On Thu, Sep 15, 2022 at 01:58:24PM +0800, Pingfan Liu wrote: > During offlining, the concurrent rcutree_offline_cpu() can not be aware > of each other through ->qsmaskinitnext. But cpu_dying_mask carries such > information at that point and can be utilized. > > Besides, a trivial change which removes the redudant call to > rcu_boost_kthread_setaffinity() in rcutree_dead_cpu() since > rcutree_offline_cpu() can fully serve that purpose. > > Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx> > Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx> > Cc: David Woodhouse <dwmw@xxxxxxxxxxxx> > 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: "Jason A. Donenfeld" <Jason@xxxxxxxxx> > To: rcu@xxxxxxxxxxxxxxx > --- > kernel/rcu/tree.c | 2 -- > kernel/rcu/tree_plugin.h | 6 ++++++ > 2 files changed, 6 insertions(+), 2 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 79aea7df4345..8a829b64f5b2 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -2169,8 +2169,6 @@ int rcutree_dead_cpu(unsigned int cpu) > return 0; > > WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1); > - /* Adjust any no-longer-needed kthreads. */ > - rcu_boost_kthread_setaffinity(rnp, -1); > // Stop-machine done, so allow nohz_full to disable tick. > tick_dep_clear(TICK_DEP_BIT_RCU); > return 0; I would suggest to make this a separate change, for bisectability and readability. > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index ef6d3ae239b9..e5afc63bd97f 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -1243,6 +1243,12 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) > cpu != outgoingcpu) > cpumask_set_cpu(cpu, cm); > cpumask_and(cm, cm, housekeeping_cpumask(HK_TYPE_RCU)); > + /* > + * For concurrent offlining, bit of qsmaskinitnext is not cleared yet. > + * So resort to cpu_dying_mask, whose changes has already been visible. > + */ > + if (outgoingcpu != -1) > + cpumask_andnot(cm, cm, cpu_dying_mask); I'm not sure how the infrastructure changes in your concurrent down patchset but can the cpu_dying_mask concurrently change at this stage? Thanks. > if (cpumask_empty(cm)) > cpumask_copy(cm, housekeeping_cpumask(HK_TYPE_RCU)); > set_cpus_allowed_ptr(t, cm); > -- > 2.31.1 >
