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 19:02:11 -0500
From:	Steve French <smfrench@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	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"

On Mon, Oct 31, 2011 at 6:53 PM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Mon, Oct 31, 2011 at 06:45:48PM -0500, Steve French wrote:
>> >> Signed-off-by: Tejun Heo <tj@...nel.org>
>> >> Cc: Jeff Layton <jlayton@...hat.com>
>> >> ---
>> >> Neil, Steve, do the network filesystems need a way to indicate "I can
>> >> either be killed or enter freezer"?
>>
>> Probably, yes, but I will defer to Jeff as he has looked
>> more recently at these issues.
>>
>> I can explain cifs state, and disconnect/reconnection of sessions
>> (and smb2 is a little more feature rich in this regard), but will
>> let Jeff explain the more subtle points you are getting at.
>
> Hmmm... I'm getting confused.
>
> For nfs, this really is a non-issue.  Either the user wants nointr or
> intr behavior.  NFS nointr is rather crazy - it's basically "nothing
> can do anything to tasks which is doing NFS IO until it's complete"
> and really meant to be used for servers sharing filesystems for /usr,
> /home and stuff.  It doesn't make whole lot of sense on systems which
> may go suspend and that's why there's intr option.
>
> I suppose the problem is that cifs doesn't know how to do 'intr' yet,
> right?  If that really is the problem, the correct long term solution
> would be implementing proper intr behavior and it doesn't make any
> sense to push this type of change to PM core to for short term
> workaround.  Just use prepare_to_wait() / schedule() / finish_wait()
> directly w/ INTERRUPTIBLE sleep and don't break out of wait loop on
> signal_pending().  If this should be used in multiple places, write up
> a wait_event_XXX() wrapper.  There is absolutely no reason to change
> wakeup condition.

It isn't that simple (among other reasons due to much time waiting
in the socket interface), but since this directly addresses problems
Jeff has spent much time debugging, I would like him to chime in.


-- 
Thanks,

Steve
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