Revision 63cae12bce9861cec309798d34701cf3da20bc71 authored by Peter Zijlstra on 09 December 2016, 13:59:00 UTC, committed by Ingo Molnar on 14 January 2017, 09:56:10 UTC
There is problem with installing an event in a task that is 'stuck' on
an offline CPU.
Blocked tasks are not dis-assosciated from offlined CPUs, after all, a
blocked task doesn't run and doesn't require a CPU etc.. Only on
wakeup do we ammend the situation and place the task on a available
CPU.
If we hit such a task with perf_install_in_context() we'll loop until
either that task wakes up or the CPU comes back online, if the task
waking depends on the event being installed, we're stuck.
While looking into this issue, I also spotted another problem, if we
hit a task with perf_install_in_context() that is in the middle of
being migrated, that is we observe the old CPU before sending the IPI,
but run the IPI (on the old CPU) while the task is already running on
the new CPU, things also go sideways.
Rework things to rely on task_curr() -- outside of rq->lock -- which
is rather tricky. Imagine the following scenario where we're trying to
install the first event into our task 't':
CPU0 CPU1 CPU2
(current == t)
t->perf_event_ctxp[] = ctx;
smp_mb();
cpu = task_cpu(t);
switch(t, n);
migrate(t, 2);
switch(p, t);
ctx = t->perf_event_ctxp[]; // must not be NULL
smp_function_call(cpu, ..);
generic_exec_single()
func();
spin_lock(ctx->lock);
if (task_curr(t)) // false
add_event_to_ctx();
spin_unlock(ctx->lock);
perf_event_context_sched_in();
spin_lock(ctx->lock);
// sees event
So its CPU0's store of t->perf_event_ctxp[] that must not go 'missing'.
Because if CPU2's load of that variable were to observe NULL, it would
not try to schedule the ctx and we'd have a task running without its
counter, which would be 'bad'.
As long as we observe !NULL, we'll acquire ctx->lock. If we acquire it
first and not see the event yet, then CPU0 must observe task_curr()
and retry. If the install happens first, then we must see the event on
sched-in and all is well.
I think we can translate the first part (until the 'must not be NULL')
of the scenario to a litmus test like:
C C-peterz
{
}
P0(int *x, int *y)
{
int r1;
WRITE_ONCE(*x, 1);
smp_mb();
r1 = READ_ONCE(*y);
}
P1(int *y, int *z)
{
WRITE_ONCE(*y, 1);
smp_store_release(z, 1);
}
P2(int *x, int *z)
{
int r1;
int r2;
r1 = smp_load_acquire(z);
smp_mb();
r2 = READ_ONCE(*x);
}
exists
(0:r1=0 /\ 2:r1=1 /\ 2:r2=0)
Where:
x is perf_event_ctxp[],
y is our tasks's CPU, and
z is our task being placed on the rq of CPU2.
The P0 smp_mb() is the one added by this patch, ordering the store to
perf_event_ctxp[] from find_get_context() and the load of task_cpu()
in task_function_call().
The smp_store_release/smp_load_acquire model the RCpc locking of the
rq->lock and the smp_mb() of P2 is the context switch switching from
whatever CPU2 was running to our task 't'.
This litmus test evaluates into:
Test C-peterz Allowed
States 7
0:r1=0; 2:r1=0; 2:r2=0;
0:r1=0; 2:r1=0; 2:r2=1;
0:r1=0; 2:r1=1; 2:r2=1;
0:r1=1; 2:r1=0; 2:r2=0;
0:r1=1; 2:r1=0; 2:r2=1;
0:r1=1; 2:r1=1; 2:r2=0;
0:r1=1; 2:r1=1; 2:r2=1;
No
Witnesses
Positive: 0 Negative: 7
Condition exists (0:r1=0 /\ 2:r1=1 /\ 2:r2=0)
Observation C-peterz Never 0 7
Hash=e427f41d9146b2a5445101d3e2fcaa34
And the strong and weak model agree.
