rcu-tasks: Fix access non-existent percpu rtpcp variable in rcu_tasks_need_gpcb()

In the Linux kernel, the following vulnerability has been resolved:

rcu-tasks: Fix access non-existent percpu rtpcp variable in rcu_tasks_need_gpcb()

For kernels built with CONFIG_FORCE_NR_CPUS=y, the nr_cpu_ids is

defined as NR_CPUS instead of the number of possible cpus, this

will cause the following system panic:

smpboot: Allowing 4 CPUs, 0 hotplug CPUs

...

setup_percpu: NR_CPUS:512 nr_cpumask_bits:512 nr_cpu_ids:512 nr_node_ids:1

...

BUG: unable to handle page fault for address: ffffffff9911c8c8

Oops: 0000 [#1] PREEMPT SMP PTI

CPU: 0 PID: 15 Comm: rcu_tasks_trace Tainted: G W

6.6.21 #1 5dc7acf91a5e8e9ac9dcfc35bee0245691283ea6

RIP: 0010:rcu_tasks_need_gpcb+0x25d/0x2c0

RSP: 0018:ffffa371c00a3e60 EFLAGS: 00010082

CR2: ffffffff9911c8c8 CR3: 000000040fa20005 CR4: 00000000001706f0

Call Trace:

<TASK>

? __die+0x23/0x80

? page_fault_oops+0xa4/0x180

? exc_page_fault+0x152/0x180

? asm_exc_page_fault+0x26/0x40

? rcu_tasks_need_gpcb+0x25d/0x2c0

? __pfx_rcu_tasks_kthread+0x40/0x40

rcu_tasks_one_gp+0x69/0x180

rcu_tasks_kthread+0x94/0xc0

kthread+0xe8/0x140

? __pfx_kthread+0x40/0x40

ret_from_fork+0x34/0x80

? __pfx_kthread+0x40/0x40

ret_from_fork_asm+0x1b/0x80

</TASK>

Considering that there may be holes in the CPU numbers, use the

maximum possible cpu number, instead of nr_cpu_ids, for configuring

enqueue and dequeue limits.

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