Re: [PATCH 5/8] membarrier, kthread: Use _ONCE accessors for task->mm

[Andy Lutomirski]

On 6/16/21 11:08 AM, Mathieu Desnoyers wrote:
> ----- On Jun 15, 2021, at 11:21 PM, Andy Lutomirski luto@xxxxxxxxxx wrote:
> 
>> membarrier reads cpu_rq(remote cpu)->curr->mm without locking.  Use
>> READ_ONCE() and WRITE_ONCE() to remove the data races.
> 
> I notice that kernel/exit.c:exit_mm() also has:
> 
>         current->mm = NULL;
> 
> I suspect you may want to add a WRITE_ONCE() there as well ?

Good catch.  I was thinking that exit_mm() couldn't execute concurrently
with membarrier(), but that's wrong.

--Andy