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Subject[PATCH RFC tip/core/rcu 19/28] nohz: Allow rcu extended quiescent state handling seperately from tick stop
Date
From: Frederic Weisbecker <fweisbec@gmail.com>

It is assumed that rcu won't be used once we switch to tickless
mode and until we restart the tick. However this is not always
true, as in x86-64 where we dereference the idle notifiers after
the tick is stopped.

To prepare for fixing this, add two new APIs:
tick_nohz_idle_enter_norcu() and tick_nohz_idle_exit_norcu().

If no use of RCU is made in the idle loop between
tick_nohz_enter_idle() and tick_nohz_exit_idle() calls, the arch
must instead call the new *_norcu() version such that the arch doesn't
need to call rcu_idle_enter() and rcu_idle_exit().

Otherwise the arch must call tick_nohz_enter_idle() and
tick_nohz_exit_idle() and also call explicitly:

- rcu_idle_enter() after its last use of RCU before the CPU is put
to sleep.
- rcu_idle_exit() before the first use of RCU after the CPU is woken
up.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Cc: David Miller <davem@davemloft.net>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
arch/arm/kernel/process.c | 4 +-
arch/avr32/kernel/process.c | 4 +-
arch/blackfin/kernel/process.c | 4 +-
arch/microblaze/kernel/process.c | 4 +-
arch/mips/kernel/process.c | 4 +-
arch/openrisc/kernel/idle.c | 4 +-
arch/powerpc/kernel/idle.c | 4 +-
arch/powerpc/platforms/iseries/setup.c | 8 +++---
arch/s390/kernel/process.c | 4 +-
arch/sh/kernel/idle.c | 4 +-
arch/sparc/kernel/process_64.c | 4 +-
arch/tile/kernel/process.c | 4 +-
arch/um/kernel/process.c | 4 +-
arch/unicore32/kernel/process.c | 4 +-
arch/x86/kernel/process_32.c | 4 +-
arch/x86/kernel/process_64.c | 4 +-
include/linux/tick.h | 46 +++++++++++++++++++++++++++++--
kernel/time/tick-sched.c | 25 +++++++++--------
18 files changed, 90 insertions(+), 49 deletions(-)
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index f9261d0..4f83362 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -183,7 +183,7 @@ void cpu_idle(void)

/* endless idle loop with no priority at all */
while (1) {
- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();
leds_event(led_idle_start);
while (!need_resched()) {
#ifdef CONFIG_HOTPLUG_CPU
@@ -210,7 +210,7 @@ void cpu_idle(void)
}
}
leds_event(led_idle_end);
- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();
preempt_enable_no_resched();
schedule();
preempt_disable();
diff --git a/arch/avr32/kernel/process.c b/arch/avr32/kernel/process.c
index 6ee7952..34c8c70 100644
--- a/arch/avr32/kernel/process.c
+++ b/arch/avr32/kernel/process.c
@@ -34,10 +34,10 @@ void cpu_idle(void)
{
/* endless idle loop with no priority at all */
while (1) {
- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();
while (!need_resched())
cpu_idle_sleep();
- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();
preempt_enable_no_resched();
schedule();
preempt_disable();
diff --git a/arch/blackfin/kernel/process.c b/arch/blackfin/kernel/process.c
index 7b141b5..57e0749 100644
--- a/arch/blackfin/kernel/process.c
+++ b/arch/blackfin/kernel/process.c
@@ -88,10 +88,10 @@ void cpu_idle(void)
#endif
if (!idle)
idle = default_idle;
- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();
while (!need_resched())
idle();
- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();
preempt_enable_no_resched();
schedule();
preempt_disable();
diff --git a/arch/microblaze/kernel/process.c b/arch/microblaze/kernel/process.c
index 6dc123e..c6ece38 100644
--- a/arch/microblaze/kernel/process.c
+++ b/arch/microblaze/kernel/process.c
@@ -103,10 +103,10 @@ void cpu_idle(void)
if (!idle)
idle = default_idle;

- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();
while (!need_resched())
idle();
- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();

preempt_enable_no_resched();
schedule();
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index d50a005..7df2ffc 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -56,7 +56,7 @@ void __noreturn cpu_idle(void)

/* endless idle loop with no priority at all */
while (1) {
- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();
while (!need_resched() && cpu_online(cpu)) {
#ifdef CONFIG_MIPS_MT_SMTC
extern void smtc_idle_loop_hook(void);
@@ -77,7 +77,7 @@ void __noreturn cpu_idle(void)
system_state == SYSTEM_BOOTING))
play_dead();
#endif
- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();
preempt_enable_no_resched();
schedule();
preempt_disable();
diff --git a/arch/openrisc/kernel/idle.c b/arch/openrisc/kernel/idle.c
index fb6a9bf..2e82cd0 100644
--- a/arch/openrisc/kernel/idle.c
+++ b/arch/openrisc/kernel/idle.c
@@ -51,7 +51,7 @@ void cpu_idle(void)

/* endless idle loop with no priority at all */
while (1) {
- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();

while (!need_resched()) {
check_pgt_cache();
@@ -69,7 +69,7 @@ void cpu_idle(void)
set_thread_flag(TIF_POLLING_NRFLAG);
}

- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();
preempt_enable_no_resched();
schedule();
preempt_disable();
diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c
index 878572f..2e782a3 100644
--- a/arch/powerpc/kernel/idle.c
+++ b/arch/powerpc/kernel/idle.c
@@ -56,7 +56,7 @@ void cpu_idle(void)

set_thread_flag(TIF_POLLING_NRFLAG);
while (1) {
- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();
while (!need_resched() && !cpu_should_die()) {
ppc64_runlatch_off();

@@ -93,7 +93,7 @@ void cpu_idle(void)

HMT_medium();
ppc64_runlatch_on();
- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();
preempt_enable_no_resched();
if (cpu_should_die())
cpu_die();
diff --git a/arch/powerpc/platforms/iseries/setup.c b/arch/powerpc/platforms/iseries/setup.c
index e2f5fad..77ff6eb 100644
--- a/arch/powerpc/platforms/iseries/setup.c
+++ b/arch/powerpc/platforms/iseries/setup.c
@@ -562,7 +562,7 @@ static void yield_shared_processor(void)
static void iseries_shared_idle(void)
{
while (1) {
- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();
while (!need_resched() && !hvlpevent_is_pending()) {
local_irq_disable();
ppc64_runlatch_off();
@@ -576,7 +576,7 @@ static void iseries_shared_idle(void)
}

ppc64_runlatch_on();
- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();

if (hvlpevent_is_pending())
process_iSeries_events();
@@ -592,7 +592,7 @@ static void iseries_dedicated_idle(void)
set_thread_flag(TIF_POLLING_NRFLAG);

while (1) {
- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();
if (!need_resched()) {
while (!need_resched()) {
ppc64_runlatch_off();
@@ -609,7 +609,7 @@ static void iseries_dedicated_idle(void)
}

ppc64_runlatch_on();
- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();
preempt_enable_no_resched();
schedule();
preempt_disable();
diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index db3e930..44028ae 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -90,10 +90,10 @@ static void default_idle(void)
void cpu_idle(void)
{
for (;;) {
- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();
while (!need_resched())
default_idle();
- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();
preempt_enable_no_resched();
schedule();
preempt_disable();
diff --git a/arch/sh/kernel/idle.c b/arch/sh/kernel/idle.c
index 6015743..ad58e75 100644
--- a/arch/sh/kernel/idle.c
+++ b/arch/sh/kernel/idle.c
@@ -89,7 +89,7 @@ void cpu_idle(void)

