[PATCH] task_isolation: don't kick isolated CPUs with tick_nohz_full_kick_cpu()

[Yury Norov]

On top of Chris Metcalf series:
https://lkml.org/lkml/2017/11/3/589

tick_nohz_full_kick_cpu() currently interrupts CPUs that may run isolated
task. It's not desirable because that kick will kill isolated application.

The patch below adds check against task isolation in
tick_nohz_full_kick_cpu() to prevent breaking the isolation.

Signed-off-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>
---
 include/linux/isolation.h | 7 +++++++
 kernel/isolation.c        | 6 ------
 kernel/time/tick-sched.c  | 5 +++--
 3 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/include/linux/isolation.h b/include/linux/isolation.h
index b7f0a9085b13..fad606cdcd5e 100644
--- a/include/linux/isolation.h
+++ b/include/linux/isolation.h
@@ -158,6 +158,12 @@ static inline void task_isolation_user_exit(void)
 #endif
 }
 
+static inline bool is_isolation_cpu(int cpu)
+{
+	return task_isolation_map != NULL &&
+		cpumask_test_cpu(cpu, task_isolation_map);
+}
+
 #else /* !CONFIG_TASK_ISOLATION */
 static inline int task_isolation_request(unsigned int flags) { return -EINVAL; }
 static inline void task_isolation_start(void) { }
@@ -172,6 +178,7 @@ static inline void task_isolation_remote_cpumask_interrupt(
 	const struct cpumask *mask, const char *fmt, ...) { }
 static inline void task_isolation_signal(struct task_struct *task) { }
 static inline void task_isolation_user_exit(void) { }
+static inline bool is_isolation_cpu(int cpu) { return 0; }
 #endif
 
 #endif /* _LINUX_ISOLATION_H */
diff --git a/kernel/isolation.c b/kernel/isolation.c
index 1e39a1493e76..05db247924ef 100644
--- a/kernel/isolation.c
+++ b/kernel/isolation.c
@@ -41,12 +41,6 @@ static int __init task_isolation_init(void)
 }
 core_initcall(task_isolation_init)
 
-static inline bool is_isolation_cpu(int cpu)
-{
-	return task_isolation_map != NULL &&
-		cpumask_test_cpu(cpu, task_isolation_map);
-}
-
 /* Enable stack backtraces of any interrupts of task_isolation cores. */
 static bool task_isolation_debug;
 static int __init task_isolation_debug_func(char *str)
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index c026145eba2f..91928a6afd81 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -23,6 +23,7 @@
 #include <linux/sched/clock.h>
 #include <linux/sched/stat.h>
 #include <linux/sched/nohz.h>
+#include <linux/isolation.h>
 #include <linux/module.h>
 #include <linux/irq_work.h>
 #include <linux/posix-timers.h>
@@ -242,12 +243,12 @@ static void tick_nohz_full_kick(void)
 }
 
 /*
- * Kick the CPU if it's full dynticks in order to force it to
+ * Kick the CPU if it's full dynticks and not isolated in order to force it to
  * re-evaluate its dependency on the tick and restart it if necessary.
  */
 void tick_nohz_full_kick_cpu(int cpu)
 {
-	if (!tick_nohz_full_cpu(cpu))
+	if (!tick_nohz_full_cpu(cpu) || is_isolation_cpu(cpu))
 		return;
 
 	irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
-- 
2.17.1