linux-kernel - Re: apm emulation driver broken ?

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Date:	Sat, 17 Nov 2007 13:46:51 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Franck Bui-Huu <vagabon.xyz@...il.com>
Cc:	linux-pm@...ts.linux-foundation.org,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: apm emulation driver broken ?

On Saturday, 17 of November 2007, Franck Bui-Huu wrote:
> Rafael J. Wysocki wrote:
> > On Saturday, 17 of November 2007, Franck Bui-Huu wrote:
> >> Rafael J. Wysocki wrote:
> >>> However, using PF_NOFREEZE to prevent this from happening doesn't seem to be
> >>> a good idea.
> >>>
> >> Indeed but...
> >>
> >>> I'd probably use wait_event_freezable() (defined in
> >>> include/linux/freezer.h) for that.
> >> ...I would just revert this bits from now to make sure this driver
> >> work again for v2.6.24.
> > 
> > I'd prefer not to.
> > 
> > The PF_NOFREEZE was not present in 2.6.23 already and I wouldn't like to
> > reintroduce it now.
> > 
> > Why do you think that using wait_event_freezable() would not work, BTW?
> > 
> 
> I've never claimed this. I just said it may be safer to revert the
> changes for v2.6.24 and improve the current code for next releases.
> 
> >>> It tries to send them fake signals and waits for them to freeze.  If
> >>> they don't freeze within the timeout, it fails and clears their
> >>> TIF_FREEZE bits.
> >> But send_fake_signal() seems to wake up task in INTERRUPTIBLE state
> >> only. Looking at signal_wake_up(), it basically do:
> >>
> >> 	wake_up_state(t, TASK_INTERRUPTIBLE);
> >>
> >> What am I missing ?
> > 
> > Nothing. :-)
> > 
> > I didn't remember the change that made the freezer use TASK_INTERRUPTIBLE
> > explicitly in there (should have looked at the current code before replying).
> > 
> 
> ok so now we agreed on this point, can we assert that a user
> land thread waiting for an event in an UNINTERRUPTIBLE state
> will prevent a suspend to happen ?

Yes.

Rafael
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