On Mon, Aug 22, 2022 at 02:08:38PM -0400, Joel Fernandes wrote:
> On Sun, Aug 21, 2022 at 10:16 PM Pingfan Liu <kernelfans@xxxxxxxxx> wrote:
> >
> > In order to support parallel, rcu_state.n_online_cpus should be
> > atomic_dec()
>
> What does Parallel mean? Is that some kexec terminology?
>
'Parallel' means concurrent. It is not a kexec terminology, instead,
should be SMP.
Thanks,
Pingfan
> Thanks,
>
> - Joel
>
> >
> > Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
> > Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> > Cc: Frederic Weisbecker <frederic@xxxxxxxxxx>
> > Cc: Neeraj Upadhyay <quic_neeraju@xxxxxxxxxxx>
> > Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> > Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
> > Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Steven Price <steven.price@xxxxxxx>
> > Cc: "Peter Zijlstra
> > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > Cc: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> > Cc: "Jason A. Donenfeld" <Jason@xxxxxxxxx>
> > To: linux-kernel@xxxxxxxxxxxxxxx
> > To: rcu@xxxxxxxxxxxxxxx
> > ---
> > kernel/cpu.c | 1 +
> > kernel/rcu/tree.c | 3 ++-
> > 2 files changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/cpu.c b/kernel/cpu.c
> > index 1261c3f3be51..90debbe28e85 100644
> > --- a/kernel/cpu.c
> > +++ b/kernel/cpu.c
> > @@ -1872,6 +1872,7 @@ static struct cpuhp_step cpuhp_hp_states[] = {
> > .name = "RCU/tree:prepare",
> > .startup.single = rcutree_prepare_cpu,
> > .teardown.single = rcutree_dead_cpu,
> > + .support_kexec_parallel = true,
> > },
> > /*
> > * On the tear-down path, timers_dead_cpu() must be invoked
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 79aea7df4345..07d31e16c65e 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -2168,7 +2168,8 @@ int rcutree_dead_cpu(unsigned int cpu)
> > if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
> > return 0;
> >
> > - WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1);
> > + /* Hot remove path allows parallel, while Hot add races against remove on lock */
> > + atomic_dec((atomic_t *)&rcu_state.n_online_cpus);
> > /* Adjust any no-longer-needed kthreads. */
> > rcu_boost_kthread_setaffinity(rnp, -1);
> > // Stop-machine done, so allow nohz_full to disable tick.
> > --
> > 2.31.1
> >
