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

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Date:   Tue, 3 Oct 2017 23:18:46 +0200
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Shuah Khan <shuahkhan@...il.com>
Cc:     Jiri Kosina <jikos@...nel.org>, mchehab@...pensource.com,
        Pavel Machek <pavel@....cz>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>, viro@...iv.linux.org.uk,
        bart.vanassche@....com, ming.lei@...hat.com, tytso@....edu,
        darrick.wong@...cle.com, rjw@...ysocki.net, 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 list <linux-pm@...r.kernel.org>,
        linux-block@...r.kernel.org, linux-xfs@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, linux-media@...r.kernel.org,
        shuahkh@....samsung.com
Subject: Re: [RFC 5/5] pm: remove kernel thread freezing

On Tue, Oct 03, 2017 at 03:09:53PM -0600, Shuah Khan wrote:
> On Tue, Oct 3, 2017 at 3:00 PM, Jiri Kosina <jikos@...nel.org> wrote:
> > On Tue, 3 Oct 2017, Pavel Machek wrote:
> >
> >> > Again, I agree that the (rare) kthreads that are actually "creating" new
> >> > I/O have to be somehow frozen and require special care.
> >>
> >> Agreed. Was any effort made to identify those special kernel threads?
> >
> > I don't think there is any other way than just inspecting all the
> > try_to_freeze() instances in the kernel, and understanding what that
> > particular kthread is doing.
> >
> > I've cleaned up most of the low-hanging fruit already, where the
> > try_to_freeze() was obviously completely pointless, but a lot more time
> > needs to be invested into this.
> >
> 
> There are about 36 drivers that call try_to_freeze() and half (18 ) of
> those are media drivers. Maybe it is easier handle sub-system by
> sub-system basis for a review of which one of these usages could be
> removed. cc'ing Mauro and linux-media

Yes :)

I guess no one reads cover letters, but indeed. To be clear, this last
patch should only go in after a few kernels from now all kthreads
are vetted for piece-meal wise.

This patch would be the nail on the kthread freezer coffin. It should
go in last, who knows how many years from now, and if ever.

  Luis