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

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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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2
include/linux/suspend.h
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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) {}