/* endless idle loop with no priority at all */
while (1) {
- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();

while (!need_resched()) {
check_pgt_cache();
@@ -111,7 +111,7 @@ void cpu_idle(void)
start_critical_timings();
}

- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();
preempt_enable_no_resched();
schedule();
preempt_disable();
diff --git a/arch/sparc/kernel/process_64.c b/arch/sparc/kernel/process_64.c
index 1235f63..78b1bc0 100644
--- a/arch/sparc/kernel/process_64.c
+++ b/arch/sparc/kernel/process_64.c
@@ -95,12 +95,12 @@ void cpu_idle(void)
set_thread_flag(TIF_POLLING_NRFLAG);

while(1) {
- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();

while (!need_resched() && !cpu_is_offline(cpu))
sparc64_yield(cpu);

- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();

preempt_enable_no_resched();

diff --git a/arch/tile/kernel/process.c b/arch/tile/kernel/process.c
index 920e674..53ac895 100644
--- a/arch/tile/kernel/process.c
+++ b/arch/tile/kernel/process.c
@@ -85,7 +85,7 @@ void cpu_idle(void)

/* endless idle loop with no priority at all */
while (1) {
- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();
while (!need_resched()) {
if (cpu_is_offline(cpu))
BUG(); /* no HOTPLUG_CPU */
@@ -105,7 +105,7 @@ void cpu_idle(void)
local_irq_enable();
current_thread_info()->status |= TS_POLLING;
}
- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();
preempt_enable_no_resched();
schedule();
preempt_disable();
diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
index 41acf59..9e7176b 100644
--- a/arch/um/kernel/process.c
+++ b/arch/um/kernel/process.c
@@ -245,10 +245,10 @@ void default_idle(void)
if (need_resched())
schedule();

- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();
nsecs = disable_timer();
idle_sleep(nsecs);
- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();
}
}

diff --git a/arch/unicore32/kernel/process.c b/arch/unicore32/kernel/process.c
index 9999b9a..095ff5a 100644
--- a/arch/unicore32/kernel/process.c
+++ b/arch/unicore32/kernel/process.c
@@ -55,7 +55,7 @@ void cpu_idle(void)
{
/* endless idle loop with no priority at all */
while (1) {
- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();
while (!need_resched()) {
local_irq_disable();
stop_critical_timings();
@@ -63,7 +63,7 @@ void cpu_idle(void)
local_irq_enable();
start_critical_timings();
}
- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();
preempt_enable_no_resched();
schedule();
preempt_disable();
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index ad93205..f311d096 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -98,7 +98,7 @@ void cpu_idle(void)

/* endless idle loop with no priority at all */
while (1) {
- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();
while (!need_resched()) {

check_pgt_cache();
@@ -114,7 +114,7 @@ void cpu_idle(void)
pm_idle();
start_critical_timings();
}
- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();
preempt_enable_no_resched();
schedule();
preempt_disable();
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 9ca714e..e72daf9 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -121,7 +121,7 @@ void cpu_idle(void)

/* endless idle loop with no priority at all */
while (1) {
- tick_nohz_idle_enter();
+ tick_nohz_idle_enter_norcu();
while (!need_resched()) {

rmb();
@@ -147,7 +147,7 @@ void cpu_idle(void)
__exit_idle();
}

- tick_nohz_idle_exit();
+ tick_nohz_idle_exit_norcu();
preempt_enable_no_resched();
schedule();
preempt_disable();
diff --git a/include/linux/tick.h b/include/linux/tick.h
index 0df1d50..327434a 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -7,6 +7,7 @@
#define _LINUX_TICK_H

#include <linux/clockchips.h>
+#include <linux/irqflags.h>

#ifdef CONFIG_GENERIC_CLOCKEVENTS

@@ -121,18 +122,57 @@ static inline int tick_oneshot_mode_active(void) { return 0; }
#endif /* !CONFIG_GENERIC_CLOCKEVENTS */

