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

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Date:	Mon, 31 Oct 2011 17:55:05 -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"

Hey, again.

On Mon, Oct 31, 2011 at 04:30:59PM -0700, Tejun Heo wrote:
> 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.

Hmm... I couldn't find KILLABLE used like that but here are two
UNINTERRUPTIBLE sleep examples.

* kthread_start() depends on the fact that a kthread won't be woken up
  from UNINTERRUPTIBLE sleep spuriously.

* jfs_flush_journal() doesn't check whether the wakeup was spurious
  after waiting if !tblkGC_COMMITTED.

Maybe we can re-define KILLABLE as killable && freezable but IMHO that
requires pretty strong rationales.  If at all possible, let's not
diddle with that if it can be worked around some other way.

Thank you.

-- 
tejun
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