Do we need to disable preemption in flush_tlb_range()?

[Peter Zijlstra]

On Wed, Mar 14, 2018 at 01:19:01PM -0700, Vineet Gupta wrote:
> +CC Peter since we have his attention ;-)

Yeah, timezone collision there, I typically sleep at 1am ;-)

> On 03/01/2018 07:13 AM, Alexey Brodkin wrote:
> > Hi Vineet,
> > 
> > Just noticed that in comments for smp_call_function_many() it is said that
> > preemption must be disabled during its execution. And that function gets executed
> > among other ways like that:
> > -------------------------->8-----------------------
> >    flush_tlb_range()
> >      -> on_each_cpu_mask()
> >           -> smp_call_function_many()
> > -------------------------->8-----------------------
> 
> In general I prefer not to - Peter what say you ?

The comment with smp_call_function_many() is correct, it relies on
preemption being disabled in a number of ways. I would expect
this_cpu_ptr() for example to complain when used with preemption
enabled (CONFIG_DEBUG_PREEMPT).