[moderation] [kernel?] KCSAN: data-race in futex_hash / futex_hash_allocate

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 69fd6b99b8f8 Merge tag 'perf_urgent_for_v6.17_rc3' of git:..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=146bba34580000
kernel config: https://syzkaller.appspot.com/x/.config?x=86a2212b48ce4ce2
dashboard link: https://syzkaller.appspot.com/bug?extid=0f28bfb72b88a66d50d5
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
CC: [andre...@igalia.com da...@stgolabs.net dvh...@infradead.org linux-...@vger.kernel.org mi...@redhat.com pet...@infradead.org tg...@linutronix.de]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2534b4011026/disk-69fd6b99.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e947565dc9d9/vmlinux-69fd6b99.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0a95d7762086/bzImage-69fd6b99.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0f28bf...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in futex_hash / futex_hash_allocate

write to 0xffff888109700128 of 8 bytes by task 17094 on cpu 1:
futex_pivot_hash kernel/futex/core.c:268 [inline]
futex_hash+0x121/0x200 kernel/futex/core.c:315
class_hb_constructor kernel/futex/futex.h:240 [inline]
futex_wake+0xdd/0x360 kernel/futex/waitwake.c:172
do_futex+0x323/0x380 kernel/futex/syscalls.c:107
__do_sys_futex kernel/futex/syscalls.c:179 [inline]
__se_sys_futex+0x2ed/0x360 kernel/futex/syscalls.c:160
__x64_sys_futex+0x78/0x90 kernel/futex/syscalls.c:160
x64_sys_call+0x2e39/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:203
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 0xffff888109700128 of 8 bytes by task 17102 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: 0xffff88815fa00000 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 17102 Comm: syz.8.24448 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.