[PATCH v3 05/12] smp: Free call_function_data via RCU in smpcfd_dead_cpu

[Chuyi Zhou]

Use rcu_read_lock() to protect csd in smp_call_function_many_cond() and
wait for all read critical sections to exit before releasing percpu csd
data. This is preparation for enabling preemption during csd_lock_wait()
and can prevent accessing cfd->csd data that has already been freed in
smpcfd_dead_cpu().

Signed-off-by: Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx>
---
 kernel/smp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/smp.c b/kernel/smp.c
index 9728ba55944d..32c293d8be0e 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -77,6 +77,7 @@ int smpcfd_dead_cpu(unsigned int cpu)
 {
 	struct call_function_data *cfd = &per_cpu(cfd_data, cpu);
 
+	synchronize_rcu();
 	free_cpumask_var(cfd->cpumask);
 	free_cpumask_var(cfd->cpumask_ipi);
 	free_percpu(cfd->csd);
@@ -810,6 +811,7 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
 
 	lockdep_assert_preemption_disabled();
 
+	rcu_read_lock();
 	cfd = this_cpu_ptr(&cfd_data);
 	cpumask = cfd->cpumask;
 
@@ -905,6 +907,7 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
 		}
 	}
 
+	rcu_read_unlock();
 	if (preemptible_wait)
 		free_cpumask_var(cpumask_stack);
 }
-- 
2.20.1