Re: [PATCH 1/2] membarrier: add MEMBARRIER_CMD_PRIVATE_RESTART_RSEQ_ON_CPU

[Peter Oskolkov]

On Thu, Aug 6, 2020 at 6:48 AM <peterz@xxxxxxxxxxxxx> wrote:
>
> On Wed, Aug 05, 2020 at 05:08:58PM -0700, Peter Oskolkov wrote:
>
> Thanks for the Cc!

Always a pleasure!

(Sorry, included only membarrier maintainers in v1; in v2 included
both membarrier and rseq maintainers).

>
> > + * @MEMBARRIER_CMD_PRIVATE_RESTART_RSEQ_ON_CPU:
> > + *                          If a thread belonging to the current process
> > + *                          is currently in an RSEQ critical section on the
> > + *                          CPU identified by flags parameter, restart it.
> > + *                          @flags: if @flags >= 0, identifies the CPU to
> > + *                                  restart RSEQ CS on; if == -1, restarts
> > + *                                  RSEQ CSs on all CPUs.
>
> > +     } else if (cpu_id == -1) {
> > +             on_each_cpu(membarrier_rseq_ipi,
> > +                         current->group_leader, true);
>
> This is an unpriv IPI the world. That's a big no-no.

removed in v2.

>
> Double so because all you want to target is the current process, which
> you're defining as CLONE_THREAD, where the rest of this file uses
> CLONE_VM to define a process.

Use current->mm in v2 instead of current->group_leader. Is it better this way?