[PATCH v3] power: suspend: Move dpm_watchdog to suspend.c and enhance it

From: Joseph Jang
Date: Fri Oct 23 2020 - 02:04:33 EST

Since dpm_watchdog just cover device power management, we proposed to
move it to core power suspend.c to cover not only device power management
hang issues, but also core power management hand issues.

Since dpm_watchdog stands for device pm, we propose to use new name sleep
timer and new timeout handler to cover more sleep hang issues. The new
timeout handler will dump disk sleep task at first round timeout and
trigger kernel panic at second round timeout.
The default timer for each round is defined in
CONFIG_PM_SLEEP_TIMER_TIMEOUT.

Signed-off-by: Joseph Jang <josephjang@xxxxxxxxxx>
---
Changes since v2:
- Add kernel/power/suspend_timer.h in MAINTAINERS
- Share some corner cases that dpm_watchdog cannot cover.
Case#A: dpm_watchdog cannot cover suspend hang in suspend_enter().
File: kernel/power/suspend.c
int suspend_devices_and_enter(suspend_state_t state)
{
... <SNIP>

suspend_test_start();
error = dpm_suspend_start(PMSG_SUSPEND); <== dpm_watchdog will be enabled/disabled in this fucntion ...
if (error) {
pr_err("Some devices failed to suspend, or early wake event detected\n");
goto Recover_platform;
}
suspend_test_finish("suspend devices");
if (suspend_test(TEST_DEVICES))
goto Recover_platform;

do {
error = suspend_enter(state, &wakeup); <== but we encounter hang inside function suspend_enter() ...
} while (!error && !wakeup && platform_suspend_again(state));

Case#B: dpm_watchdog cannot cover resume hang in dpm_resume_early() because it enable/disable in device_resume().
Call trace:
__switch_to+0x174/0x194
__schedule+0xa60/0x1464
__cancel_work_timer+0x120/0x234
chg_pm_resume+0x2c/0xd8
dpm_run_callback+0x27c/0x624
device_resume_early+0x1e4/0x1f8
dpm_resume_early+0x350/0x8f4
suspend_devices_and_enter+0xffc/0x168c
pm_suspend+0xb54/0xdac

File: drivers/base/power/main.c.
static int device_resume(struct device *dev, pm_message_t state, bool async)
if (!dpm_wait_for_superior(dev, async))
goto Complete;

dpm_watchdog_set(&wd, dev);
device_lock(dev);

/*
... <SNIP>

Unlock:
device_unlock(dev);
dpm_watchdog_clear(&wd);

Case#C: dpm_watchdog cannot cover suspend hang in ksys_sync().
Call trace:
__switch_to+0x1b0/0x1cc
__schedule+0xac8/0x1314
io_schedule+0x94/0xc8
wait_on_page_bit+0x1f8/0x3a4
__filemap_fdatawait_range+0x134/0x150
sync_inodes_sb+0x368/0x584
sync_inodes_one_sb+0x18/0x24
iterate_supers+0x12c/0x2b8
ksys_sync+0x48/0x12c
enter_state+0x294/0x7bc
pm_suspend+0x164/0x2a8

- Explain some enhancement by following.
Q1: Why not use the existing one?
struct dpm_watchdog {
struct device *dev;
struct task_struct *tsk;
struct timer_list timer;
};

A1: In kernel/power/suspend.c, we don't have "struct device " because suspend.c is for core PM instead of device PM.
So we propose to use sleep_timer struct.

struct sleep_timer {
struct task_struct *tsk;
struct timer_list timer;
};


Q2: Why not use stack memory for timer struct?
static void dpm_watchdog_set(struct dpm_watchdog *wd, struct device *dev)
{
... <SNIP>
timer_setup_on_stack(timer, dpm_watchdog_handler, 0); <== dpm_watchdog use stack memory for timer struct.
/* use same timeout value for both suspend and resume */
timer->expires = jiffies + HZ * CONFIG_DPM_WATCHDOG_TIMEOUT;
add_timer(timer);
}

A2: dpm_watchdog use stack memory has limitation.
It cannot support starting watchdog at end of function like s2idle_enter().
We cannot use stack memory for this case because the timer struct will be free when go back to caller.

