Re: [RFC PATCH] freezer: revert 27920651fe "PM / Freezer: Make fake_signal_wake_up() wake TASK_KILLABLE tasks too"

From: Rafael J. Wysocki
Date: Mon Oct 31 2011 - 19:21:43 EST

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@xxxxxxxxxx>
> Cc: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
> Neil, Steve, do the network filesystems need a way to indicate "I can
> either be killed or enter freezer"?
> Thanks.
> kernel/freezer.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> diff --git a/kernel/freezer.c b/kernel/freezer.c
> index 66a594e..7b01de9 100644
> --- a/kernel/freezer.c
> +++ b/kernel/freezer.c
> @@ -67,7 +67,7 @@ static void fake_signal_wake_up(struct task_struct *p)
> unsigned long flags;
> spin_lock_irqsave(&p->sighand->siglock, flags);
> - signal_wake_up(p, 1);
> + signal_wake_up(p, 0);
> spin_unlock_irqrestore(&p->sighand->siglock, flags);
> }

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