* Thomas Gleixner [off-list ref] wrote:

quoted

And if we are into getting reference counts, why not solve it at a higher 
level and get a reference count to 'x' to make sure it's safe to use? Then we 
could do:

        lock(y->lock);
retry:
        x = y->x;
        if (!trylock(x->lock)) {
                get_ref(x->count)
                unlock(y->lock);
                lock(x->lock);
                lock(y->lock);
                put_ref(x->count);
                if (y->x != x) { /* Retry if 'x' got dropped meanwhile */
                        unlock(x->lock);
                        goto retry;
                }
         }

Or so.

In the case of dcache::dentry_kill() we probably do not have to take refcounts 
and it might be actually counterproductive to do so. y->x, i.e. dentry->parent, 
cannot vanish under us, if I understand the life time rules correctly.

Ok, that's even better.

Aside of that, yes, I was thinking about a similar scheme for that. I need some 
more time to grok all the rules there :)

Ok, great! :-)

I really don't think we need a new locking primitive - and with something like the 
above we could improve the code upstream as well and make it scale better in some 
scenarios, right?

Thanks,

	Ingo