Re: [PATCH net-next v1 2/2] netpoll: avoid reference leaks

[David Miller]

From: David Decotigny <decot@xxxxxxxxxxxx>
Date: Mon, 30 Jun 2014 16:50:10 -0700

> This ensures that the ndo_netpoll_cleanup callback is called for every
> device that provides one. Otherwise there is a risk of reference leak
> with bonding for example, which depends on this callback to cleanup
> the slaves' references to netpoll info.
> 
> Tested:
>   see patch "netpoll: fix use after free"
> 
> Signed-off-by: David Decotigny <decot@xxxxxxxxxxxx>

I definitely don't understand this.

Why would we call the cleanup function of an object before it's
reference count hits zero?  It is exactly the act of reaching a
zero refcount which should trigger invoking the cleanup callback.

If a refcount is being released in another location without checking
if it hits zero and invoking the cleanup if so, _THAT_ is the bug.
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