Re: [PATCH] net: check negative value for signed refcnt

[Eric Dumazet]

On 01/31/2019 05:49 AM, Kirill Tkhai wrote:
> 
> 2)Not related to your patch -- it looks like we have problem in existing
> code with this netdev_refcnt_read(). It does not imply a memory ordering
> or some guarantees about reading percpu values. For example, in generic
> code struct percpu_ref switches a counter into atomic mode before it checks
> for the last reference. But there is nothing in netdev_refcnt_read().

Well, if we read an old value here, after a full and expensive synchronize_net(),
then we would have lot more problems than simply having a second round in
netdev_wait_allrefs()