ff0b61 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
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