[PATCH 02/27] sched/isolation: Introduce housekeeping per-cpu rwsem

[Frederic Weisbecker <frederic@kernel.org>]

The HK_TYPE_DOMAIN isolation cpumask, and further the
HK_TYPE_KERNEL_NOISE cpumask will be made modifiable at runtime in the
future.

The affected subsystems will need to synchronize against those cpumask
changes so that:

* The reader get a coherent snapshot
* The housekeeping subsystem can safely propagate a cpumask update to
  the susbsytems after it has been published.

Protect against readsides that can sleep with per-cpu rwsem. Updates are
expected to be very rare given that CPU isolation is a niche usecase and
related cpuset setup happen only in preparation work. On the other hand
read sides can occur in more frequent paths.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 include/linux/sched/isolation.h |  7 +++++++
 kernel/sched/isolation.c        | 12 ++++++++++++
 kernel/sched/sched.h            |  1 +
 3 files changed, 20 insertions(+)

diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
index f98ba0d71c52..8de4f625a5c1 100644
--- a/include/linux/sched/isolation.h
+++ b/include/linux/sched/isolation.h
@@ -41,6 +41,9 @@ static inline bool housekeeping_cpu(int cpu, enum hk_type type)
 		return true;
 }
 
+extern void housekeeping_lock(void);
+extern void housekeeping_unlock(void);
+
 extern void __init housekeeping_init(void);
 
 #else
@@ -73,6 +76,8 @@ static inline bool housekeeping_cpu(int cpu, enum hk_type type)
 	return true;
 }
 
+static inline void housekeeping_lock(void) { }
+static inline void housekeeping_unlock(void) { }
 static inline void housekeeping_init(void) { }
 #endif /* CONFIG_CPU_ISOLATION */
 
@@ -84,4 +89,6 @@ static inline bool cpu_is_isolated(int cpu)
 	       cpuset_cpu_is_isolated(cpu);
 }
 
+DEFINE_LOCK_GUARD_0(housekeeping, housekeeping_lock(), housekeeping_unlock())
+
 #endif /* _LINUX_SCHED_ISOLATION_H */
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 83cec3853864..8c02eeccea3b 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -18,12 +18,24 @@ static cpumask_var_t housekeeping_cpumasks[HK_TYPE_MAX];
 unsigned long housekeeping_flags;
 EXPORT_SYMBOL_GPL(housekeeping_flags);
 
+DEFINE_STATIC_PERCPU_RWSEM(housekeeping_pcpu_lock);
+
 bool housekeeping_enabled(enum hk_type type)
 {
 	return !!(housekeeping_flags & BIT(type));
 }
 EXPORT_SYMBOL_GPL(housekeeping_enabled);
 
+void housekeeping_lock(void)
+{
+	percpu_down_read(&housekeeping_pcpu_lock);
+}
+
+void housekeeping_unlock(void)
+{
+	percpu_up_read(&housekeeping_pcpu_lock);
+}
+
 int housekeeping_any_cpu(enum hk_type type)
 {
 	int cpu;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 475bb5998295..0cdb560ef2f3 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -46,6 +46,7 @@
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/mutex_api.h>
+#include <linux/percpu-rwsem.h>
 #include <linux/plist.h>
 #include <linux/poll.h>
 #include <linux/proc_fs.h>
-- 
2.48.1