[moderation] [kernel?] KCSAN: data-race in futex_hash_allocate / futex_hash_allocate (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3a8660878839 Linux 6.18-rc1
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14177892580000
kernel config: https://syzkaller.appspot.com/x/.config?x=bafeb347352dd60e
dashboard link: https://syzkaller.appspot.com/bug?extid=92ce2cb4bc11dc019b6d
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
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/716425d8a25c/disk-3a866087.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7ef133e1ca3c/vmlinux-3a866087.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ef381199ff0e/bzImage-3a866087.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+92ce2c...@syzkaller.appspotmail.com

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

read-write to 0xffff88810005d768 of 8 bytes by task 20201 on cpu 0:
futex_hash_allocate+0x67a/0x9d0 kernel/futex/core.c:1839
futex_hash_prctl+0xd9/0xf0 kernel/futex/core.c:1958
__do_sys_prctl kernel/sys.c:2869 [inline]
__se_sys_prctl+0xc88/0x12e0 kernel/sys.c:2518
__x64_sys_prctl+0x67/0x80 kernel/sys.c:2518
x64_sys_call+0x20cf/0x3000 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 0xffff88810005d768 of 8 bytes by task 20203 on cpu 1:
futex_pivot_pending kernel/futex/core.c:1748 [inline]
futex_hash_allocate+0x601/0x9d0 kernel/futex/core.c:1829
futex_hash_prctl+0xd9/0xf0 kernel/futex/core.c:1958
__do_sys_prctl kernel/sys.c:2869 [inline]
__se_sys_prctl+0xc88/0x12e0 kernel/sys.c:2518
__x64_sys_prctl+0x67/0x80 kernel/sys.c:2518
x64_sys_call+0x20cf/0x3000 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: 0xffff8881192057c0 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 20203 Comm: syz.3.5268 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================


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