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Date: Tue, 30 Sep 2008 17:16:43 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Andrew Morton <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [GIT pull] timer fixes for .27
* Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> On Tue, 30 Sep 2008, Thomas Gleixner wrote:
> >
> > Please pull the latest timers-fixes-for-linus git tree from:
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git timers-fixes-for-linus
>
> Did you forget to push? The tip of that branch is still commit
> 1eda81495a49a4ee91d8863b0a441a624375efea ("x86: prevent stale state of
> c1e_mask ...") which I already pulled last week.
hm, i just re-ran the pushout script - see below.
Ingo
--------->
Linus,
Please pull the latest timers-fixes-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git timers-fixes-for-linus
Thanks,
Ingo
------------------>
Thomas Gleixner (4):
hrtimer: migrate pending list on cpu offline
hrtimer: fix migration of CB_IRQSAFE_NO_SOFTIRQ hrtimers
hrtimer: mark migration state
hrtimer: prevent migration of per CPU hrtimers
include/linux/hrtimer.h | 18 ++++++--
kernel/hrtimer.c | 95 +++++++++++++++++++++++++++++++++++++----
kernel/sched.c | 4 +-
kernel/time/tick-sched.c | 2 +-
kernel/trace/trace_sysprof.c | 2 +-
5 files changed, 103 insertions(+), 18 deletions(-)
diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 6d93dce..2f245fe 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -47,14 +47,22 @@ enum hrtimer_restart {
* HRTIMER_CB_IRQSAFE: Callback may run in hardirq context
* HRTIMER_CB_IRQSAFE_NO_RESTART: Callback may run in hardirq context and
* does not restart the timer
- * HRTIMER_CB_IRQSAFE_NO_SOFTIRQ: Callback must run in hardirq context
- * Special mode for tick emultation
+ * HRTIMER_CB_IRQSAFE_PERCPU: Callback must run in hardirq context
+ * Special mode for tick emulation and
+ * scheduler timer. Such timers are per
+ * cpu and not allowed to be migrated on
+ * cpu unplug.
+ * HRTIMER_CB_IRQSAFE_UNLOCKED: Callback should run in hardirq context
+ * with timer->base lock unlocked
+ * used for timers which call wakeup to
+ * avoid lock order problems with rq->lock
*/
enum hrtimer_cb_mode {
HRTIMER_CB_SOFTIRQ,
HRTIMER_CB_IRQSAFE,
HRTIMER_CB_IRQSAFE_NO_RESTART,
- HRTIMER_CB_IRQSAFE_NO_SOFTIRQ,
+ HRTIMER_CB_IRQSAFE_PERCPU,
+ HRTIMER_CB_IRQSAFE_UNLOCKED,
};
/*
@@ -67,9 +75,10 @@ enum hrtimer_cb_mode {
* 0x02 callback function running
* 0x04 callback pending (high resolution mode)
*
- * Special case:
+ * Special cases:
* 0x03 callback function running and enqueued
* (was requeued on another CPU)
+ * 0x09 timer was migrated on CPU hotunplug
* The "callback function running and enqueued" status is only possible on
* SMP. It happens for example when a posix timer expired and the callback
* queued a signal. Between dropping the lock which protects the posix timer
@@ -87,6 +96,7 @@ enum hrtimer_cb_mode {
#define HRTIMER_STATE_ENQUEUED 0x01
#define HRTIMER_STATE_CALLBACK 0x02
#define HRTIMER_STATE_PENDING 0x04
+#define HRTIMER_STATE_MIGRATE 0x08
/**
* struct hrtimer - the basic hrtimer structure
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index b8e4dce..cdec83e 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -672,13 +672,14 @@ static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer,
*/
BUG_ON(timer->function(timer) != HRTIMER_NORESTART);
return 1;
- case HRTIMER_CB_IRQSAFE_NO_SOFTIRQ:
+ case HRTIMER_CB_IRQSAFE_PERCPU:
+ case HRTIMER_CB_IRQSAFE_UNLOCKED:
/*
* This is solely for the sched tick emulation with
* dynamic tick support to ensure that we do not
* restart the tick right on the edge and end up with
* the tick timer in the softirq ! The calling site
- * takes care of this.
