linux-kernel - Re: question on resume()

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Message-Id: <200701301732.56444.rjw@sisk.pl>
Date:	Tue, 30 Jan 2007 17:32:55 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	nigel@...el.suspend2.net
Cc:	Oliver Neukum <oliver@...kum.org>, linux-kernel@...r.kernel.org
Subject: Re: question on resume()

On Tuesday, 30 January 2007 00:10, Rafael J. Wysocki wrote:
> Hi,
> 
> On Monday, 29 January 2007 22:21, Nigel Cunningham wrote:
> > Hi.
> > 
> > On Mon, 2007-01-29 at 22:04 +0100, Oliver Neukum wrote:
> > > Am Montag, 29. Januar 2007 21:14 schrieb Nigel Cunningham:
> > > > Hi.
> > > > 
> > > > On Mon, 2007-01-29 at 12:34 +0100, Oliver Neukum wrote:
> > > > > Am Montag, 29. Januar 2007 12:24 schrieb Nigel Cunningham:
> > > > > > Hi.
> > > > > > 
> > > > > > On Mon, 2007-01-29 at 12:06 +0100, Oliver Neukum wrote:
> > > > > > > Hi,
> > > > > > > 
> > > > > > > may a driver call wake_up() while doing resume() ?
> > > > > > 
> > > > > > I assume you mean waking a userspace process from drivers_resume(). If
> > > > > > so, the answer is no - processes will still be frozen at the point. In
> > > > > > the case of Suspend2, the LRU pages will still not have been read
> > > > > > either, so Suspend2 users would hate you for making hibernation crash
> > > > > > and burn :)
> > > > > 
> > > > > If so, how do I notify tasks presumably about to be thawed that their
> > > > > IO failed?
> > > > 
> > > > Do you mean I/O to disk? If so, it won't fail. All pending I/O gets
> > > > processed like normal either before or after suspending and resuming.
> > > > 
> > > > If you mean something like a packet being transmitted over the network,
> > > > you should be using the normal paths for recording success/failure.
> > > 
> > > I am talking about a character device that puts requests onto a queue.
> > > If the queue is restarted after resumption the normal error path is waking
> > > up the waiting tasks.
> > 
> > Ok. In that case, you'd want to delay trying to wake them until resuming
> > is completed.
> > 
> > Unless there's something I've forgotten, we don't currently have an easy
> > way for you to determine when processes are thawed.
> 
> That's correct.

However, you can always inspect the PF_FROZEN flag of the tasks in question
if that's practicable.

So, while we do not have a mechanism for checking if all tasks have been
thawed, we can do it on a per-task basis quite easily.

Greetings,
Rafael


-- 
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