File: kernel/power/suspend.c
static void s2idle_enter(void)
{
trace_suspend_resume(TPS("machine_suspend"), PM_SUSPEND_TO_IDLE, true);

+ stop_sleep_timer(&st);
+
raw_spin_lock_irq(&s2idle_lock);
if (pm_wakeup_pending())
goto out;
... <SNIP>
s2idle_state = S2IDLE_STATE_NONE;
raw_spin_unlock_irq(&s2idle_lock);

+ start_sleep_timer(&st);
+
trace_suspend_resume(TPS("machine_suspend"), PM_SUSPEND_TO_IDLE, false);
}

So we propose to declare a global sleep timer struct in suspend.c like following.

File: kernel/power/suspend.c
static DEFINE_RAW_SPINLOCK(s2idle_lock);

+DECLARE_SLEEP_TIMER(st);
+
/**
* pm_suspend_default_s2idle - Check if suspend-to-idle is the default suspend.

Using global timer has another advantage is we could support double calling add_timer()
because add_timer() can easily to delete pending timer and add new timer by using the
same timer struct.

Q3: Why do you need to change the timeout handler?
A3: dpm_watchdog_handler() need device struct to get device information, but suspend.c doesn't have it.
In most of cases, we could know which device driver hang by tracing the suspend thread call stack logs
without device struct information for debugging. So we propose to remove device struct and related
information like "dev_driver_string(wd->dev)" and "dev_name(wd->dev)" from timeout handler.

static void dpm_watchdog_handler(struct timer_list *t)
{
struct dpm_watchdog *wd = from_timer(wd, t, timer);

dev_emerg(wd->dev, "**** DPM device timeout ****\n");
show_stack(wd->tsk, NULL, KERN_EMERG);
panic("%s %s: unrecoverable failure\n",
dev_driver_string(wd->dev), dev_name(wd->dev)); <== we don't need it.
}

We propose to dump all disk sleep tasks call stack log twice to double confirm suspend thread hang at
the same function and make sure other sleep tasks were stuck at the same function for a long time.
We also try to resume console if the console is suspended.
At the end of watchdog timeout handler, we propose to trigger kernel panic to prevent system hang like
dpm_watchdog.


static void sleep_timeout_handler(struct timer_list *t)
{
struct sleep_timer *st = from_timer(st, t, timer);
static int timeout_count;

pr_info("Sleep timeout (timer is %d seconds)\n",
(CONFIG_PM_SLEEP_TIMER_TIMEOUT));
show_stack(st->tsk, NULL, KERN_EMERG);
show_state_filter(TASK_UNINTERRUPTIBLE);

if (timeout_count < 1) {
timeout_count++;
start_sleep_timer(st);
return;
}

if (console_is_suspended())
resume_console();

panic("Sleep timeout and panic\n");
}

Changes since v1:
- Add commit message to explain why move dpm_watchdog to kernel/power/suspend.c.
- Remove dpm_watchdog related functions in drivers/base/power/main.c.
- Move suspend_timer.h from include/linux/ to kernel/power/.
---
MAINTAINERS | 2 +
drivers/base/power/main.c | 69 ---------------------------
include/linux/console.h | 1 +
kernel/power/Kconfig | 27 ++++++-----
kernel/power/suspend.c | 19 ++++++++
kernel/power/suspend_timer.h | 90 ++++++++++++++++++++++++++++++++++++
kernel/printk/printk.c | 5 ++
7 files changed, 130 insertions(+), 83 deletions(-)
create mode 100644 kernel/power/suspend_timer.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 867157311dc8..370e7c68f0c3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7787,6 +7787,7 @@ F: drivers/base/power/
F: include/linux/freezer.h
F: include/linux/pm.h
F: include/linux/suspend.h
+F: kernel/power/suspend_timer.h
F: kernel/power/

HID CORE LAYER
@@ -16629,6 +16630,7 @@ F: drivers/base/power/
F: include/linux/freezer.h
F: include/linux/pm.h
F: include/linux/suspend.h
+F: kernel/power/suspend_timer.h
F: kernel/power/