Reported-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Will Deacon <will.deacon@arm.com>
Cc: jeremy.linton@arm.com
Link: http://lkml.kernel.org/r/20161209135900.GU3174@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
1 parent ad5013d
leds-ktd2692.c
/*
* LED driver : leds-ktd2692.c
*
* Copyright (C) 2015 Samsung Electronics
* Ingi Kim <ingi2.kim@samsung.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/delay.h>
#include <linux/err.h>
#include <linux/gpio/consumer.h>
#include <linux/led-class-flash.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/regulator/consumer.h>
/* Value related the movie mode */
#define KTD2692_MOVIE_MODE_CURRENT_LEVELS 16
#define KTD2692_MM_TO_FL_RATIO(x) ((x) / 3)
#define KTD2962_MM_MIN_CURR_THRESHOLD_SCALE 8
/* Value related the flash mode */
#define KTD2692_FLASH_MODE_TIMEOUT_LEVELS 8
#define KTD2692_FLASH_MODE_TIMEOUT_DISABLE 0
#define KTD2692_FLASH_MODE_CURR_PERCENT(x) (((x) * 16) / 100)
/* Macro for getting offset of flash timeout */
#define GET_TIMEOUT_OFFSET(timeout, step) ((timeout) / (step))
/* Base register address */
#define KTD2692_REG_LVP_BASE 0x00
#define KTD2692_REG_FLASH_TIMEOUT_BASE 0x20
#define KTD2692_REG_MM_MIN_CURR_THRESHOLD_BASE 0x40
#define KTD2692_REG_MOVIE_CURRENT_BASE 0x60
#define KTD2692_REG_FLASH_CURRENT_BASE 0x80
#define KTD2692_REG_MODE_BASE 0xA0
/* Set bit coding time for expresswire interface */
#define KTD2692_TIME_RESET_US 700
#define KTD2692_TIME_DATA_START_TIME_US 10
#define KTD2692_TIME_HIGH_END_OF_DATA_US 350
#define KTD2692_TIME_LOW_END_OF_DATA_US 10
#define KTD2692_TIME_SHORT_BITSET_US 4
#define KTD2692_TIME_LONG_BITSET_US 12
/* KTD2692 default length of name */
#define KTD2692_NAME_LENGTH 20
enum ktd2692_bitset {
KTD2692_LOW = 0,
KTD2692_HIGH,
};
/* Movie / Flash Mode Control */
enum ktd2692_led_mode {
KTD2692_MODE_DISABLE = 0, /* default */
KTD2692_MODE_MOVIE,
KTD2692_MODE_FLASH,
};
struct ktd2692_led_config_data {
/* maximum LED current in movie mode */
u32 movie_max_microamp;
/* maximum LED current in flash mode */
u32 flash_max_microamp;
/* maximum flash timeout */
u32 flash_max_timeout;
/* max LED brightness level */
enum led_brightness max_brightness;
};
struct ktd2692_context {
/* Related LED Flash class device */
struct led_classdev_flash fled_cdev;
/* secures access to the device */
struct mutex lock;
struct regulator *regulator;
struct gpio_desc *aux_gpio;
struct gpio_desc *ctrl_gpio;
enum ktd2692_led_mode mode;
enum led_brightness torch_brightness;
};
static struct ktd2692_context *fled_cdev_to_led(
struct led_classdev_flash *fled_cdev)
{
return container_of(fled_cdev, struct ktd2692_context, fled_cdev);
}
static void ktd2692_expresswire_start(struct ktd2692_context *led)
{
gpiod_direction_output(led->ctrl_gpio, KTD2692_HIGH);
udelay(KTD2692_TIME_DATA_START_TIME_US);
}
static void ktd2692_expresswire_reset(struct ktd2692_context *led)
{
gpiod_direction_output(led->ctrl_gpio, KTD2692_LOW);
udelay(KTD2692_TIME_RESET_US);
}
static void ktd2692_expresswire_end(struct ktd2692_context *led)
{
gpiod_direction_output(led->ctrl_gpio, KTD2692_LOW);
udelay(KTD2692_TIME_LOW_END_OF_DATA_US);
gpiod_direction_output(led->ctrl_gpio, KTD2692_HIGH);
udelay(KTD2692_TIME_HIGH_END_OF_DATA_US);
}
static void ktd2692_expresswire_set_bit(struct ktd2692_context *led, bool bit)
{
/*
* The Low Bit(0) and High Bit(1) is based on a time detection
* algorithm between time low and time high
* Time_(L_LB) : Low time of the Low Bit(0)
* Time_(H_LB) : High time of the LOW Bit(0)
* Time_(L_HB) : Low time of the High Bit(1)
* Time_(H_HB) : High time of the High Bit(1)
*
