linux-kernel - Re: [RFC PATCH] freezer: revert 27920651fe "PM / Freezer: Make fake_signal_wake_up() wake TASK

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Message-ID: <20111031233059.GI18855@google.com>
Date:	Mon, 31 Oct 2011 16:30:59 -0700
From:	Tejun Heo <tj@...nel.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Jeff Layton <jlayton@...hat.com>, Steve French <sfrench@...ba.org>,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	linux-pm@...r.kernel.org, linux-cifs@...r.kernel.org,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Neil Brown <neilb@...e.de>
Subject: Re: [RFC PATCH] freezer: revert 27920651fe "PM / Freezer: Make
 fake_signal_wake_up() wake TASK_KILLABLE tasks too"

Hello,

On Tue, Nov 01, 2011 at 12:24:16AM +0100, Rafael J. Wysocki wrote:
> > This is probably okay for most cases but circumventing fundamental
> > wakeup condition like this is asking for trouble.  Furthermore, I'm
> > not sure the behavior change brought on by this change - breaking
> > nfs/cifs uninterruptible operation guarantee - is correct.  If such
> > behavior is desirable, the right thing to do is using intr mount
> > option, not circumventing it from PM layer.
> 
> Do you have any specific examples of breakage, or is it just that you _think_
> it's not quite right?

I can't remember one off the top of my head but I'm pretty sure there
at least are few which expect tight inter-locking between sleeps and
wakeups.  I'll look for examples and post reply.  ISTR them being
kernel threads so this might not apply directly but it's still a
dangerous game to play.

Bugs caused by behaviors like this will be very difficult to reproduce
and diagnose.  There is no reason to play a gamble like this.  If
somebody *really* wants non-interruptible killable & freezable sleep,
we really should be adding TASK_WAKE_FREEZER or something instead of
modifying the behavior of TASK_KILLABLE.

Thanks.

-- 
tejun
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