Re: splinter work on generic fs notification framework
On Wed, 2005-07-13 at 09:40 +0100, David Woodhouse wrote:
And _especially_ don't use it for places where the refcount had
other
locking and didn't even need to be atomic.
Actually, Tim, I'll revise that.
The kref stuff seems to be an attempt to provide 'refcounting for
dummies'. However, rather than abstracting the refcounting and making it
safe and easy, it merely hides the potential problems. If you call
kref_put() and kref_get() simultaneously for the same kref while its
count is 1, you can end up calling the 'release()' function from
kref_put() while the kref_get() increments the count back to 1 again.
To avoid that situation, you still actually need to do your own locking
of some kind when you use a kref -- even though it might try to tempt
you not to. If you don't, you'll be left with subtle races.
Which means that the 'refcounting for dummies' isn't quite as stuffed
with transparent goodness as it might seem. And it's far better to
open-code it and actually see what's going on.
Just like sleep_on(), the struct kref would appear to be a 'helper' for
naïve coders which is actually a very bad thing to use.
I'd actually advise you not to use it _ever_.
--
dwmw2