* It can be simplified to:
* Low Bit(0) : 2 * Time_(H_LB) < Time_(L_LB)
* High Bit(1) : 2 * Time_(L_HB) < Time_(H_HB)
* HIGH ___ ____ _.. _________ ___
* |_________| |_.. |____| |__|
* LOW <L_LB> <H_LB> <L_HB> <H_HB>
* [ Low Bit (0) ] [ High Bit(1) ]
*/
if (bit) {
gpiod_direction_output(led->ctrl_gpio, KTD2692_LOW);
udelay(KTD2692_TIME_SHORT_BITSET_US);
gpiod_direction_output(led->ctrl_gpio, KTD2692_HIGH);
udelay(KTD2692_TIME_LONG_BITSET_US);
} else {
gpiod_direction_output(led->ctrl_gpio, KTD2692_LOW);
udelay(KTD2692_TIME_LONG_BITSET_US);
gpiod_direction_output(led->ctrl_gpio, KTD2692_HIGH);
udelay(KTD2692_TIME_SHORT_BITSET_US);
}
}
static void ktd2692_expresswire_write(struct ktd2692_context *led, u8 value)
{
int i;
ktd2692_expresswire_start(led);
for (i = 7; i >= 0; i--)
ktd2692_expresswire_set_bit(led, value & BIT(i));
ktd2692_expresswire_end(led);
}
static int ktd2692_led_brightness_set(struct led_classdev *led_cdev,
enum led_brightness brightness)
{
struct led_classdev_flash *fled_cdev = lcdev_to_flcdev(led_cdev);
struct ktd2692_context *led = fled_cdev_to_led(fled_cdev);
mutex_lock(&led->lock);
if (brightness == LED_OFF) {
led->mode = KTD2692_MODE_DISABLE;
gpiod_direction_output(led->aux_gpio, KTD2692_LOW);
} else {
ktd2692_expresswire_write(led, brightness |
KTD2692_REG_MOVIE_CURRENT_BASE);
led->mode = KTD2692_MODE_MOVIE;
}
ktd2692_expresswire_write(led, led->mode | KTD2692_REG_MODE_BASE);
mutex_unlock(&led->lock);
return 0;
}
static int ktd2692_led_flash_strobe_set(struct led_classdev_flash *fled_cdev,
bool state)
{
struct ktd2692_context *led = fled_cdev_to_led(fled_cdev);
struct led_flash_setting *timeout = &fled_cdev->timeout;
u32 flash_tm_reg;
mutex_lock(&led->lock);
if (state) {
flash_tm_reg = GET_TIMEOUT_OFFSET(timeout->val, timeout->step);
ktd2692_expresswire_write(led, flash_tm_reg
| KTD2692_REG_FLASH_TIMEOUT_BASE);
led->mode = KTD2692_MODE_FLASH;
gpiod_direction_output(led->aux_gpio, KTD2692_HIGH);
} else {
led->mode = KTD2692_MODE_DISABLE;
gpiod_direction_output(led->aux_gpio, KTD2692_LOW);
}
ktd2692_expresswire_write(led, led->mode | KTD2692_REG_MODE_BASE);
fled_cdev->led_cdev.brightness = LED_OFF;
led->mode = KTD2692_MODE_DISABLE;
mutex_unlock(&led->lock);
return 0;
}
static int ktd2692_led_flash_timeout_set(struct led_classdev_flash *fled_cdev,
u32 timeout)
{
return 0;
}
static void ktd2692_init_movie_current_max(struct ktd2692_led_config_data *cfg)
{
u32 offset, step;
u32 movie_current_microamp;
offset = KTD2692_MOVIE_MODE_CURRENT_LEVELS;
step = KTD2692_MM_TO_FL_RATIO(cfg->flash_max_microamp)
/ KTD2692_MOVIE_MODE_CURRENT_LEVELS;
do {
movie_current_microamp = step * offset;
offset--;
} while ((movie_current_microamp > cfg->movie_max_microamp) &&
(offset > 0));
cfg->max_brightness = offset;
}
static void ktd2692_init_flash_timeout(struct led_classdev_flash *fled_cdev,
struct ktd2692_led_config_data *cfg)
{
struct led_flash_setting *setting;
setting = &fled_cdev->timeout;
setting->min = KTD2692_FLASH_MODE_TIMEOUT_DISABLE;
setting->max = cfg->flash_max_timeout;
setting->step = cfg->flash_max_timeout
/ (KTD2692_FLASH_MODE_TIMEOUT_LEVELS - 1);
setting->val = cfg->flash_max_timeout;
}
static void ktd2692_setup(struct ktd2692_context *led)
{
led->mode = KTD2692_MODE_DISABLE;
ktd2692_expresswire_reset(led);
gpiod_direction_output(led->aux_gpio, KTD2692_LOW);
ktd2692_expresswire_write(led, (KTD2962_MM_MIN_CURR_THRESHOLD_SCALE - 1)
| KTD2692_REG_MM_MIN_CURR_THRESHOLD_BASE);
ktd2692_expresswire_write(led, KTD2692_FLASH_MODE_CURR_PERCENT(45)
| KTD2692_REG_FLASH_CURRENT_BASE);
}
static int ktd2692_parse_dt(struct ktd2692_context *led, struct device *dev,
