PM: suspend: Add sysfs attribute to control the "sync on suspend" behavior

The sysfs attribute `/sys/power/sync_on_suspend` controls, whether or not
filesystems are synced by the kernel before system suspend.

Congruously, the behaviour of build-time switch CONFIG_SUSPEND_SKIP_SYNC
is slightly changed: It now defines the run-tim default for the new sysfs
attribute `/sys/power/sync_on_suspend`.

The run-time attribute is added because the existing corresponding
build-time Kconfig flag for (`CONFIG_SUSPEND_SKIP_SYNC`) is not flexible
enough. E.g. Linux distributions that provide pre-compiled kernels
usually want to stick with the default (sync filesystems before suspend)
but under special conditions this needs to be changed.

One example for such a special condition is user-space handling of
suspending block devices (e.g. using `cryptsetup luksSuspend` or `dmsetup
suspend`) before system suspend. The Kernel trying to sync filesystems
after the underlying block device already got suspended obviously leads
to dead-locks. Be aware that you have to take care of the filesystem sync
yourself before suspending the system in those scenarios.

Signed-off-by: Jonas Meurer <jonas@freesources.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Jonas Meurer 2020-01-16 12:53:54 +01:00 committed by Rafael J. Wysocki
parent 5c0e9de065
commit c052bf82c6
5 changed files with 53 additions and 2 deletions

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@ -407,3 +407,16 @@ Contact: Kalesh Singh <kaleshsingh96@gmail.com>
Description:
The /sys/power/suspend_stats/last_failed_step file contains
the last failed step in the suspend/resume path.
What: /sys/power/sync_on_suspend
Date: October 2019
Contact: Jonas Meurer <jonas@freesources.org>
Description:
This file controls whether or not the kernel will sync()
filesystems during system suspend (after freezing user space
and before suspending devices).
Writing a "1" to this file enables the sync() and writing a "0"
disables it. Reads from the file return the current value.
The default is "1" if the build-time "SUSPEND_SKIP_SYNC" config
flag is unset, or "0" otherwise.

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@ -329,6 +329,7 @@ extern void arch_suspend_disable_irqs(void);
extern void arch_suspend_enable_irqs(void);
extern int pm_suspend(suspend_state_t state);
extern bool sync_on_suspend_enabled;
#else /* !CONFIG_SUSPEND */
#define suspend_valid_only_mem NULL
@ -342,6 +343,7 @@ static inline bool pm_suspend_default_s2idle(void) { return false; }
static inline void suspend_set_ops(const struct platform_suspend_ops *ops) {}
static inline int pm_suspend(suspend_state_t state) { return -ENOSYS; }
static inline bool sync_on_suspend_enabled(void) { return true; }
static inline bool idle_should_enter_s2idle(void) { return false; }
static inline void __init pm_states_init(void) {}
static inline void s2idle_set_ops(const struct platform_s2idle_ops *ops) {}

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@ -27,7 +27,10 @@ config SUSPEND_SKIP_SYNC
Skip the kernel sys_sync() before freezing user processes.
Some systems prefer not to pay this cost on every invocation
of suspend, or they are content with invoking sync() from
user-space before invoking suspend. Say Y if that's your case.
user-space before invoking suspend. There's a run-time switch
at '/sys/power/sync_on_suspend' to configure this behaviour.
This setting changes the default for the run-tim switch. Say Y
to change the default to disable the kernel sys_sync().
config HIBERNATE_CALLBACKS
bool

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@ -190,6 +190,38 @@ static ssize_t mem_sleep_store(struct kobject *kobj, struct kobj_attribute *attr
}
power_attr(mem_sleep);
/*
* sync_on_suspend: invoke ksys_sync_helper() before suspend.
*
* show() returns whether ksys_sync_helper() is invoked before suspend.
* store() accepts 0 or 1. 0 disables ksys_sync_helper() and 1 enables it.
*/
bool sync_on_suspend_enabled = !IS_ENABLED(CONFIG_SUSPEND_SKIP_SYNC);
static ssize_t sync_on_suspend_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sprintf(buf, "%d\n", sync_on_suspend_enabled);
}
static ssize_t sync_on_suspend_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t n)
{
unsigned long val;
if (kstrtoul(buf, 10, &val))
return -EINVAL;
if (val > 1)
return -EINVAL;
sync_on_suspend_enabled = !!val;
return n;
}
power_attr(sync_on_suspend);
#endif /* CONFIG_SUSPEND */
#ifdef CONFIG_PM_SLEEP_DEBUG
@ -855,6 +887,7 @@ static struct attribute * g[] = {
&wakeup_count_attr.attr,
#ifdef CONFIG_SUSPEND
&mem_sleep_attr.attr,
&sync_on_suspend_attr.attr,
#endif
#ifdef CONFIG_PM_AUTOSLEEP
&autosleep_attr.attr,

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@ -564,7 +564,7 @@ static int enter_state(suspend_state_t state)
if (state == PM_SUSPEND_TO_IDLE)
s2idle_begin();
if (!IS_ENABLED(CONFIG_SUSPEND_SKIP_SYNC)) {
if (sync_on_suspend_enabled) {
trace_suspend_resume(TPS("sync_filesystems"), 0, true);
ksys_sync_helper();
trace_suspend_resume(TPS("sync_filesystems"), 0, false);