Re: [PATCH 13/33] sched/isolation: Convert housekeeping cpumasks to rcu pointers

HK_TYPE_DOMAIN's cpumask will soon be made modifiable by cpuset.
A synchronization mechanism is then needed to synchronize the updates
with the housekeeping cpumask readers.

Turn the housekeeping cpumasks into RCU pointers. Once a housekeeping
cpumask will be modified, the update side will wait for an RCU grace
period and propagate the change to interested subsystem when deemed
necessary.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 kernel/sched/isolation.c | 58 +++++++++++++++++++++++++---------------
 kernel/sched/sched.h     |  1 +
 2 files changed, 37 insertions(+), 22 deletions(-)

diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 11a623fa6320..83be49ec2b06 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c

@@ -21,7 +21,7 @@ DEFINE_STATIC_KEY_FALSE(housekeeping_overridden);
 EXPORT_SYMBOL_GPL(housekeeping_overridden);
 
 struct housekeeping {
-	cpumask_var_t cpumasks[HK_TYPE_MAX];
+	struct cpumask __rcu *cpumasks[HK_TYPE_MAX];
 	unsigned long flags;
 };
 

@@ -33,17 +33,28 @@ bool housekeeping_enabled(enum hk_type type)
 }
 EXPORT_SYMBOL_GPL(housekeeping_enabled);
 
+const struct cpumask *housekeeping_cpumask(enum hk_type type)
+{
+	if (static_branch_unlikely(&housekeeping_overridden)) {
+		if (housekeeping.flags & BIT(type)) {
+			return rcu_dereference_check(housekeeping.cpumasks[type], 1);
+		}
+	}
+	return cpu_possible_mask;
+}
+EXPORT_SYMBOL_GPL(housekeeping_cpumask);
+