Commit c052bf82 authored by Jonas Meurer's avatar Jonas Meurer Committed by Rafael J. Wysocki
Browse files

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: default avatarJonas Meurer <jonas@freesources.org>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 5c0e9de0

Documentation/ABI/testing/sysfs-power

+13 −0
Original line number Diff line number Diff line
@@ -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.

include/linux/suspend.h

+2 −0
Original line number Diff line number Diff line
@@ -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) {}

kernel/power/Kconfig

+4 −1
Original line number Diff line number Diff line
@@ -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

kernel/power/main.c

+33 −0
Original line number Diff line number Diff line
@@ -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,

kernel/power/suspend.c

+1 −1
Original line number Diff line number Diff line
@@ -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);

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