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Date: Mon, 12 May 2014 01:33:54 +0200
From: Frederic Weisbecker <fweisbec@...il.com>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Ingo Molnar <mingo@...nel.org>,
Kevin Hilman <khilman@...aro.org>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Viresh Kumar <viresh.kumar@...aro.org>
Subject: [PATCH 2/5] irq_work: Force non-lazy works on IPI
As we plan to handle the full nohz IPI using irq work, we need to
enforce non-lazy works outside the tick because it's called under
hrtimer lock. This is not desired from the nohz callback revaluating the
tick because it can take hrtimer lock itself.
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Kevin Hilman <khilman@...aro.org>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Viresh Kumar <viresh.kumar@...aro.org>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
include/linux/irq_work.h | 1 +
kernel/irq_work.c | 58 ++++++++++++++++++++++++++----------------------
kernel/timer.c | 2 +-
3 files changed, 34 insertions(+), 27 deletions(-)
diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h
index 19ae05d..429b1ba 100644
--- a/include/linux/irq_work.h
+++ b/include/linux/irq_work.h
@@ -34,6 +34,7 @@ void init_irq_work(struct irq_work *work, void (*func)(struct irq_work *))
bool irq_work_queue(struct irq_work *work);
void irq_work_run(void);
+void irq_work_run_tick(void);
void irq_work_sync(struct irq_work *work);
#ifdef CONFIG_IRQ_WORK
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 2559383..0a554a6 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -19,8 +19,8 @@
#include <asm/processor.h>
-static DEFINE_PER_CPU(struct llist_head, irq_work_list);
-static DEFINE_PER_CPU(int, irq_work_raised);
+static DEFINE_PER_CPU(struct llist_head, lazy_list);
+static DEFINE_PER_CPU(struct llist_head, raised_list);
/*
* Claim the entry so that no one else will poke at it.
@@ -63,14 +63,14 @@ void __weak arch_irq_work_raise(int cpu)
*/
bool irq_work_queue(struct irq_work *work)
{
+ unsigned long flags;
+
/* Only queue if not already pending */
if (!irq_work_claim(work))
return false;
/* Queue the entry and raise the IPI if needed. */
- preempt_disable();
-
- llist_add(&work->llnode, &__get_cpu_var(irq_work_list));
+ local_irq_save(flags);
/*
* If the work is not "lazy" or the tick is stopped, raise the irq
@@ -78,11 +78,13 @@ bool irq_work_queue(struct irq_work *work)
* for the next tick.
*/
if (!(work->flags & IRQ_WORK_LAZY) || tick_nohz_tick_stopped()) {
- if (!this_cpu_cmpxchg(irq_work_raised, 0, 1))
+ if (llist_add(&work->llnode, &__get_cpu_var(raised_list)))
arch_irq_work_raise(smp_processor_id());
+ } else {
+ llist_add(&work->llnode, &__get_cpu_var(lazy_list));
}
- preempt_enable();
+ local_irq_restore(flags);
return true;
}
@@ -90,10 +92,7 @@ EXPORT_SYMBOL_GPL(irq_work_queue);
bool irq_work_needs_cpu(void)
{
- struct llist_head *this_list;
-
- this_list = &__get_cpu_var(irq_work_list);
- if (llist_empty(this_list))
+ if (llist_empty(&__get_cpu_var(lazy_list)))
return false;
/* All work should have been flushed before going offline */
@@ -102,28 +101,18 @@ bool irq_work_needs_cpu(void)
return true;
}
-static void __irq_work_run(void)
+static void __irq_work_run(struct llist_head *list)
{
unsigned long flags;
struct irq_work *work;
- struct llist_head *this_list;
struct llist_node *llnode;
-
- /*
- * Reset the "raised" state right before we check the list because
- * an NMI may enqueue after we find the list empty from the runner.
- */
- __this_cpu_write(irq_work_raised, 0);
- barrier();
-
- this_list = &__get_cpu_var(irq_work_list);
- if (llist_empty(this_list))
+ if (llist_empty(list))
return;
BUG_ON(!irqs_disabled());
- llnode = llist_del_all(this_list);
+ llnode = llist_del_all(list);
while (llnode != NULL) {
work = llist_entry(llnode, struct irq_work, llnode);
@@ -155,11 +144,27 @@ static void __irq_work_run(void)
void irq_work_run(void)
{
BUG_ON(!in_irq());
- __irq_work_run();
+ __irq_work_run(&__get_cpu_var(raised_list));
+ __irq_work_run(&__get_cpu_var(lazy_list));
}
EXPORT_SYMBOL_GPL(irq_work_run);
/*
+ * Run the lazy irq_work entries on this cpu from the tick. But let
+ * the IPI handle the others. Some works may require to work outside
+ * the tick due to its locking dependencies (hrtimer lock).
+ */
+void irq_work_run_tick(void)
+{
+ BUG_ON(!in_irq());
+#ifndef CONFIG_HAVE_IRQ_WORK_IPI
+ /* No IPI support, we don't have the choice... */
+ __irq_work_run(&__get_cpu_var(raised_list));
+#endif
+ __irq_work_run(&__get_cpu_var(lazy_list));
+}
+
+/*
* Synchronize against the irq_work @entry, ensures the entry is not
* currently in use.
*/
@@ -183,7 +188,8 @@ static int irq_work_cpu_notify(struct notifier_block *self,
/* Called from stop_machine */
if (WARN_ON_ONCE(cpu != smp_processor_id()))
break;
- __irq_work_run();
+ __irq_work_run(&__get_cpu_var(raised_list));
+ __irq_work_run(&__get_cpu_var(lazy_list));
break;
default:
break;
diff --git a/kernel/timer.c b/kernel/timer.c
index 3bb01a3..0251dfa 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1384,7 +1384,7 @@ void update_process_times(int user_tick)
rcu_check_callbacks(cpu, user_tick);
#ifdef CONFIG_IRQ_WORK
if (in_irq())
- irq_work_run();
+ irq_work_run_tick();
#endif
scheduler_tick();
run_posix_cpu_timers(p);
--
1.8.3.1
--
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