[patch v9 07/10] task isolation: enable return to userspace processing

[Marcelo Tosatti <mtosatti@redhat.com>]

The logic to disable vmstat worker thread, when entering
nohz full, does not cover all scenarios. For example, it is possible
for the following to happen:
References: <20220127172319.428529308@fuller.cnet>
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Enable processing of pending task isolation work if per-CPU vmstats
are out of sync with global vmstats.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

---
 include/linux/task_isolation.h |   22 +++++++++++++++++++++-
 kernel/task_isolation.c        |   13 +++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

Index: linux-2.6/include/linux/task_isolation.h
===================================================================
--- linux-2.6.orig/include/linux/task_isolation.h
+++ linux-2.6/include/linux/task_isolation.h
@@ -5,6 +5,9 @@
 
 #ifdef CONFIG_CPU_ISOLATION
 
+#include <linux/vmstat.h>
+#include <uapi/linux/prctl.h>
+
 struct task_isol_info {
 	/* Which features have been configured */
 	u64 conf_mask;
@@ -110,7 +113,24 @@ static inline int prctl_task_isol_activa
 
 static inline int task_isol_has_work(void)
 {
-	return 0;
+	int cpu, ret;
+	struct isol_info *i;
+
+	if (likely(current->task_isol_info == NULL))
+		return 0;
+
+	i = current->task_isol_info;
+	if (i->active_mask != ISOL_F_QUIESCE)
+		return 0;
+
+	if (!(i->quiesce_mask & ISOL_F_QUIESCE_VMSTATS))
+		return 0;
+
+	cpu = get_cpu();
+	ret = per_cpu(vmstat_dirty, cpu);
+	put_cpu();
+
+	return ret;
 }
 
 #endif /* CONFIG_CPU_ISOLATION */
Index: linux-2.6/kernel/task_isolation.c
===================================================================
--- linux-2.6.orig/kernel/task_isolation.c
+++ linux-2.6/kernel/task_isolation.c
@@ -10,7 +10,6 @@
  */
 
 #include <linux/sched.h>
-#include <linux/task_isolation.h>
 #include <linux/prctl.h>
 #include <linux/slab.h>
 #include <linux/kobject.h>
@@ -20,9 +19,17 @@
 #include <linux/sched/task.h>
 #include <linux/mm.h>
 #include <linux/vmstat.h>
+#include <linux/task_isolation.h>
 
 void __task_isol_exit(struct task_struct *tsk)
 {
+	struct task_isol_info *i;
+
+	i = tsk->task_isol_info;
+	if (!i)
+		return;
+
+	static_key_slow_dec(&vmstat_sync_enabled);
 }
 
 void __task_isol_free(struct task_struct *tsk)
@@ -41,6 +48,12 @@ static struct task_isol_info *task_isol_
 	if (unlikely(!info))
 		return ERR_PTR(-ENOMEM);
 
+	preempt_disable();
+	init_sync_vmstat();
+	preempt_enable();
+
+	static_key_slow_inc(&vmstat_sync_enabled);
+
 	return info;
 }