Re: [patch net] net: sched: fix memleak for chain zero

Wed, Sep 06, 2017 at 07:40:02PM CEST, xiyou.wangcong@gmail.com wrote:

On Wed, Sep 6, 2017 at 4:14 AM, Jiri Pirko [off-list ref] wrote:

quoted

From: Jiri Pirko <redacted>

There's a memleak happening for chain 0. The thing is, chain 0 needs to
be always present, not created on demand. Therefore tcf_block_get upon
creation of block calls the tcf_chain_create function directly. The
chain is created with refcnt == 1, which is not correct in this case and
causes the memleak. So move the refcnt increment into tcf_chain_get
function even for the case when chain needs to be created.

Your approach could work but you just make the code even
uglier than it is now:

1. The current code is already ugly for special-casing chain 0:

       if (--chain->refcnt == 0 && !chain->filter_chain && chain->index != 0)
               tcf_chain_destroy(chain);

2. With your patch, chain 0 has a different _initial_ refcnt with others.

No. Initial refcnt is the same. ! for every action that holds the chain.
So actually, it returns it back where it should be.

3. Allowing an object (chain 0) exists with refcnt==0

So? That is for every chain that does not have goto_chain action
pointing at. Please read the code.

Compare it with my patch:

1. No special-case for chain 0, the above ugly part is removed

2. Every chain is equal and created with refcnt==1

3. Any chain with refcnt==0 is destroyed