SVGA HANDLING
diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index 205a06752ca9..b08f91e31a70 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -496,69 +496,6 @@ static int dpm_run_callback(pm_callback_t cb, struct device *dev,
return error;
}

-#ifdef CONFIG_DPM_WATCHDOG
-struct dpm_watchdog {
- struct device *dev;
- struct task_struct *tsk;
- struct timer_list timer;
-};
-
-#define DECLARE_DPM_WATCHDOG_ON_STACK(wd) \
- struct dpm_watchdog wd
-
-/**
- * dpm_watchdog_handler - Driver suspend / resume watchdog handler.
- * @t: The timer that PM watchdog depends on.
- *
- * Called when a driver has timed out suspending or resuming.
- * There's not much we can do here to recover so panic() to
- * capture a crash-dump in pstore.
- */
-static void dpm_watchdog_handler(struct timer_list *t)
-{
- struct dpm_watchdog *wd = from_timer(wd, t, timer);
-
- dev_emerg(wd->dev, "**** DPM device timeout ****\n");
- show_stack(wd->tsk, NULL, KERN_EMERG);
- panic("%s %s: unrecoverable failure\n",
- dev_driver_string(wd->dev), dev_name(wd->dev));
-}
-
-/**
- * dpm_watchdog_set - Enable pm watchdog for given device.
- * @wd: Watchdog. Must be allocated on the stack.
- * @dev: Device to handle.
- */
-static void dpm_watchdog_set(struct dpm_watchdog *wd, struct device *dev)
-{
- struct timer_list *timer = &wd->timer;
-
- wd->dev = dev;
- wd->tsk = current;
-
- timer_setup_on_stack(timer, dpm_watchdog_handler, 0);
- /* use same timeout value for both suspend and resume */
- timer->expires = jiffies + HZ * CONFIG_DPM_WATCHDOG_TIMEOUT;
- add_timer(timer);
-}
-
-/**
- * dpm_watchdog_clear - Disable suspend/resume watchdog.
- * @wd: Watchdog to disable.
- */
-static void dpm_watchdog_clear(struct dpm_watchdog *wd)
-{
- struct timer_list *timer = &wd->timer;
-
- del_timer_sync(timer);
- destroy_timer_on_stack(timer);
-}
-#else
-#define DECLARE_DPM_WATCHDOG_ON_STACK(wd)
-#define dpm_watchdog_set(x, y)
-#define dpm_watchdog_clear(x)
-#endif
-
/*------------------------- Resume routines -------------------------*/

/**
@@ -899,7 +836,6 @@ static int device_resume(struct device *dev, pm_message_t state, bool async)
pm_callback_t callback = NULL;
const char *info = NULL;
int error = 0;
- DECLARE_DPM_WATCHDOG_ON_STACK(wd);

TRACE_DEVICE(dev);
TRACE_RESUME(0);
@@ -916,7 +852,6 @@ static int device_resume(struct device *dev, pm_message_t state, bool async)
if (!dpm_wait_for_superior(dev, async))
goto Complete;

- dpm_watchdog_set(&wd, dev);
device_lock(dev);

/*
@@ -969,7 +904,6 @@ static int device_resume(struct device *dev, pm_message_t state, bool async)

Unlock:
device_unlock(dev);
- dpm_watchdog_clear(&wd);

Complete:
complete_all(&dev->power.completion);
@@ -1593,7 +1527,6 @@ static int __device_suspend(struct device *dev, pm_message_t state, bool async)
pm_callback_t callback = NULL;
const char *info = NULL;
int error = 0;
- DECLARE_DPM_WATCHDOG_ON_STACK(wd);

TRACE_DEVICE(dev);
TRACE_SUSPEND(0);
@@ -1647,7 +1580,6 @@ static int __device_suspend(struct device *dev, pm_message_t state, bool async)
dev->power.may_skip_resume = true;
dev->power.must_resume = false;

- dpm_watchdog_set(&wd, dev);
device_lock(dev);

if (dev->pm_domain) {
@@ -1699,7 +1631,6 @@ static int __device_suspend(struct device *dev, pm_message_t state, bool async)
}

device_unlock(dev);
- dpm_watchdog_clear(&wd);

