syzbot


KCSAN: data-race in futex_hash_allocate / futex_hash_allocate

Status: moderation: reported on 2025/08/16 04:09
Subsystems: kernel
[Documentation on labels]
Reported-by: syzbot+40d931f0550dafcc74fd@syzkaller.appspotmail.com
First crash: 4d11h, last: 4d11h

Sample crash report:
==================================================================
BUG: KCSAN: data-race in futex_hash_allocate / futex_hash_allocate

read-write to 0xffff88810005a3a8 of 8 bytes by task 13456 on cpu 1:
 futex_hash_allocate+0x60a/0x960 kernel/futex/core.c:1831
 futex_hash_prctl+0xd9/0xf0 kernel/futex/core.c:1950
 __do_sys_prctl kernel/sys.c:2806 [inline]
 __se_sys_prctl+0xc72/0x1300 kernel/sys.c:2455
 __x64_sys_prctl+0x67/0x80 kernel/sys.c:2455
 x64_sys_call+0x20cf/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:158
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810005a3a8 of 8 bytes by task 13450 on cpu 0:
 futex_pivot_pending kernel/futex/core.c:1751 [inline]
 futex_hash_allocate+0x591/0x960 kernel/futex/core.c:1821
 futex_hash_prctl+0xd9/0xf0 kernel/futex/core.c:1950
 __do_sys_prctl kernel/sys.c:2806 [inline]
 __se_sys_prctl+0xc72/0x1300 kernel/sys.c:2455
 __x64_sys_prctl+0x67/0x80 kernel/sys.c:2455
 x64_sys_call+0x20cf/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:158
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff88811e4606c0 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 13450 Comm: syz.5.3403 Not tainted 6.17.0-rc1-syzkaller-00165-gee94b00c1a64 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/08/16 04:09 upstream ee94b00c1a64 1804e95e .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in futex_hash_allocate / futex_hash_allocate
* Struck through repros no longer work on HEAD.