linux-kernel - Re: [RFC 4/5] ext4: add fs freezing support on suspend/hibernation

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Date:   Wed, 4 Oct 2017 12:48:39 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Dave Chinner <david@...morbit.com>
Cc:     "Luis R. Rodriguez" <mcgrof@...nel.org>, viro@...iv.linux.org.uk,
        bart.vanassche@....com, ming.lei@...hat.com,
        darrick.wong@...cle.com, jikos@...nel.org, 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 4/5] ext4: add fs freezing support on suspend/hibernation

On Wed, Oct 04, 2017 at 06:05:23PM +1100, Dave Chinner wrote:
> Basically, before thawing filesystems the rest of the kernel
> infrastructure needs to have been restarted. i.e. the order
> needs to be:
> 
> freeze userspace
> freeze filesystems
> freeze kernel threads
> freeze workqueues
> 
> thaw workqueues
> thaw kernel threads
> thaw filesystems
> thaw userspace
> 
> and it should end up that way.
> 
> > Or if we have a network block device, or
> > something else in the storage stack that needs to run a kernel thread
> > context (or a workqueue, etc.) --- is the fact that userspace is
> > frozen mean the scheduler is going to refuse to schedule()?
> 
> No.

Well, that's what the answer *should* be.  I was asking what this
patch series does, and given that Luis reported that with this patch
series ext4_commit_super(sb, 1) is hanging, I have my suspicions about
what the answer might be with this patch set.  (Especially since the
claimed goal of the patch set is, "kthread freezing with filesystem
freeze/thaw".

Cheers,

						- Ted