linux-kernel - Re: [RFC 5/5] pm: remove kernel thread freezing

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Date:   Wed, 4 Oct 2017 18:18:03 +1100
From:   Dave Chinner <david@...morbit.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>, viro@...iv.linux.org.uk,
        bart.vanassche@....com, ming.lei@...hat.com, tytso@....edu,
        darrick.wong@...cle.com, jikos@...nel.org, 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 5/5] pm: remove kernel thread freezing

On Wed, Oct 04, 2017 at 02:47:56AM +0200, Luis R. Rodriguez wrote:
> On Tue, Oct 03, 2017 at 11:15:07PM +0200, Rafael J. Wysocki wrote:
> > On Tuesday, October 3, 2017 8:59:00 PM CEST Rafael J. Wysocki wrote:
> > > On Tuesday, October 3, 2017 8:53:13 PM CEST Luis R. Rodriguez wrote:
> > > > Now that all filesystems which used to rely on kthread
> > > > freezing have been converted to filesystem freeze/thawing
> > > > we can remove the kernel kthread freezer.
> > > > 
> > > > Signed-off-by: Luis R. Rodriguez <mcgrof@...nel.org>
> > > 
> > > I like this one. :-)
> > 
> > However, suspend_freeze/thaw_processes() require some more work.
> > 
> > In particular, the freezing of workqueues is being removed here
> > without a replacement.
> 
> Hrm, where do you see that? freeze_workqueues_busy() is still called on
> try_to_freeze_tasks(). Likewise thaw_processes() also calls thaw_workqueues().
> I did forget to nuke pm_nosig_freezing though.

static int try_to_freeze_tasks(bool user_only)
{
.....
        if (!user_only)
		freeze_workqueues_begin();
.....
                if (!user_only) {
			wq_busy = freeze_workqueues_busy();
.....
}

i.e. only try_to_freeze_tasks(false) will freeze workqueues, and the
only function that calls that - freeze_kernel_threads() - is removed
by this patch.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com