In order to support parallel, rcu_state.n_online_cpus should be
atomic_dec()
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