Complete:
if (error)
diff --git a/include/linux/console.h b/include/linux/console.h
index 0670d3491e0e..5436d8dc600f 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -192,6 +192,7 @@ static inline void console_sysfs_notify(void)
{ }
#endif
extern bool console_suspend_enabled;
+extern int console_is_suspended(void);

/* Suspend and resume console messages over PM events */
extern void suspend_console(void);
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index a7320f07689d..fa021837473b 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -207,21 +207,20 @@ config PM_SLEEP_DEBUG
def_bool y
depends on PM_DEBUG && PM_SLEEP

-config DPM_WATCHDOG
- bool "Device suspend/resume watchdog"
- depends on PM_DEBUG && PSTORE && EXPERT
+config PM_SLEEP_MONITOR
+ bool "Linux kernel suspend/resume process monitor"
+ depends on PM_SLEEP
help
- Sets up a watchdog timer to capture drivers that are
- locked up attempting to suspend/resume a device.
- A detected lockup causes system panic with message
- captured in pstore device for inspection in subsequent
- boot session.
-
-config DPM_WATCHDOG_TIMEOUT
- int "Watchdog timeout in seconds"
- range 1 120
- default 120
- depends on DPM_WATCHDOG
+ This option will enable sleep timer to prevent device stuck
+ during suspend/resume process. Sleep timeout handler will dump
+ disk sleep task at first round timeout and trigger kernel panic
+ at second round timeout. The timer for each round is defined in
+ CONFIG_PM_SLEEP_TIMER_TIMEOUT.
+
+config PM_SLEEP_TIMER_TIMEOUT
+ int "Sleep timer timeout in seconds"
+ range 30 120
+ depends on PM_SLEEP_MONITOR

config PM_TRACE
bool
diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index 8b1bb5ee7e5d..0272494e0d0e 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -32,6 +32,7 @@
#include <linux/moduleparam.h>

#include "power.h"
+#include "suspend_timer.h"

const char * const pm_labels[] = {
[PM_SUSPEND_TO_IDLE] = "freeze",
@@ -61,6 +62,8 @@ static DECLARE_SWAIT_QUEUE_HEAD(s2idle_wait_head);
enum s2idle_states __read_mostly s2idle_state;
static DEFINE_RAW_SPINLOCK(s2idle_lock);

+DECLARE_SLEEP_TIMER(st);
+
/**
* pm_suspend_default_s2idle - Check if suspend-to-idle is the default suspend.
*
@@ -89,6 +92,8 @@ static void s2idle_enter(void)
{
trace_suspend_resume(TPS("machine_suspend"), PM_SUSPEND_TO_IDLE, true);

+ stop_sleep_timer(&st);
+
raw_spin_lock_irq(&s2idle_lock);
if (pm_wakeup_pending())
goto out;
@@ -114,6 +119,8 @@ static void s2idle_enter(void)
s2idle_state = S2IDLE_STATE_NONE;
raw_spin_unlock_irq(&s2idle_lock);

+ start_sleep_timer(&st);
+
trace_suspend_resume(TPS("machine_suspend"), PM_SUSPEND_TO_IDLE, false);
}

@@ -179,6 +186,8 @@ void __init pm_states_init(void)
* initialize mem_sleep_states[] accordingly here.
*/
mem_sleep_states[PM_SUSPEND_TO_IDLE] = mem_sleep_labels[PM_SUSPEND_TO_IDLE];
+
+ init_sleep_timer(&st, sleep_timeout_handler);
}

static int __init mem_sleep_default_setup(char *str)
@@ -426,6 +435,8 @@ static int suspend_enter(suspend_state_t state, bool *wakeup)
if (error || suspend_test(TEST_CPUS))
goto Enable_cpus;

+ stop_sleep_timer(&st);
+
arch_suspend_disable_irqs();
BUG_ON(!irqs_disabled());

@@ -451,6 +462,8 @@ static int suspend_enter(suspend_state_t state, bool *wakeup)
arch_suspend_enable_irqs();
BUG_ON(irqs_disabled());

