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

Marcelo Tosatti
2022-01-27T17:26:41Z

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;
}