+ * takes care of this. Also used for hrtimer sleeper !
*/
debug_hrtimer_deactivate(timer);
return 1;
@@ -1245,7 +1246,8 @@ static void __run_hrtimer(struct hrtimer *timer)
timer_stats_account_hrtimer(timer);
fn = timer->function;
- if (timer->cb_mode == HRTIMER_CB_IRQSAFE_NO_SOFTIRQ) {
+ if (timer->cb_mode == HRTIMER_CB_IRQSAFE_PERCPU ||
+ timer->cb_mode == HRTIMER_CB_IRQSAFE_UNLOCKED) {
/*
* Used for scheduler timers, avoid lock inversion with
* rq->lock and tasklist_lock.
@@ -1452,7 +1454,7 @@ void hrtimer_init_sleeper(struct hrtimer_sleeper *sl, struct task_struct *task)
sl->timer.function = hrtimer_wakeup;
sl->task = task;
#ifdef CONFIG_HIGH_RES_TIMERS
- sl->timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
+ sl->timer.cb_mode = HRTIMER_CB_IRQSAFE_UNLOCKED;
#endif
}
@@ -1591,29 +1593,95 @@ static void __cpuinit init_hrtimers_cpu(int cpu)
#ifdef CONFIG_HOTPLUG_CPU
-static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
- struct hrtimer_clock_base *new_base)
+static int migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
+ struct hrtimer_clock_base *new_base, int dcpu)
{
struct hrtimer *timer;
struct rb_node *node;
+ int raise = 0;
while ((node = rb_first(&old_base->active))) {
timer = rb_entry(node, struct hrtimer, node);
BUG_ON(hrtimer_callback_running(timer));
debug_hrtimer_deactivate(timer);
- __remove_hrtimer(timer, old_base, HRTIMER_STATE_INACTIVE, 0);
+
+ /*
+ * Should not happen. Per CPU timers should be
+ * canceled _before_ the migration code is called
+ */
+ if (timer->cb_mode == HRTIMER_CB_IRQSAFE_PERCPU) {
+ __remove_hrtimer(timer, old_base,
+ HRTIMER_STATE_INACTIVE, 0);
+ WARN(1, "hrtimer (%p %p)active but cpu %d dead\n",
+ timer, timer->function, dcpu);
+ continue;
+ }
+
+ /*
+ * Mark it as STATE_MIGRATE not INACTIVE otherwise the
+ * timer could be seen as !active and just vanish away
+ * under us on another CPU
+ */
+ __remove_hrtimer(timer, old_base, HRTIMER_STATE_MIGRATE, 0);
timer->base = new_base;
/*
* Enqueue the timer. Allow reprogramming of the event device
*/
enqueue_hrtimer(timer, new_base, 1);
+
+#ifdef CONFIG_HIGH_RES_TIMERS
+ /*
+ * Happens with high res enabled when the timer was
+ * already expired and the callback mode is
+ * HRTIMER_CB_IRQSAFE_UNLOCKED (hrtimer_sleeper). The
+ * enqueue code does not move them to the soft irq
+ * pending list for performance/latency reasons, but
+ * in the migration state, we need to do that
+ * otherwise we end up with a stale timer.
