[PATCH 3/4] riscv: fix race when vmap stack overflow and remove shadow_stack

[Jisheng Zhang]

> >  #ifdef CONFIG_VMAP_STACK
> > -static DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)],
> > -               overflow_stack)__aligned(16);
> > -/*
> > - * shadow stack, handled_ kernel_ stack_ overflow(in kernel/entry.S) is used
> > - * to get per-cpu overflow stack(get_overflow_stack).
> > - */
> > -long shadow_stack[SHADOW_OVERFLOW_STACK_SIZE/sizeof(long)];
> > -asmlinkage unsigned long get_overflow_stack(void)
> > -{
> > -       return (unsigned long)this_cpu_ptr(overflow_stack) +
> > -               OVERFLOW_STACK_SIZE;
> > -}
> > +unsigned long overflow_stack[NR_CPUS][OVERFLOW_STACK_SIZE/sizeof(long)] __aligned(16);

If NR_CPUS is large, there's a non-trival memory waste, I have a
solution for this case, will send a new version today.

Thanks