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Date: Fri, 11 Aug 2006 14:13:14 +0200
From: Divacky Roman <xdivac02@stud.fit.vutbr.cz>
To: Robert Watson <rwatson@freebsd.org>
Message-ID: <20060811121314.GA85207@stud.fit.vutbr.cz>
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	<20060811124027.K45647@fledge.watson.org>
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Cc: Roman Divacky <rdivacky@freebsd.org>,
	Perforce Change Reviews <perforce@freebsd.org>
Subject: Re: PERFORCE change 103633 for review
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On Fri, Aug 11, 2006 at 12:42:50PM +0100, Robert Watson wrote:
> On Fri, 11 Aug 2006, Roman Divacky wrote:
> 
> >http://perforce.freebsd.org/chv.cgi?CH=103633
> >
> >Change 103633 by rdivacky@rdivacky_witten on 2006/08/11 11:10:09
> >
> >	Giantify futex code - this is necessary because the futex code is 
> >	expected to be atomic.
> >	I need to assure the atomicity. I am using Giant because its 
> >	sleepable mutex. I hope
> >	someone will point me to some other better solution.
> 
> Giant is not "sleepable" in the same sense that sx locks, lockmgr locks, 
> etc, are.  Normally "sleepable" means that the lock can be held across a 
> sleep of potentially unbounded length, such as msleep(), tsleep(), 
> cv_wait(), etc. Giant is automatically dropped by the kernel on sleep, and 
> re-acquired one wakeup.  This means that Giant does not provide mutual 
> exclusion across a sleep -- if this is a property you are relying on, then 
> Giant is not what you want.  If you most sleep while holding a lock, I 
> would recommend an sx lock. However, a preferred solution is not to sleep 
> holding a lock.

yes... sleepable as in "can be held while sleeping no matter how this is acomplished"

I think the main problem (which is now fixed) was with this:

	copyin(addr, val1);
	if (val1 == val2)
	   	....

being non-atomic. On the other hand I tried to use other locks other then Giant and it
didnt work. I hope to investigate that later. Now I have this working and my focus is elsewhere.