# ifdef CONFIG_NO_HZ
-extern void tick_nohz_idle_enter(void);
+extern void __tick_nohz_idle_enter(void);
+static inline void tick_nohz_idle_enter(void)
+{
+ local_irq_disable();
+ __tick_nohz_idle_enter();
+ local_irq_enable();
+}
extern void tick_nohz_idle_exit(void);
+
+/*
+ * Call this pair of function if the arch doesn't make any use
+ * of RCU in-between. You won't need to call rcu_idle_enter() and
+ * rcu_idle_exit().
+ * Otherwise you need to call tick_nohz_idle_enter() and tick_nohz_idle_exit()
+ * and explicitly tell RCU about the window around the place the CPU enters low
+ * power mode where no RCU use is made. This is done by calling rcu_idle_enter()
+ * after the last use of RCU before the CPU is put to sleep and by calling
+ * rcu_idle_exit() before the first use of RCU after the CPU woke up.
+ */
+static inline void tick_nohz_idle_enter_norcu(void)
+{
+ /*
+ * Also call rcu_idle_enter() in the irq disabled section even
+ * if it disables irq itself.
+ * Just an optimization that prevents from an interrupt happening
+ * between it and __tick_nohz_idle_enter() to lose time to help
+ * completing a grace period while we could be in extended grace
+ * period already.
+ */
+ local_irq_disable();
+ __tick_nohz_idle_enter();
+ rcu_idle_enter();
+ local_irq_enable();
+}
+static inline void tick_nohz_idle_exit_norcu(void)
+{
+ rcu_idle_exit();
+ tick_nohz_idle_exit();
+}
extern void tick_nohz_irq_exit(void);
extern ktime_t tick_nohz_get_sleep_length(void);
extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time);
extern u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time);
# else
-static inline void tick_nohz_idle_enter(void)
+static inline void tick_nohz_idle_enter(void) { }
+static inline void tick_nohz_idle_exit(void) { }
+static inline void tick_nohz_idle_enter_norcu(void)
{
rcu_idle_enter();
}
-static inline void tick_nohz_idle_exit(void)
+static inline void tick_nohz_idle_exit_norcu(void)
{
rcu_idle_exit();
}
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 52b7ace..360d028 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -424,18 +424,22 @@ out:
*
* When the next event is more than a tick into the future, stop the idle tick
* Called when we start the idle loop.
- * This also enters into RCU extended quiescent state so that this CPU doesn't
- * need anymore to be part of any global grace period completion. This way
- * the tick can be stopped safely as we don't need to report quiescent states.
+ *
+ * If no use of RCU is made in the idle loop between
+ * tick_nohz_idle_enter() and tick_nohz_idle_exit() calls, then
+ * tick_nohz_idle_enter_norcu() should be called instead and the arch
+ * doesn't need to call rcu_idle_enter() and rcu_idle_exit() explicitly.
+ *
+ * Otherwise the arch is responsible of calling:
+ *
+ * - rcu_idle_enter() after its last use of RCU before the CPU is put
+ * to sleep.
+ * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
*/
-void tick_nohz_idle_enter(void)
+void __tick_nohz_idle_enter(void)
{
struct tick_sched *ts;

- WARN_ON_ONCE(irqs_disabled());
-
- local_irq_disable();
-
ts = &__get_cpu_var(tick_cpu_sched);
/*
* set ts->inidle unconditionally. even if the system did not
@@ -444,9 +448,6 @@ void tick_nohz_idle_enter(void)
*/
ts->inidle = 1;
tick_nohz_stop_sched_tick(ts);
- rcu_idle_enter();
-
- local_irq_enable();
}

/**
@@ -522,7 +523,7 @@ void tick_nohz_idle_exit(void)
ktime_t now;

local_irq_disable();
- rcu_idle_exit();
+
if (ts->idle_active || (ts->inidle && ts->tick_stopped))
now = ktime_get();

--
1.7.3.2


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