syzbot


KCSAN: data-race in futex_hash_allocate / futex_hash_allocate (3)

Status: moderation: reported on 2026/02/11 09:46
Subsystems: kernel
[Documentation on labels]
Reported-by: syzbot+2da0e883a5ad64e5e3ce@syzkaller.appspotmail.com
First crash: 20d, last: 20d
✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision Error
b18fd553-ae7c-443c-a970-84912b0e0b16 assessment-kcsan Benign: ✅  Confident: ✅  KCSAN: data-race in futex_hash_allocate / futex_hash_allocate (3) 2026/02/24 18:20 2026/02/24 18:20 2026/02/24 18:29 305c0ec5cd886e2d13738e28e1b2df9b0ec20fc9
0c497ce0-49eb-415e-9e55-8a5fe1f96655 assessment-kcsan 🏃 KCSAN: data-race in futex_hash_allocate / futex_hash_allocate (3) 2026/02/12 16:24 2026/02/13 12:52 3f45136dc7eb71e0f74e923b9f5ca8ecd555f59a
Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in futex_hash_allocate / futex_hash_allocate kernel 6 1 199d 199d 0/29 auto-obsoleted due to no activity on 2025/10/11 04:10
upstream KCSAN: data-race in futex_hash_allocate / futex_hash_allocate (2) kernel 6 1 140d 140d 0/29 auto-obsoleted due to no activity on 2025/12/09 12:22

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

read-write to 0xffff88810c5a74c0 of 8 bytes by task 12336 on cpu 0:
 futex_hash_allocate+0x673/0x9d0 kernel/futex/core.c:1839
 futex_hash_prctl+0xd8/0xf0 kernel/futex/core.c:1958
 __do_sys_prctl kernel/sys.c:2870 [inline]
 __se_sys_prctl+0x914/0x1320 kernel/sys.c:2519
 __x64_sys_prctl+0x67/0x80 kernel/sys.c:2519
 x64_sys_call+0x2533/0x3020 arch/x86/include/generated/asm/syscalls_64.h:158
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810c5a74c0 of 8 bytes by task 12335 on cpu 1:
 futex_pivot_pending kernel/futex/core.c:1748 [inline]
 futex_hash_allocate+0x5fa/0x9d0 kernel/futex/core.c:1829
 futex_hash_prctl+0xd8/0xf0 kernel/futex/core.c:1958
 __do_sys_prctl kernel/sys.c:2870 [inline]
 __se_sys_prctl+0x914/0x1320 kernel/sys.c:2519
 __x64_sys_prctl+0x67/0x80 kernel/sys.c:2519
 x64_sys_call+0x2533/0x3020 arch/x86/include/generated/asm/syscalls_64.h:158
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff88811bf79cc0 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 12335 Comm: syz.8.2051 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/11 09:45 upstream dc855b77719f 441e25b7 .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.