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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ee94b00c1a64 Merge tag 'block-6.17-20250815' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12ff5af0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=4b9e5b4a480a9ae2
dashboard link: https://syzkaller.appspot.com/bug?extid=40d931f0550dafcc74fd
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/a391dc9e8f7c/disk-ee94b00c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/079aba4972a8/vmlinux-ee94b00c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/bfb66bde76f0/bzImage-ee94b00c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+40d931...@syzkaller.appspotmail.com

==================================================================
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
==================================================================


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[syzbot]

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