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Subject: sched: Move mmdrop to RCU on RT
From: Thomas Gleixner <tglx@linutronix.de>
Date: Mon, 06 Jun 2011 12:20:33 +0200
Takes sleeping locks and calls into the memory allocator, so nothing
we want to do in task switch and oder atomic contexts.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/mm_types.h | 4 ++++
include/linux/sched/mm.h | 11 +++++++++++
kernel/fork.c | 13 +++++++++++++
kernel/sched/core.c | 19 +++++++++++++++++--
4 files changed, 45 insertions(+), 2 deletions(-)
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -11,6 +11,7 @@
#include <linux/completion.h>
#include <linux/cpumask.h>
#include <linux/uprobes.h>
+#include <linux/rcupdate.h>
#include <linux/page-flags-layout.h>
#include <linux/workqueue.h>
@@ -491,6 +492,9 @@ struct mm_struct {
bool tlb_flush_pending;
#endif
struct uprobes_state uprobes_state;
+#ifdef CONFIG_PREEMPT_RT_BASE
+ struct rcu_head delayed_drop;
+#endif
#ifdef CONFIG_HUGETLB_PAGE
atomic_long_t hugetlb_usage;
#endif
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -42,6 +42,17 @@ static inline void mmdrop(struct mm_stru
__mmdrop(mm);
}
+#ifdef CONFIG_PREEMPT_RT_BASE
+extern void __mmdrop_delayed(struct rcu_head *rhp);
+static inline void mmdrop_delayed(struct mm_struct *mm)
+{
+ if (atomic_dec_and_test(&mm->mm_count))
+ call_rcu(&mm->delayed_drop, __mmdrop_delayed);
+}
+#else
+# define mmdrop_delayed(mm) mmdrop(mm)
+#endif
+
static inline void mmdrop_async_fn(struct work_struct *work)
{
struct mm_struct *mm = container_of(work, struct mm_struct, async_put_work);
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -885,6 +885,19 @@ void __mmdrop(struct mm_struct *mm)
}
EXPORT_SYMBOL_GPL(__mmdrop);
+#ifdef CONFIG_PREEMPT_RT_BASE
+/*
+ * RCU callback for delayed mm drop. Not strictly rcu, but we don't
+ * want another facility to make this work.
+ */
+void __mmdrop_delayed(struct rcu_head *rhp)
+{
+ struct mm_struct *mm = container_of(rhp, struct mm_struct, delayed_drop);
+
+ __mmdrop(mm);
+}
+#endif
+
static inline void __mmput(struct mm_struct *mm)
{
VM_BUG_ON(atomic_read(&mm->mm_users));
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2785,8 +2785,12 @@ static struct rq *finish_task_switch(str
finish_arch_post_lock_switch();
fire_sched_in_preempt_notifiers(current);
+ /*
+ * We use mmdrop_delayed() here so we don't have to do the
+ * full __mmdrop() when we are the last user.
+ */
if (mm)
- mmdrop(mm);
+ mmdrop_delayed(mm);
if (unlikely(prev_state == TASK_DEAD)) {
if (prev->sched_class->task_dead)
prev->sched_class->task_dead(prev);
@@ -5612,6 +5616,8 @@ void sched_setnuma(struct task_struct *p
#endif /* CONFIG_NUMA_BALANCING */
#ifdef CONFIG_HOTPLUG_CPU
+static DEFINE_PER_CPU(struct mm_struct *, idle_last_mm);
+
/*
* Ensure that the idle task is using init_mm right before its CPU goes
* offline.
@@ -5626,7 +5632,12 @@ void idle_task_exit(void)
switch_mm(mm, &init_mm, current);
finish_arch_post_lock_switch();
}
- mmdrop(mm);
+ /*
+ * Defer the cleanup to an alive cpu. On RT we can neither
+ * call mmdrop() nor mmdrop_delayed() from here.
+ */
+ per_cpu(idle_last_mm, smp_processor_id()) = mm;
+
}
/*
@@ -5953,6 +5964,10 @@ int sched_cpu_dying(unsigned int cpu)
update_max_interval();
nohz_balance_exit_idle(cpu);
hrtick_clear(rq);
+ if (per_cpu(idle_last_mm, cpu)) {
+ mmdrop_delayed(per_cpu(idle_last_mm, cpu));
+ per_cpu(idle_last_mm, cpu) = NULL;
+ }
return 0;
}
#endif
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