syzbot

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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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