On Tue, Aug 19, 2008 at 07:35:58AM +0000, Jarek Poplawski wrote:

quoted text
>

> > If we're removing a non-root qdisc, then we will first grab the

> > root qdisc's lock, kill the child, and release the root lock.  By

> > convention, any user of a child qdisc must have acquired the root

> > qdisc's lock because the child is only reachable through the root.

> > Therefore once we have released the root qdisc lock after killing

> > the child, we're guaranteed that no further references to that

> > child can be made.

>

> By convention, there was always this comment that destroy is under

> sch_tree_lock(), so it was legal to depend on this. I'm not afraid

> of somebody using such an under destroy qdisc - it's about a code

> inside this qdisc could refer to not destroyed part.

No no no, it's not about qdisc_destroy at all.  If you're relying

on the lock around qdisc_destroy, then you're already too late.

The qdisc should have been removed before we get to qdisc_destroy.
It's the act of removal that's protected by the root lock, and

still is.  For example, in htb_graft we do sch_tree_lock before

killing any children, this is the lock that I was referring to.
> > If for whatever reason the code does not reflect the reasoning

quoted text
> > above, please feel free to fix the code :)

>

> Sure, I'll try to look for such problems.

Of course if you find any classful qdisc that does not hold the

tree lock when killing children, then please send patches.
Thanks,

--

Visit Openswan at http://www.openswan.org/

Email: Herbert Xu ~{PmV>HI~}

Home Page: http://gondor.apana.org.au/~herbert/

PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

--

To unsubscribe from this list: send the line "unsubscribe netdev" in

the body of a message to majordomo@vger.kernel.org

More majordomo info at  http://vger.kernel.org/majordomo-info.html