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

Alex Belits
2020-12-04T00:56:14Z

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@marvell.com>
> >
> > 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@marvell.com>
> > [abelits@marvell.com: updated, only exclude CPUs running isolated
> > tasks]
> > Signed-off-by: Alex Belits <abelits@marvell.com>
> > ---
> > 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().

--
Alex