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Subject: sched-mmdrop-delayed.patch
From: Thomas Gleixner <tglx@linutronix.de>
Date: Mon, 06 Jun 2011 12:20:33 +0200
Needs thread context (pgd_lock) -> ifdeffed. workqueues wont work with
RT
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/mm_types.h | 4 ++++
include/linux/sched.h | 12 ++++++++++++
kernel/fork.c | 15 ++++++++++++++-
kernel/sched/core.c | 19 +++++++++++++++++--
4 files changed, 47 insertions(+), 3 deletions(-)
Index: linux-stable/include/linux/mm_types.h
===================================================================
--- linux-stable.orig/include/linux/mm_types.h
+++ linux-stable/include/linux/mm_types.h
@@ -12,6 +12,7 @@
#include <linux/completion.h>
#include <linux/cpumask.h>
#include <linux/page-debug-flags.h>
+#include <linux/rcupdate.h>
#include <linux/uprobes.h>
#include <asm/page.h>
#include <asm/mmu.h>
@@ -409,6 +410,9 @@ struct mm_struct {
struct cpumask cpumask_allocation;
#endif
struct uprobes_state uprobes_state;
+#ifdef CONFIG_PREEMPT_RT_BASE
+ struct rcu_head delayed_drop;
+#endif
};
static inline void mm_init_cpumask(struct mm_struct *mm)
Index: linux-stable/include/linux/sched.h
===================================================================
--- linux-stable.orig/include/linux/sched.h
+++ linux-stable/include/linux/sched.h
@@ -2324,12 +2324,24 @@ extern struct mm_struct * mm_alloc(void)
/* mmdrop drops the mm and the page tables */
extern void __mmdrop(struct mm_struct *);
+
static inline void mmdrop(struct mm_struct * mm)
{
if (unlikely(atomic_dec_and_test(&mm->mm_count)))
__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
+
/* mmput gets rid of the mappings and all user-space */
extern void mmput(struct mm_struct *);
/* Grab a reference to a task's mm, if it is not already going away */
Index: linux-stable/kernel/fork.c
===================================================================
--- linux-stable.orig/kernel/fork.c
+++ linux-stable/kernel/fork.c
@@ -249,7 +249,7 @@ EXPORT_SYMBOL_GPL(__put_task_struct);
#else
void __put_task_struct_cb(struct rcu_head *rhp)
{
- struct task_struct *tsk = container_of(rhp, struct task_struct, rcu);
+ struct task_struct *tsk = container_of(rhp, struct task_struct, put_rcu);
__put_task_struct(tsk);
@@ -608,6 +608,19 @@ 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
+
/*
* Decrement the use count and release all resources for an mm.
*/
Index: linux-stable/kernel/sched/core.c
===================================================================
--- linux-stable.orig/kernel/sched/core.c
+++ linux-stable/kernel/sched/core.c
@@ -1970,8 +1970,12 @@ static void finish_task_switch(struct rq
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)) {
/*
* Remove function-return probe instances associated with this
@@ -5302,6 +5306,8 @@ static int migration_cpu_stop(void *data
#ifdef CONFIG_HOTPLUG_CPU
+static DEFINE_PER_CPU(struct mm_struct *, idle_last_mm);
+
/*
* Ensures that the idle task is using init_mm right before its cpu goes
* offline.
@@ -5314,7 +5320,12 @@ void idle_task_exit(void)
if (mm != &init_mm)
switch_mm(mm, &init_mm, current);
- 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;
}
/*
@@ -5622,6 +5633,10 @@ migration_call(struct notifier_block *nf
case CPU_DEAD:
calc_load_migrate(rq);
+ if (per_cpu(idle_last_mm, cpu)) {
+ mmdrop(per_cpu(idle_last_mm, cpu));
+ per_cpu(idle_last_mm, cpu) = NULL;
+ }
break;
#endif
}
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