+ */
+ if (timer->state == HRTIMER_STATE_MIGRATE) {
+ timer->state = HRTIMER_STATE_PENDING;
+ list_add_tail(&timer->cb_entry,
+ &new_base->cpu_base->cb_pending);
+ raise = 1;
+ }
+#endif
+ /* Clear the migration state bit */
+ timer->state &= ~HRTIMER_STATE_MIGRATE;
+ }
+ return raise;
+}
+
+#ifdef CONFIG_HIGH_RES_TIMERS
+static int migrate_hrtimer_pending(struct hrtimer_cpu_base *old_base,
+ struct hrtimer_cpu_base *new_base)
+{
+ struct hrtimer *timer;
+ int raise = 0;
+
+ while (!list_empty(&old_base->cb_pending)) {
+ timer = list_entry(old_base->cb_pending.next,
+ struct hrtimer, cb_entry);
+
+ __remove_hrtimer(timer, timer->base, HRTIMER_STATE_PENDING, 0);
+ timer->base = &new_base->clock_base[timer->base->index];
+ list_add_tail(&timer->cb_entry, &new_base->cb_pending);
+ raise = 1;
}
+ return raise;
+}
+#else
+static int migrate_hrtimer_pending(struct hrtimer_cpu_base *old_base,
+ struct hrtimer_cpu_base *new_base)
+{
+ return 0;
}
+#endif
static void migrate_hrtimers(int cpu)
{
struct hrtimer_cpu_base *old_base, *new_base;
- int i;
+ int i, raise = 0;
BUG_ON(cpu_online(cpu));
old_base = &per_cpu(hrtimer_bases, cpu);
@@ -1626,14 +1694,21 @@ static void migrate_hrtimers(int cpu)
spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);
for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
- migrate_hrtimer_list(&old_base->clock_base[i],
- &new_base->clock_base[i]);
+ if (migrate_hrtimer_list(&old_base->clock_base[i],
+ &new_base->clock_base[i], cpu))
+ raise = 1;
}
+ if (migrate_hrtimer_pending(old_base, new_base))
+ raise = 1;
+
spin_unlock(&old_base->lock);
spin_unlock(&new_base->lock);
local_irq_enable();
put_cpu_var(hrtimer_bases);
+
+ if (raise)
+ hrtimer_raise_softirq();
}
#endif /* CONFIG_HOTPLUG_CPU */
diff --git a/kernel/sched.c b/kernel/sched.c
index 13dd2db..ad1962d 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -201,7 +201,7 @@ void init_rt_bandwidth(struct rt_bandwidth *rt_b, u64 period, u64 runtime)
hrtimer_init(&rt_b->rt_period_timer,
CLOCK_MONOTONIC, HRTIMER_MODE_REL);
rt_b->rt_period_timer.function = sched_rt_period_timer;
- rt_b->rt_period_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
+ rt_b->rt_period_timer.cb_mode = HRTIMER_CB_IRQSAFE_UNLOCKED;
}
static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
@@ -1119,7 +1119,7 @@ static void init_rq_hrtick(struct rq *rq)
hrtimer_init(&rq->hrtick_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
rq->hrtick_timer.function = hrtick;
- rq->hrtick_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
+ rq->hrtick_timer.cb_mode = HRTIMER_CB_IRQSAFE_PERCPU;
}
#else
static inline void hrtick_clear(struct rq *rq)
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 39019b3..cb02324 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -625,7 +625,7 @@ void tick_setup_sched_timer(void)
*/
hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
ts->sched_timer.function = tick_sched_timer;
- ts->sched_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
+ ts->sched_timer.cb_mode = HRTIMER_CB_IRQSAFE_PERCPU;
/* Get the next period (per cpu) */
ts->sched_timer.expires = tick_init_jiffy_update();
diff --git a/kernel/trace/trace_sysprof.c b/kernel/trace/trace_sysprof.c
index bb948e5..db58fb6 100644
--- a/kernel/trace/trace_sysprof.c
+++ b/kernel/trace/trace_sysprof.c
@@ -202,7 +202,7 @@ static void start_stack_timer(int cpu)
hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
hrtimer->function = stack_trace_timer_fn;
- hrtimer->cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
+ hrtimer->cb_mode = HRTIMER_CB_IRQSAFE_PERCPU;
hrtimer_start(hrtimer, ns_to_ktime(sample_period), HRTIMER_MODE_REL);
}
--
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