Re: [PATCH] riscv: VMAP_STACK overflow detection thread-safe

[Deepak Gupta]

On Thu, Nov 24, 2022 at 12:26:12AM -0800, Deepak Gupta wrote:
> On Thu, Nov 24, 2022 at 09:32:19AM +0800, Guo Ren wrote:
> > > +.macro asm_per_cpu dst sym tmp
> > > +       REG_L \tmp, TASK_TI_CPU_NUM(tp)
> > > +       slli \tmp, \tmp, 0x3
> > > +       la \dst, __per_cpu_offset
> > > +       add \dst, \dst, \tmp
> > > +       REG_L \tmp, 0(\dst)
> > > +       la \dst, \sym
> > > +       add \dst, \dst, \tmp
> > Another tricky asm code of using percpu, I don't know how the percpu
> > maintenance guy thinks.
>
> On this, if you can point me to someone, I would like to get their feedback.
> While discussing this, one issue that comes in my mind is if the shift 
> of 0x3 is correct or not on 32bit systems. I don't know what's the 
> size of each entry
> in `__per_cpu_offset`. On 64bit it's 8 bytes and thus 3 bit shift.

Yes this would need a fix for 32bit.
`__per_cpu_offset` is an array of `unsigned long` and thus shift should be 2 bit
on 32bit systems.