struct ktd2692_led_config_data *cfg)
{
struct device_node *np = dev->of_node;
struct device_node *child_node;
int ret;
if (!dev->of_node)
return -ENXIO;
led->ctrl_gpio = devm_gpiod_get(dev, "ctrl", GPIOD_ASIS);
if (IS_ERR(led->ctrl_gpio)) {
ret = PTR_ERR(led->ctrl_gpio);
dev_err(dev, "cannot get ctrl-gpios %d\n", ret);
return ret;
}
led->aux_gpio = devm_gpiod_get(dev, "aux", GPIOD_ASIS);
if (IS_ERR(led->aux_gpio)) {
ret = PTR_ERR(led->aux_gpio);
dev_err(dev, "cannot get aux-gpios %d\n", ret);
return ret;
}
led->regulator = devm_regulator_get(dev, "vin");
if (IS_ERR(led->regulator))
led->regulator = NULL;
if (led->regulator) {
ret = regulator_enable(led->regulator);
if (ret)
dev_err(dev, "Failed to enable supply: %d\n", ret);
}
child_node = of_get_next_available_child(np, NULL);
if (!child_node) {
dev_err(dev, "No DT child node found for connected LED.\n");
return -EINVAL;
}
led->fled_cdev.led_cdev.name =
of_get_property(child_node, "label", NULL) ? : child_node->name;
ret = of_property_read_u32(child_node, "led-max-microamp",
&cfg->movie_max_microamp);
if (ret) {
dev_err(dev, "failed to parse led-max-microamp\n");
goto err_parse_dt;
}
ret = of_property_read_u32(child_node, "flash-max-microamp",
&cfg->flash_max_microamp);
if (ret) {
dev_err(dev, "failed to parse flash-max-microamp\n");
goto err_parse_dt;
}
ret = of_property_read_u32(child_node, "flash-max-timeout-us",
&cfg->flash_max_timeout);
if (ret) {
dev_err(dev, "failed to parse flash-max-timeout-us\n");
goto err_parse_dt;
}
err_parse_dt:
of_node_put(child_node);
return ret;
}
static const struct led_flash_ops flash_ops = {
.strobe_set = ktd2692_led_flash_strobe_set,
.timeout_set = ktd2692_led_flash_timeout_set,
};
static int ktd2692_probe(struct platform_device *pdev)
{
struct ktd2692_context *led;
struct led_classdev *led_cdev;
struct led_classdev_flash *fled_cdev;
struct ktd2692_led_config_data led_cfg;
int ret;
led = devm_kzalloc(&pdev->dev, sizeof(*led), GFP_KERNEL);
if (!led)
return -ENOMEM;
fled_cdev = &led->fled_cdev;
led_cdev = &fled_cdev->led_cdev;
ret = ktd2692_parse_dt(led, &pdev->dev, &led_cfg);
if (ret)
return ret;
ktd2692_init_flash_timeout(fled_cdev, &led_cfg);
ktd2692_init_movie_current_max(&led_cfg);
fled_cdev->ops = &flash_ops;
led_cdev->max_brightness = led_cfg.max_brightness;
led_cdev->brightness_set_blocking = ktd2692_led_brightness_set;
led_cdev->flags |= LED_CORE_SUSPENDRESUME | LED_DEV_CAP_FLASH;
mutex_init(&led->lock);
platform_set_drvdata(pdev, led);
ret = led_classdev_flash_register(&pdev->dev, fled_cdev);
if (ret) {
dev_err(&pdev->dev, "can't register LED %s\n", led_cdev->name);
mutex_destroy(&led->lock);
return ret;
}
ktd2692_setup(led);
return 0;
}
static int ktd2692_remove(struct platform_device *pdev)
{
struct ktd2692_context *led = platform_get_drvdata(pdev);
int ret;
led_classdev_flash_unregister(&led->fled_cdev);
if (led->regulator) {
ret = regulator_disable(led->regulator);
if (ret)
dev_err(&pdev->dev,
"Failed to disable supply: %d\n", ret);
}
mutex_destroy(&led->lock);
return 0;
}
static const struct of_device_id ktd2692_match[] = {
{ .compatible = "kinetic,ktd2692", },
{ /* sentinel */ },
};
MODULE_DEVICE_TABLE(of, ktd2692_match);
static struct platform_driver ktd2692_driver = {
.driver = {
.name = "ktd2692",
.of_match_table = ktd2692_match,
},
.probe = ktd2692_probe,
.remove = ktd2692_remove,
};
module_platform_driver(ktd2692_driver);
MODULE_AUTHOR("Ingi Kim <ingi2.kim@samsung.com>");
MODULE_DESCRIPTION("Kinetic KTD2692 LED driver");
MODULE_LICENSE("GPL v2");
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