Re: [EXT] Re: [PATCH v5 7/9] task_isolation: don't interrupt CPUs with tick_nohz_full_kick_cpu()

[Mark Rutland]

On Fri, Dec 04, 2020 at 12:54:29AM +0000, Alex Belits wrote:
> 
> On Wed, 2020-12-02 at 14:20 +0000, Mark Rutland wrote:
> > External Email
> > 
> > -------------------------------------------------------------------
> > ---
> > On Mon, Nov 23, 2020 at 05:58:22PM +0000, Alex Belits wrote:
> > > From: Yuri Norov <ynorov@xxxxxxxxxxx>
> > > 
> > > For nohz_full CPUs the desirable behavior is to receive interrupts
> > > generated by tick_nohz_full_kick_cpu(). But for hard isolation it's
> > > obviously not desirable because it breaks isolation.
> > > 
> > > This patch adds check for it.
> > > 
> > > Signed-off-by: Yuri Norov <ynorov@xxxxxxxxxxx>
> > > [abelits@xxxxxxxxxxx: updated, only exclude CPUs running isolated
> > > tasks]
> > > Signed-off-by: Alex Belits <abelits@xxxxxxxxxxx>
> > > ---
> > >  kernel/time/tick-sched.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> > > index a213952541db..6c8679e200f0 100644
> > > --- a/kernel/time/tick-sched.c
> > > +++ b/kernel/time/tick-sched.c
> > > @@ -20,6 +20,7 @@
> > >  #include <linux/sched/clock.h>
> > >  #include <linux/sched/stat.h>
> > >  #include <linux/sched/nohz.h>
> > > +#include <linux/isolation.h>
> > >  #include <linux/module.h>
> > >  #include <linux/irq_work.h>
> > >  #include <linux/posix-timers.h>
> > > @@ -268,7 +269,8 @@ static void tick_nohz_full_kick(void)
> > >   */
> > >  void tick_nohz_full_kick_cpu(int cpu)
> > >  {
> > > -	if (!tick_nohz_full_cpu(cpu))
> > > +	smp_rmb();
> > 
> > What does this barrier pair with? The commit message doesn't mention
> > it,
> > and it's not clear in-context.
> 
> With barriers in task_isolation_kernel_enter()
> and task_isolation_exit_to_user_mode().

Please add a comment in the code as to what it pairs with.

Thanks,
Mark.