[moderation] [kernel?] KCSAN: data-race in futex_hash_allocate / futex_hash_allocate (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: dc855b77719f Merge tag 'irq-drivers-2026-02-09' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=163d365a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=ed0e3ea32b528eea
dashboard link: https://syzkaller.appspot.com/bug?extid=2da0e883a5ad64e5e3ce
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [andre...@igalia.com da...@stgolabs.net dvh...@infradead.org linux-...@vger.kernel.org mi...@redhat.com pet...@infradead.org tg...@kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/aebc7a8edb2f/disk-dc855b77.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ca4d10e847b9/vmlinux-dc855b77.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2e8a563693dd/bzImage-dc855b77.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2da0e8...@syzkaller.appspotmail.com

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


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