+ start_sleep_timer(&st);
+
Enable_cpus:
suspend_enable_secondary_cpus();

@@ -610,6 +623,9 @@ int pm_suspend(suspend_state_t state)
return -EINVAL;

pr_info("suspend entry (%s)\n", mem_sleep_labels[state]);
+
+ start_sleep_timer(&st);
+
error = enter_state(state);
if (error) {
suspend_stats.fail++;
@@ -617,6 +633,9 @@ int pm_suspend(suspend_state_t state)
} else {
suspend_stats.success++;
}
+
+ stop_sleep_timer(&st);
+
pr_info("suspend exit\n");
return error;
}
diff --git a/kernel/power/suspend_timer.h b/kernel/power/suspend_timer.h
new file mode 100644
index 000000000000..7e4c9e31bf09
--- /dev/null
+++ b/kernel/power/suspend_timer.h
@@ -0,0 +1,90 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_SLEEP_TIMER_H
+#define _LINUX_SLEEP_TIMER_H
+
+#include <linux/sched/debug.h>
+
+#ifdef CONFIG_PM_SLEEP_MONITOR
+struct sleep_timer {
+ struct task_struct *tsk;
+ struct timer_list timer;
+};
+
+#define DECLARE_SLEEP_TIMER(st) \
+ struct sleep_timer st
+
+/**
+ * init_sleep_timer - Initialize sleep timer.
+ * @st: Sleep timer to initialize.
+ * @func: Sleep timer timeout handler.
+ */
+static void init_sleep_timer(struct sleep_timer *st, void (*func))
+{
+ struct timer_list *timer = &st->timer;
+
+ timer_setup(timer, func, 0);
+}
+
+/**
+ * start_sleep_timer - Enable sleep timer to monitor suspend thread.
+ * @st: Sleep timer to enable.
+ */
+static void start_sleep_timer(struct sleep_timer *st)
+{
+ struct timer_list *timer = &st->timer;
+
+ st->tsk = current;
+
+ /* use same timeout value for both suspend and resume */
+ timer->expires = jiffies + HZ * CONFIG_PM_SLEEP_TIMER_TIMEOUT;
+ add_timer(timer);
+}
+
+/**
+ * stop_sleep_timer - Disable sleep timer.
+ * @st: sleep timer to disable.
+ */
+static void stop_sleep_timer(struct sleep_timer *st)
+{
+ struct timer_list *timer = &st->timer;
+
+ del_timer_sync(timer);
+}
+
+/**
+ * sleep_timeout_handler - sleep timer timeout handler.
+ * @t: The timer list that sleep timer depends on.
+ *
+ * Called when suspend thread has timeout suspending or resuming.
+ * Dump all uninterruptible tasks' call stack and call panic() to
+ * reboot system in second round timeout.
+ */
+static void sleep_timeout_handler(struct timer_list *t)
+{
+ struct sleep_timer *st = from_timer(st, t, timer);
+ static int timeout_count;
+
+ pr_info("Sleep timeout (timer is %d seconds)\n",
+ (CONFIG_PM_SLEEP_TIMER_TIMEOUT));
+ show_stack(st->tsk, NULL, KERN_EMERG);
+ show_state_filter(TASK_UNINTERRUPTIBLE);
+
+ if (timeout_count < 1) {
+ timeout_count++;
+ start_sleep_timer(st);
+ return;
+ }
+
+ if (console_is_suspended())
+ resume_console();
+
+ panic("Sleep timeout and panic\n");
+}
+#else
+#define DECLARE_SLEEP_TIMER(st)
+#define init_sleep_timer(x, y)
+#define start_sleep_timer(x)
+#define stop_sleep_timer(x)
+#endif
+
+#endif /* _LINUX_SLEEP_TIMER_H */
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 9b75f6bfc333..488cbc9abaaf 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2259,6 +2259,11 @@ module_param_named(console_suspend, console_suspend_enabled,
MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
" and hibernate operations");

+int console_is_suspended(void)
+{
+ return console_suspended;
+}
+
/**
* suspend_console - suspend the console subsystem
*
--
2.29.0.rc2.309.g374f81d7ae-goog