Messages in this thread Patch in this message | | | From | Pingfan Liu <> | Subject | [RFC 06/10] rcu/hotplug: Make rcutree_dead_cpu() parallel | Date | Mon, 22 Aug 2022 10:15:16 +0800 |
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In order to support parallel, rcu_state.n_online_cpus should be atomic_dec()
Signed-off-by: Pingfan Liu <kernelfans@gmail.com> Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Steven Price <steven.price@arm.com> Cc: "Peter Zijlstra Cc: Mark Rutland <mark.rutland@arm.com> Cc: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> Cc: "Jason A. Donenfeld" <Jason@zx2c4.com> To: linux-kernel@vger.kernel.org To: rcu@vger.kernel.org --- 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
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