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Date: Wed, 4 Oct 2017 12:48:39 -0400
From: Theodore Ts'o <tytso@mit.edu>
To: Dave Chinner <david@fromorbit.com>
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>, viro@zeniv.linux.org.uk,
        bart.vanassche@wdc.com, ming.lei@redhat.com,
        darrick.wong@oracle.com, jikos@kernel.org, rjw@rjwysocki.net,
        pavel@ucw.cz, len.brown@intel.com, linux-fsdevel@vger.kernel.org,
        boris.ostrovsky@oracle.com, jgross@suse.com,
        todd.e.brandt@linux.intel.com, nborisov@suse.com, jack@suse.cz,
        martin.petersen@oracle.com, ONeukum@suse.com,
        oleksandr@natalenko.name, oleg.b.antonyan@gmail.com,
        linux-pm@vger.kernel.org, linux-block@vger.kernel.org,
        linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC 4/5] ext4: add fs freezing support on suspend/hibernation
Message-ID: <20171004164839.zyfpx64qmmfv2jtx@thunk.org>
References: <20171003185313.1017-1-mcgrof@kernel.org>
 <20171003185313.1017-5-mcgrof@kernel.org>
 <20171003195930.ivgaccdabxczar62@thunk.org>
 <20171003201321.GE2294@wotan.suse.de>
 <20171004014204.mztkdnm7wb7r6sl2@thunk.org>
 <20171004070523.GE3666@dastard>
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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