linux-kernel - Re: [PATCH v3] PM: suspend: Add sysfs attribute to control the "sync on suspend" behavior

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Date:   Sun, 19 Jan 2020 13:55:58 +0100
From:   Jonas Meurer <jonas@...esources.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Tim Dittler <tim.dittler@...temli.org>,
        Yannik Sembritzki <yannik@...britzki.me>
Subject: Re: [PATCH v3] PM: suspend: Add sysfs attribute to control the "sync
 on suspend" behavior

Hey Rafael,

Rafael J. Wysocki:
> On Thu, Jan 16, 2020 at 12:53 PM Jonas Meurer <jonas@...esources.org> wrote:
>>
>> 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@...esources.org>
> 
> Applied as 5.6 material with minor changes in the ABI document, thanks!

Wow, that's great news. I'm excited to read that the patch finally will
enter the Linux kernel \o/

Thanks a lot for guiding me through my first Linux kernel patch
contribution.

Cheers
 jonas