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Subject[patch 26/46] hrtimers; add state tracking
From: Thomas Gleixner <tglx@linutronix.de>

Reintroduce ktimers feature "optimized away" by the ktimers review
process: multiple hrtimer states to enable the running of hrtimers
without holding the cpu-base-lock.

(The "optimized" rbtree hack carried only 2 states worth of information
and we need 4 for high resolution timers and dynamic ticks.)

No functional changes.

Build-fixes-from: Andrew Morton <akpm@osdl.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
include/linux/hrtimer.h | 36 +++++++++++++++++++++++++++++++++++-
kernel/hrtimer.c | 40 ++++++++++++++++++++++++++++++++--------
2 files changed, 67 insertions(+), 9 deletions(-)
Index: linux-2.6.20-rc4-mm1-bo/include/linux/hrtimer.h
===================================================================
--- linux-2.6.20-rc4-mm1-bo.orig/include/linux/hrtimer.h
+++ linux-2.6.20-rc4-mm1-bo/include/linux/hrtimer.h
@@ -40,6 +40,34 @@ enum hrtimer_restart {
HRTIMER_RESTART, /* Timer must be restarted */
};

+/*
+ * Bit values to track state of the timer
+ *
+ * Possible states:
+ *
+ * 0x00 inactive
+ * 0x01 enqueued into rbtree
+ * 0x02 callback function running
+ * 0x03 callback function running and enqueued
+ * (was requeued on another CPU)
+ *
+ * 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
+ * and reacquiring the base lock of the hrtimer, another CPU can deliver the
+ * signal and rearm the timer. We have to preserve the callback running state,
+ * as otherwise the timer could be removed before the softirq code finishes the
+ * the handling of the timer.
+ *
+ * The HRTIMER_STATE_ENQUEUE bit is always or'ed to the current state to
+ * preserve the HRTIMER_STATE_CALLBACK bit in the above scenario.
+ *
+ * All state transitions are protected by cpu_base->lock.
+ */
+#define HRTIMER_STATE_INACTIVE 0x00
+#define HRTIMER_STATE_ENQUEUED 0x01
+#define HRTIMER_STATE_CALLBACK 0x02
+
/**
* struct hrtimer - the basic hrtimer structure
* @node: red black tree node for time ordered insertion
@@ -48,6 +76,7 @@ enum hrtimer_restart {
* which the timer is based.
* @function: timer expiry callback function
* @base: pointer to the timer base (per cpu and per clock)
+ * @state: state information (See bit values above)
*
* The hrtimer structure must be initialized by init_hrtimer_#CLOCKTYPE()
*/
@@ -56,6 +85,7 @@ struct hrtimer {
ktime_t expires;
enum hrtimer_restart (*function)(struct hrtimer *);
struct hrtimer_clock_base *base;
+ unsigned long state;
};

/**
@@ -141,9 +171,13 @@ extern int hrtimer_get_res(const clockid
extern ktime_t hrtimer_get_next_event(void);
#endif

+/*
+ * A timer is active, when it is enqueued into the rbtree or the callback
+ * function is running.
+ */
static inline int hrtimer_active(const struct hrtimer *timer)
{
- return rb_parent(&timer->node) != &timer->node;
+ return timer->state != HRTIMER_STATE_INACTIVE;
}

/* Forward a hrtimer so it expires after now: */
Index: linux-2.6.20-rc4-mm1-bo/kernel/hrtimer.c
===================================================================
--- linux-2.6.20-rc4-mm1-bo.orig/kernel/hrtimer.c
+++ linux-2.6.20-rc4-mm1-bo/kernel/hrtimer.c
@@ -150,6 +150,23 @@ static void hrtimer_get_softirq_time(str
}

/*
+ * Helper function to check, whether the timer is on one of the queues
+ */
+static inline int hrtimer_is_queued(struct hrtimer *timer)
+{
+ return timer->state & HRTIMER_STATE_ENQUEUED;
+}
+
+/*
+ * Helper function to check, whether the timer is running the callback
+ * function
+ */
+static inline int hrtimer_callback_running(struct hrtimer *timer)
+{
+ return timer->state & HRTIMER_STATE_CALLBACK;
+}
+
+/*
* Functions and macros which are different for UP/SMP systems are kept in a
* single place
*/
@@ -390,6 +407,11 @@ static void enqueue_hrtimer(struct hrtim
*/
rb_link_node(&timer->node, parent, link);
rb_insert_color(&timer->node, &base->active);
+ /*
+ * HRTIMER_STATE_ENQUEUED is or'ed to the current state to preserve the
+ * state of a possibly running callback.
+ */
+ timer->state |= HRTIMER_STATE_ENQUEUED;

if (!base->first || timer->expires.tv64 <
rb_entry(base->first, struct hrtimer, node)->expires.tv64)
@@ -402,7 +424,8 @@ static void enqueue_hrtimer(struct hrtim
* Caller must hold the base lock.
*/
static void __remove_hrtimer(struct hrtimer *timer,
- struct hrtimer_clock_base *base)
+ struct hrtimer_clock_base *base,
+ unsigned long newstate)
{
/*
* Remove the timer from the rbtree and replace the
@@ -411,7 +434,7 @@ static void __remove_hrtimer(struct hrti
if (base->first == &timer->node)
base->first = rb_next(&timer->node);
rb_erase(&timer->node, &base->active);
- rb_set_parent(&timer->node, &timer->node);
+ timer->state = newstate;
}

/*
@@ -420,8 +443,8 @@ static void __remove_hrtimer(struct hrti
static inline int
remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base)
{
- if (hrtimer_active(timer)) {
- __remove_hrtimer(timer, base);
+ if (hrtimer_is_queued(timer)) {
+ __remove_hrtimer(timer, base, HRTIMER_STATE_INACTIVE);
return 1;
}
return 0;
@@ -493,7 +516,7 @@ int hrtimer_try_to_cancel(struct hrtimer

base = lock_hrtimer_base(timer, &flags);

- if (base->cpu_base->curr_timer != timer)
+ if (!hrtimer_callback_running(timer))
ret = remove_hrtimer(timer, base);

unlock_hrtimer_base(timer, &flags);
@@ -598,7 +621,6 @@ void hrtimer_init(struct hrtimer *timer,
clock_id = CLOCK_MONOTONIC;

timer->base = &cpu_base->clock_base[clock_id];
- rb_set_parent(&timer->node, &timer->node);
}
EXPORT_SYMBOL_GPL(hrtimer_init);

@@ -649,13 +671,14 @@ static inline void run_hrtimer_queue(str

fn = timer->function;
set_curr_timer(cpu_base, timer);
- __remove_hrtimer(timer, base);
+ __remove_hrtimer(timer, base, HRTIMER_STATE_CALLBACK);
spin_unlock_irq(&cpu_base->lock);

restart = fn(timer);

spin_lock_irq(&cpu_base->lock);

+ timer->state &= ~HRTIMER_STATE_CALLBACK;
if (restart != HRTIMER_NORESTART) {
BUG_ON(hrtimer_active(timer));
enqueue_hrtimer(timer, base);
@@ -826,7 +849,8 @@ static void migrate_hrtimer_list(struct

while ((node = rb_first(&old_base->active))) {
timer = rb_entry(node, struct hrtimer, node);
- __remove_hrtimer(timer, old_base);
+ BUG_ON(timer->state & HRTIMER_STATE_CALLBACK);
+ __remove_hrtimer(timer, old_base, HRTIMER_STATE_INACTIVE);
timer->base = new_base;
enqueue_hrtimer(timer, new_base);
}
--

-
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