PERFORCE change 103633 for review
Divacky Roman
xdivac02 at stud.fit.vutbr.cz
Fri Aug 11 12:13:23 UTC 2006
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 at 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.
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