linux-kernel - Re: [RFC 2/5] fs: freeze on suspend and thaw on resume

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Message-ID: <nycvar.YFH.7.76.1710032203580.17517@jbgna.fhfr.qr>
Date:   Tue, 3 Oct 2017 22:06:14 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
cc:     viro@...iv.linux.org.uk, bart.vanassche@....com,
        ming.lei@...hat.com, tytso@....edu, darrick.wong@...cle.com,
        rjw@...ysocki.net, pavel@....cz, len.brown@...el.com,
        linux-fsdevel@...r.kernel.org, boris.ostrovsky@...cle.com,
        jgross@...e.com, todd.e.brandt@...ux.intel.com, nborisov@...e.com,
        jack@...e.cz, martin.petersen@...cle.com, ONeukum@...e.com,
        oleksandr@...alenko.name, oleg.b.antonyan@...il.com,
        linux-pm@...r.kernel.org, linux-block@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/5] fs: freeze on suspend and thaw on resume

On Tue, 3 Oct 2017, Luis R. Rodriguez wrote:

> This uses the existing filesystem freeze and thaw callbacks to
> freeze each filesystem on suspend/hibernation and thaw upon resume.
> 
> This is needed so that we properly really stop IO in flight without
> races after userspace has been frozen. Without this we rely on
> kthread freezing and its semantics are loose and error prone.
> For instance, even though a kthread may use try_to_freeze() and end
> up being frozen we have no way of being sure that everything that
> has been spawned asynchronously from it (such as timers) have also
> been stopped as well.
> 
> A long term advantage of also adding filesystem freeze / thawing
> supporting durign suspend / hibernation is that long term we may
> be able to eventually drop the kernel's thread freezing completely
> as it was originally added to stop disk IO in flight as we hibernate
> or suspend.
> 
> This also implies that many kthread users exist which have been
> adding freezer semantics onto its kthreads without need. These also
> will need to be reviewed later.
> 
> This is based on prior work originally by Rafael Wysocki and later by
> Jiri Kosina.
> 
> Signed-off-by: Luis R. Rodriguez <mcgrof@...nel.org>

Thanks a lot for picking this up; I never found time to actually finalize 
it.

	Acked-by: Jiri Kosina <jkosina@...e.cz>

for patches 2 and 5 (the fs agnostic code), which were in the core of my 
original work.

-- 
Jiri Kosina
SUSE Labs