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

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Message-ID: <CAH2r5msMiG8MjhYuVv8ehqkBLKc1Av3hi+2q6zwrrXdTTa_+YQ@mail.gmail.com>
Date:	Mon, 31 Oct 2011 18:45:48 -0500
From:	Steve French <smfrench@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Tejun Heo <tj@...nel.org>, 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 6:24 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Monday, October 31, 2011, Tejun Heo wrote:
>> Commit 27920651fe "PM / Freezer: Make fake_signal_wake_up() wake
>> TASK_KILLABLE tasks too" made freezer wake up tasks in TASK_KILLABLE
>> sleep too citing non-interruptible but killable sleeps in cifs and
>> nfs.
>>
>> I don't think we can do this.  We should not send spurious unsolicited
>> non-interruptible wakeups.  Most synchornization constructs are built
>> to cope with spurious wakeups and any INTERRUPTIBLE sleep must be able
>> to handle spurious wakeups but that's not true for KILLABLE sleeps -
>> KILLABLE condition cannot be cancelled.
>>
>> 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?
>
> One patch depending on that change has been merged already and I have two
> more in the queue, so I'd like to clarify this ASAP.  Jeff, Steve?
>
>> 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.

-- 
Thanks,

Steve
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