From: Paul E. McKenney paulmck@kernel.org
[ Upstream commit 15d44dfa40305da1648de4bf001e91cc63148725 ]
Currently, rcu_cpu_starting() is written so that it might be invoked with interrupts enabled. However, it is always called when interrupts are disabled, either by rcu_init(), notify_cpu_starting(), or from a call point prior to the call to notify_cpu_starting().
But why bother requiring that interrupts be disabled? The purpose is to allow the rcu_data structure's ->beenonline flag to be set after all early processing has completed for the incoming CPU, thus allowing this flag to be used to determine when workqueues have been set up for the incoming CPU, while still allowing this flag to be used as a diagnostic within rcu_core().
This commit therefore makes rcu_cpu_starting() rely on interrupts being disabled.
Signed-off-by: Paul E. McKenney paulmck@kernel.org Stable-dep-of: 401b0de3ae4f ("rcu-tasks: Stop rcu_tasks_invoke_cbs() from using never-onlined CPUs") Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/rcu/tree.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index d03122f90cc48..5b5ed772f620a 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -4223,15 +4223,16 @@ int rcutree_offline_cpu(unsigned int cpu) * Note that this function is special in that it is invoked directly * from the incoming CPU rather than from the cpuhp_step mechanism. * This is because this function must be invoked at a precise location. + * This incoming CPU must not have enabled interrupts yet. */ void rcu_cpu_starting(unsigned int cpu) { - unsigned long flags; unsigned long mask; struct rcu_data *rdp; struct rcu_node *rnp; bool newcpu;
+ lockdep_assert_irqs_disabled(); rdp = per_cpu_ptr(&rcu_data, cpu); if (rdp->cpu_started) return; @@ -4239,7 +4240,6 @@ void rcu_cpu_starting(unsigned int cpu)
rnp = rdp->mynode; mask = rdp->grpmask; - local_irq_save(flags); arch_spin_lock(&rcu_state.ofl_lock); rcu_dynticks_eqs_online(); raw_spin_lock(&rcu_state.barrier_lock); @@ -4258,17 +4258,16 @@ void rcu_cpu_starting(unsigned int cpu) /* An incoming CPU should never be blocking a grace period. */ if (WARN_ON_ONCE(rnp->qsmask & mask)) { /* RCU waiting on incoming CPU? */ /* rcu_report_qs_rnp() *really* wants some flags to restore */ - unsigned long flags2; + unsigned long flags;
- local_irq_save(flags2); + local_irq_save(flags); rcu_disable_urgency_upon_qs(rdp); /* Report QS -after- changing ->qsmaskinitnext! */ - rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags2); + rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); } else { raw_spin_unlock_rcu_node(rnp); } arch_spin_unlock(&rcu_state.ofl_lock); - local_irq_restore(flags); smp_mb(); /* Ensure RCU read-side usage follows above initialization. */ }