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SubjectUBSAN: shift-out-of-bounds in detach_tasks

syzbot found the following issue on:

HEAD commit: 31caf8b2 Merge branch 'linus' of git://
git tree: upstream
console output:
kernel config:
dashboard link:
compiler: Debian clang version 11.0.1-2

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:

UBSAN: shift-out-of-bounds in kernel/sched/fair.c:7712:14
shift exponent 78 is too large for 64-bit type 'unsigned long'
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.11.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x125/0x19e lib/dump_stack.c:120
ubsan_epilogue lib/ubsan.c:148 [inline]
__ubsan_handle_shift_out_of_bounds+0x432/0x4d0 lib/ubsan.c:395
detach_tasks+0xd04/0x1110 kernel/sched/fair.c:7712
load_balance+0x3a06/0x5aa0 kernel/sched/fair.c:9641
rebalance_domains+0x4ca/0x9c0 kernel/sched/fair.c:10029
__do_softirq+0x318/0x714 kernel/softirq.c:343
__run_on_irqstack arch/x86/include/asm/irq_stack.h:26 [inline]
run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:77 [inline]
do_softirq_own_stack+0x9a/0xe0 arch/x86/kernel/irq_64.c:77
invoke_softirq kernel/softirq.c:226 [inline]
__irq_exit_rcu+0x1d8/0x200 kernel/softirq.c:420
irq_exit_rcu+0x5/0x20 kernel/softirq.c:432
sysvec_apic_timer_interrupt+0xe0/0xf0 arch/x86/kernel/apic/apic.c:1100
asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:635
RIP: 0010:native_save_fl arch/x86/include/asm/irqflags.h:29 [inline]
RIP: 0010:arch_local_save_flags arch/x86/include/asm/irqflags.h:70 [inline]
RIP: 0010:arch_irqs_disabled arch/x86/include/asm/irqflags.h:137 [inline]
RIP: 0010:acpi_safe_halt drivers/acpi/processor_idle.c:111 [inline]
RIP: 0010:acpi_idle_do_entry drivers/acpi/processor_idle.c:516 [inline]
RIP: 0010:acpi_idle_enter+0x3c9/0x700 drivers/acpi/processor_idle.c:647
Code: 08 31 ff e8 f9 bc 5e fd 48 83 e3 08 0f 85 06 01 00 00 e8 8a b2 64 fd e9 0c 00 00 00 e8 30 b8 5e fd 0f 00 2d 09 aa 00 06 fb f4 <9c> 8f 44 24 10 48 8d 44 24 10 48 c1 e8 03 42 80 3c 38 00 74 0a 48
RSP: 0018:ffffc90000d47dc0 EFLAGS: 00000282
RAX: 36452ebac7a23f00 RBX: 0000000000000000 RCX: ffffffff8ff8aa03
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffff88801368e800 R08: ffffffff817e80e0 R09: ffffed10023b26f1
R10: ffffed10023b26f1 R11: 0000000000000000 R12: ffff8880186a0804
R13: ffff88801368e864 R14: 1ffff110030d4100 R15: dffffc0000000000
cpuidle_enter_state+0x486/0xd50 drivers/cpuidle/cpuidle.c:237
cpuidle_enter+0x59/0x90 drivers/cpuidle/cpuidle.c:351
call_cpuidle kernel/sched/idle.c:158 [inline]
cpuidle_idle_call kernel/sched/idle.c:239 [inline]
do_idle+0x315/0x530 kernel/sched/idle.c:300
cpu_startup_entry+0x15/0x20 kernel/sched/idle.c:397

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